Measuring flow rate on a water pump

[Roxyred]

Heya, I have an 85 Bertone that’s stock everything. It has had intermittent cooling issues, usually on hot days and in traffic. I redid the radiator and added an additional stock cooling fan (aka dual fans like the ac model x’s) and that helped, but still getting way warmer than I’d like on short trips. It occasionally has a brief drop in temp, but creeps back up despite the fans going full force.

Having read some of the other posts here, I’m debating if I need a thermostat or a new pump, and where to start.

specs on mine
1500
no ac
stock original radiator (though recently refreshed and new hoses throughout)
new thermo fan switch

Questions:
how can I check the flow rate of the pump while it’s on the car? What do I need?
should I just go ahead and swap the thermostat since that’s fairly easy and cheap?
what other things do you all suggest for rooting out the cause before just swapping things out?

bonus info: my red 86 has none of these issues, and stays in perfect temp range all the time. Also fully stock, but with ac (though the ac is not connected)

Thanks for your input!

 

[Dan Sarandrea (Phila)]

What temps does it show on the temp gauge when you consider it to be behaving normally, and what does it show when these intermittent cooling issues show up? What temp is "way warmer than I like"?

Describe how the stock rad was "refreshed."

"It occasionally has a brief drop in temp" can be an indicator of air pockets, has there been anything done to bleed/burp the system?

It would be remarkably rare for this to turn out to be a coolant flow problem caused by something wrong within the pump---something extraordinary like the impeller decomposing from rust, or the impeller somehow slipping on its shaft.

A pump-related issue could develop if the pump itself were replaced and random production tolerances added up not in your favor to create too much of a gap between the impeller and the pump body. There is a reasonable expectation that excessive tolerances could result in inadequate cooling, but AFAIK no one has ever posted here with anything you could call a controlled experiment.

 

[Dr.Jeff]

Honestly trying to accurately measure the pump's flow would be difficult to do. And there are no standards to compare the results with so it really won't tell you anything.

I agree with Dan, what do you mean by "refreshed" radiator? There is a good chance the core has a lot of crud built up inside that won't get removed with standard flushing. It will need to go to a radiator shop to be "rodded out" or at least dip tank cleaned and high pressure flushed.

I would replace the thermostat regardless. They do get stuck or weak. And it is cheap and easy to do. You might even consider using a step cooler one.

I'm not sure if I correctly understood Dan's comment about water pump failures. In my experience there is a high likelihood of the impeller rusting away, the housing corroding and pitting away, the bearing becoming stubborn or loose - all affecting the impeller clearance as well as other efficiency issues. So this is another item I'd replace. Water pumps are a service item in my opinion.

You may also have blockage in the long narrow cooling pipes that travel the length of the car in the lower tunnel. I've even seen several that were crushed from road damage, significantly restricting the internal flow.

As Dan said, trapped air in the system can cause intermittent hot/cold periods. Due to it's design it can be difficult to completely bleed the system effectively.

And don't count on the stock dash temp gauge being accurate. They are not. You might not have any problems other than gauge errors. Therefore double check the temps with a non-contact thermo gun.

There's even more possibile failure areas on these cooling systems. But those are the most likely in my opinion.

 

[dllubin]

Heya, I have an 85 Bertone that’s stock everything. It has had intermittent cooling issues, usually on hot days and in traffic. I redid the radiator and added an additional stock cooling fan (aka dual fans like the ac model x’s) and that helped, but still getting way warmer than I’d like on short trips. It occasionally has a brief drop in temp, but creeps back up despite the fans going full force.

Having read some of the other posts here, I’m debating if I need a thermostat or a new pump, and where to start.

specs on mine
1500
no ac
stock original radiator (though recently refreshed and new hoses throughout)
new thermo fan switch

Questions:
how can I check the flow rate of the pump while it’s on the car? What do I need?
should I just go ahead and swap the thermostat since that’s fairly easy and cheap?
what other things do you all suggest for rooting out the cause before just swapping things out?

bonus info: my red 86 has none of these issues, and stays in perfect temp range all the time. Also fully stock, but with ac (though the ac is not connected)

Thanks for your input!

Have you checked the impeller to housing clearance? It should be between 0.8mm and 1.3mm or it will not operate efficiently. If the pump was replaced without checking, it could be contributing to the problem.

 

[Roxyred]

Ok, let’s see if I can answer these in the correct order:

I am basing “normal” as how my 86 behaves with no issues. It typically sits right at halfway on the gauge, and varies a bit up but cools down quickly when the fans come on. Never gets above 3/4 of the way to red on the gauge. I’d have to go out and look at the gauge to give you exact numbers.

the 85 that is overheating creeps up to 3/4 of the way, and never cools off despite fans. often it creeps higher, today it didn’t touch the red but came awfully close. Based on the gauge reading during warm up time, driving, etc, I don’t think it’s the gauge. I need to find my temp gun, it got lost in a move.

It’s possible it is a bubble, I did the typical bleed by cracking the petcock on the radiator and running it through the paces. If you have some additional tricks for burping to ensure the air is all out, please share! I haven’t figured out how to do the “really tall funnel” trick to get the fluid level higher than the motor, as I do on my spider.

the radiator went to an old school radiator shop and was completely rodded out and resealed, not just drained or sorta cleaned. That did help some but hasn’t fixed the problem.

I suppose it’s possible I have a blockage in the lower under chassis rails, however the car is in excellent condition, and I am the second owner so I hadn’t had the abuse of hitting something to squish those (my 86 has had the rails replaced).

Since I am the second owner, it may be the original water pump in the car. I don’t have access to the original owner’s files at this time (long story) but that’s part of why I think I may need a new pump. I’ll do the thermostat because eh, why not.

I’ll give it another go with the burping, but have not had much luck with that helping so far.

 

[Roxyred]

Have you checked the impeller to housing clearance? It should be between 0.8mm and 1.3mm or it will not operate efficiently. If the pump was replaced without checking, it could be contributing to the problem.

No, the pump is still on the car.

 

[Dan Sarandrea (Phila)]

Ok, let’s see if I can answer these in the correct order:

I am basing “normal” as how my 86 behaves with no issues. It typically sits right at halfway on the gauge, and varies a bit up but cools down quickly when the fans come on. Never gets above 3/4 of the way to red on the gauge. I’d have to go out and look at the gauge to give you exact numbers.

the 85 that is overheating creeps up to 3/4 of the way, and never cools off despite fans. often it creeps higher, today it didn’t touch the red but came awfully close. Based on the gauge reading during warm up time, driving, etc, I don’t think it’s the gauge. I need to find my temp gun, it got lost in a move.

It’s possible it is a bubble, I did the typical bleed by cracking the petcock on the radiator and running it through the paces. If you have some additional tricks for burping to ensure the air is all out, please share! I haven’t figured out how to do the “really tall funnel” trick to get the fluid level higher than the motor, as I do on my spider.

the radiator went to an old school radiator shop and was completely rodded out and resealed, not just drained or sorta cleaned. That did help some but hasn’t fixed the problem.

I suppose it’s possible I have a blockage in the lower under chassis rails, however the car is in excellent condition, and I am the second owner so I hadn’t had the abuse of hitting something to squish those (my 86 has had the rails replaced).

Since I am the second owner, it may be the original water pump in the car. I don’t have access to the original owner’s files at this time (long story) but that’s part of why I think I may need a new pump. I’ll do the thermostat because eh, why not.

I’ll give it another go with the burping, but have not had much luck with that helping so far.

The center point on the gauge is 190. Each small hashmark is worth 5 degrees.

More questions: what coolant and what mix? What is the pressure value on your coolant tank cap? Any signs of leakage in the system? (Sometimes you can smell a leak before you find the leak.)

What is the condition of and tension on the WP-ALT-CRANK belt?

If you were to simply start the car and let it idle (for time's sake let's say you do this experiment with the engine cooler than operating temp [190] but not first thing in the morning cold---let's say within a range of 140-170 on the gauge), and with absolutely no intervention on your part whatsoever, at what temp gauge value would the fan(s) come on?

 

[kmead]

It could be that your gauge or the sender to the gauge is not accurate or is more sensitive than the one in the red one (funny I have the same two color combo X’s in my garage, hmmm).

My brown and gold car has always read low on the gauge and only gets up to 190 or above if I have just come off the highway or autox course. For the last two years I have not had a fan connected to the electrical system because I drive it on an open road with no traffic and the switch in the radiator had failed.

During my current cooling system redo I am flushing the system using a chemical, replacing all hoses, the gauge sender, the fan switch with a two temp unit, the oh so frozen heater valve and the thermostat. As I am doing it as a wholesale set, I won’t know when I am done what had the most effect if I now run at 190 all the time or if the car keeps at its 165-170 degrees.

You might uses a laser temperature gun to get actual temps of the various components to see what is really happening compared to your 37 year old gauge and sender…

 

[RichG]

Ok, let’s see if I can answer these in the correct order:

I am basing “normal” as how my 86 behaves with no issues. It typically sits right at halfway on the gauge, and varies a bit up but cools down quickly when the fans come on. Never gets above 3/4 of the way to red on the gauge. I’d have to go out and look at the gauge to give you exact numbers.

the 85 that is overheating creeps up to 3/4 of the way, and never cools off despite fans. often it creeps higher, today it didn’t touch the red but came awfully close. Based on the gauge reading during warm up time, driving, etc, I don’t think it’s the gauge. I need to find my temp gun, it got lost in a move.

It’s possible it is a bubble, I did the typical bleed by cracking the petcock on the radiator and running it through the paces. If you have some additional tricks for burping to ensure the air is all out, please share! I haven’t figured out how to do the “really tall funnel” trick to get the fluid level higher than the motor, as I do on my spider.

the radiator went to an old school radiator shop and was completely rodded out and resealed, not just drained or sorta cleaned. That did help some but hasn’t fixed the problem.

I suppose it’s possible I have a blockage in the lower under chassis rails, however the car is in excellent condition, and I am the second owner so I hadn’t had the abuse of hitting something to squish those (my 86 has had the rails replaced).

Since I am the second owner, it may be the original water pump in the car. I don’t have access to the original owner’s files at this time (long story) but that’s part of why I think I may need a new pump. I’ll do the thermostat because eh, why not.

I’ll give it another go with the burping, but have not had much luck with that helping so far.

having taken apart an X19 engine recently i found a huge amount of limescale in the water pump housing blocking flow so thats a good place to go next after the radiator.

 

[Roxyred]

The center point on the gauge is 190. Each small hashmark is worth 5 degrees.

More questions: what coolant and what mix? What is the pressure value on your coolant tank cap? Any signs of leakage in the system? (Sometimes you can smell a leak before you find the leak.)

What is the condition of and tension on the WP-ALT-CRANK belt?

If you were to simply start the car and let it idle (for time's sake let's say you do this experiment with the engine cooler than operating temp [190] but not first thing in the morning cold---let's say within a range of 140-170 on the gauge), and with absolutely no intervention on your part whatsoever, at what temp gauge value would the fan(s) come on?

Hi Dan,

coolant is just the standard Preston’s green stuff, mixed 1/2 and 1/2. I would need to check the pressure value, I ran a dye trace last year and had the slightest leak (could smell it but not see it) coming from the thermostat housing. That seems to have been resolved.

Belt is good, as I just tensioned it due to a slight squeal on launch. Condition looks nice.

My fans on this x come on later than the red one, and I wanna say that they come on at the 3/4 mark or just a hair over. I actually initially thought my fans weren't coming on, as I did an idle in the driveway test previously and the temp slowly just climbed and climbed without them kicking on. but driving it yesterday they were working perfectly and were on at the 3/4 mark.

This has me thinking…based on what I’ve read here (thanks forum folks!) the fan sensor is at the backside of the radiator flow, correct? Therefore if the flow isn’t great, and the motor side is hot, it might take a lot longer for the fans to engage while idle vs. being pushed well by the pump at speed, if the pump is weak to start. Thoughts?

 

[Roxyred]

having taken apart an X19 engine recently i found a huge amount of limescale in the water pump housing blocking flow so thats a good place to go next after the radiator.

Yeah, since I am still waiting for access to the original records, I am not sure how old the pump is, which has me headed that way. It’s a pretty straight forward system, so kinda feeling like a process of elimination.

 

[RichG]

Yeah, since I am still waiting for access to the original records, I am not sure how old the pump is, which has me headed that way. It’s a pretty straight forward system, so kinda feeling like a process of elimination.

the pump maybe fine it was the housing next to it which was blocked up but the pump is cheap to buy so its not worth not changing as you work your way round the system. i think sometimes we forget how old these cars and parts in them are for instance see attached an image of the engine water jacket with the cover removed where the yellow crystals are was full of rust etc which i dug out and washed out

 

[Roxyred]

If I wanted to get a cooler functioning thermostat, what range should I look for from stock? So it opens sooner?

 

[kmead]

If I wanted to get a cooler functioning thermostat, what range should I look for from stock? So it opens sooner?

I wouldn’t suggest a cooler engine thermostat, this won’t reduce your engine temperature if the system isn’t working properly. It just has the engine running cooler than it should and it won’t hold the peak temperature down. As your current thermostat isn’t keeping the temperature under control, how will a thermostat which opens earlier do any better?

The thermostat could be not opening properly and cycling hot coolant around the engine rather than opening fully to allow the cooled coolant to go through. Replacing the thermostat would take care of this if indeed it is the problem

I would be looking at the water pump, the general condition of the piping and radiator as the culprits. Replacing the thermostat would go along with any refurbishment of the cooling system (I am replacing mine with the ‘premium’ thermostat MWB sells as I suspect mine isn’t working properly, likely stuck all the way open).

If you want to have the fan come on sooner MWB does sell a lower temperature thermo switch for the radiator.

You could add the second fan and have that triggered either at the same time or at a higher temperature. There is a VW thermoswitch which can control two fans to go on and off at two different temperatures.
Low Temperature Fan Switch - 2-speed - VW Mk1 w/ AC, Mk2, '89-93 Corrado - 85C / 93C
https://www.fcpeuro.com/products/audi-vw-engine-cooling-fan-switch-251959481k-1#fitment
Audi VW Engine Cooling Fan Switch (Vanagon EuroVan A8 S8) - Meyle 251959481K
https://store.ngpracing.com/low-tem...ed-vw-mk1-w-ac-mk2-89-93-corrado-85c-93c.html

You can use the existing relay opening for the second fan which is already wired in the fuse box assembly for the AC system. The wires for the second fan are already behind the radiator. The temperature sensor wires are also there and would need to be extended to the thermoswitch. If tripping both at the same time you could extend the existing ground for the current fan relay to the second fan relay’s ground pin.

 

[Roxyred]

I wouldn’t suggest a cooler engine thermostat, this won’t reduce your engine temperature if the system isn’t working properly. It just has the engine running cooler than it should and it won’t hold the peak temperature down. As your current thermostat isn’t keeping the temperature under control, how will a thermostat which opens earlier do any better?

The thermostat could be not opening properly and cycling hot coolant around the engine rather than opening fully to allow the cooled coolant to go through. Replacing the thermostat would take care of this if indeed it is the problem

I would be looking at the water pump, the general condition of the piping and radiator as the culprits. Replacing the thermostat would go along with any refurbishment of the cooling system (I am replacing mine with the ‘premium’ thermostat MWB sells as I suspect mine isn’t working properly, likely stuck all the way open).

If you want to have the fan come on sooner MWB does sell a lower temperature thermo switch for the radiator.

You could add the second fan and have that triggered either at the same time or at a higher temperature. There is a VW thermoswitch which has can control two fans. https://store.ngpracing.com/low-tem...ed-vw-mk1-w-ac-mk2-89-93-corrado-85c-93c.html

You can use the existing relay opening for the second fan which is already wired in the fuse box assembly for the AC system. The wires for the second fan are already behind the radiator. The temperature sensor wires are also there and would need to be extended to the thermoswitch. If tripping both at the same time you could extend the existing ground for the current fan relay to the second fan relay’s ground pin.

wow! Thanks Karl! That’s a thorough assessment, and I’ll check for the lower temp switch on MWB, since I’ll already have to drain part of the system for the other issues.

 

[Dr.Jeff]

I wouldn’t suggest a cooler engine thermostat, this won’t reduce your engine temperature if the system isn’t working properly. It just has the engine running cooler than it should and it won’t hold the peak temperature down. As your current thermostat isn’t keeping the temperature under control, how will a thermostat which opens earlier do any better?

The thermostat could be not opening properly and cycling hot coolant around the engine rather than opening fully to allow the cooled coolant to go through. Replacing the thermostat would take care of this if indeed it is the problem

I would be looking at the water pump, the general condition of the piping and radiator as the culprits. Replacing the thermostat would go along with any refurbishment of the cooling system (I am replacing mine with the ‘premium’ thermostat MWB sells as I suspect mine isn’t working properly, likely stuck all the way open).

If you want to have the fan come on sooner MWB does sell a lower temperature thermo switch for the radiator.

You could add the second fan and have that triggered either at the same time or at a higher temperature. There is a VW thermoswitch which can control two fans to go on and off at two different temperatures.
Low Temperature Fan Switch - 2-speed - VW Mk1 w/ AC, Mk2, '89-93 Corrado - 85C / 93C
https://www.fcpeuro.com/products/audi-vw-engine-cooling-fan-switch-251959481k-1#fitment
Audi VW Engine Cooling Fan Switch (Vanagon EuroVan A8 S8) - Meyle 251959481K
https://store.ngpracing.com/low-tem...ed-vw-mk1-w-ac-mk2-89-93-corrado-85c-93c.html

You can use the existing relay opening for the second fan which is already wired in the fuse box assembly for the AC system. The wires for the second fan are already behind the radiator. The temperature sensor wires are also there and would need to be extended to the thermoswitch. If tripping both at the same time you could extend the existing ground for the current fan relay to the second fan relay’s ground pin.

Unless of course the thermostat IS the reason for the high running temp. Which is what I was saying may be one possibility. In which case there is the option to go a step cooler for the replacement stat. However as you say, that's assuming the rest of the cooling system is working properly.

Going with a little cooler thermostat is not "running cooler than it should". Most manufacturers provided different temps of stats depending on the emissions requirements, the climate where the vehicle was being sold, the accessories included (e.g. AC), the particular engine spec, etc. There is a reason a selection of thermostat temperatures exists. So each case needs to be evaluated for its own merits. Although most of this is more typical for other car manufacturers, it's my understanding Fiat used more than one temp of stat in the X at different times over the course of it production??

 

[Jonohhh]

Does the heater function also basically cease at idle? That's how my 85' was - likely caused by incorrect water pump clearance as the impeller was firmly on the shaft and completely intact.

I'd have to keep it around 3000 rpm at stop lights in the winter to maintain heat inside the car, and during the warmer months it'd overheat at idle.

 

[kmead]

Unless of course the thermostat IS the reason for the high running temp. Which is what I was saying may be one possibility. In which case there is the option to go a step cooler for the replacement stat. However as you say, that's assuming the rest of the cooling system is working properly.

Going with a little cooler thermostat is not "running cooler than it should". Most manufacturers provided different temps of stats depending on the emissions requirements, the climate where the vehicle was being sold, the accessories included (e.g. AC), the particular engine spec, etc. There is a reason a selection of thermostat temperatures exists. So each case needs to be evaluated for its own merits. Although most of this is more typical for other car manufacturers, it's my understanding Fiat used more than one temp of stat in the X at different times over the course of it production??

Once the thermostat is open it can’t make the engine run any cooler than the open position.

If the thermostat is defective and allowing continuing recirculation of the hot coolant, as these are two stage thermostats, replacing it with one that works to keep the engine at whatever temperature desired would work. If the radiator is plugged and not properly shedding the heat then no amount of regulation by the thermostat will keep the engine cool.

There are lower temp thermostats available, I don’t know if they installed a lower temp thermostat in earlier Xs though my 75 operated at similar indicated temps as my 87 does.

A thermostat functions by opening and closing based on the temperature of the engine side of the coolant outflow, as it opens more directing hot coolant to the radiator it allows more cooled coolant to the engine from the radiator. It will constantly fluctuate with some hysteresis due to the time for the wax to actuate it which is part of why we see variation. At a certain point it is fully open and the engine is only receiving cooled coolant, if that coolant is not cold enough to bring the temperature down in the engine we see the gauge rise. If the radiator or the pump are not working properly you either are not getting cold enough coolant on the return leg or the pump is not pumping enough volume of cooled coolant to pull the engine temperature down.

It is why all three major elements have to be in good condition and working properly. There are other externalities such as sediment in the block, pipe blockage, air in the system, bad thermoswitch for the fans (mine has been dead for two years) and so on which can also be causal reasons for high temps in the engine. Fixing the three leading controllers of temperature is the best way to resolve the problem and if it persists then more rigorous measures would need to be pursued.

Actually going to a cooler thermostat is in fact running cooler than it should, if the system is designed for a specific set temperature for combustion, emissions and heat transfer. Very few manufacturers will give you a different thermostat for a given engine as developed. Do they have other thermostats or have others made other thermostats, yes. But if you went to the Fiat dealer (or Ford, Honda Toyota etc) and asked for a new thermostat they will give you one, not a choice.

 

[Dr.Jeff]

Once the thermostat is open it can’t make the engine run any cooler than the open position.

If the thermostat is defective and allowing continuing recirculation of the hot coolant, as these are two stage thermostats, replacing it with one that works to keep the engine at whatever temperature desired would work. If the radiator is plugged and not properly shedding the heat then no amount of regulation by the thermostat will keep the engine cool.

There are lower temp thermostats available, I don’t know if they installed a lower temp thermostat in earlier Xs though my 75 operated at similar indicated temps as my 87 does.

A thermostat functions by opening and closing based on the temperature of the engine side of the coolant outflow, as it opens more directing hot coolant to the radiator it allows more cooled coolant to the engine from the radiator. It will constantly fluctuate with some hysteresis due to the time for the wax to actuate it which is part of why we see variation. At a certain point it is fully open and the engine is only receiving cooled coolant, if that coolant is not cold enough to bring the temperature down in the engine we see the gauge rise. If the radiator or the pump are not working properly you either are not getting cold enough coolant on the return leg or the pump is not pumping enough volume of cooled coolant to pull the engine temperature down.

It is why all three major elements have to be in good condition and working properly. There are other externalities such as sediment in the block, pipe blockage, air in the system, bad thermoswitch for the fans (mine has been dead for two years) and so on which can also be causal reasons for high temps in the engine. Fixing the three leading controllers of temperature is the best way to resolve the problem and if it persists then more rigorous measures would need to be pursued.

Actually going to a cooler thermostat is in fact running cooler than it should, if the system is designed for a specific set temperature for combustion, emissions and heat transfer. Very few manufacturers will give you a different thermostat for a given engine as developed. Do they have other thermostats or have others made other thermostats, yes. But if you went to the Fiat dealer (or Ford, Honda Toyota etc) and asked for a new thermostat they will give you one, not a choice.

I find it is more common for a failed thermostat to get stuck closed rather than open. And that is what I was referring to.

 

[Dr.Jeff]

Actually going to a cooler thermostat is in fact running cooler than it should, if the system is designed for a specific set temperature for combustion, emissions and heat transfer. Very few manufacturers will give you a different thermostat for a given engine as developed. Do they have other thermostats or have others made other thermostats, yes. But if you went to the Fiat dealer (or Ford, Honda Toyota etc) and asked for a new thermostat they will give you one, not a choice.

That hasn't been my experience. Perhaps it depends on the vehicles in question.