Cooling modification

[Mxgrds]

That's my point, the air was already in there. The molecules of air and water will mix just from the circulation. Agitation speeds it up, but there are a finite number of those molecules in the contained space and it cannot create more than already exists. In other words, it may distribute the existing air more but it won't make more of it. So eventually that air will come back to the tank - as the hot/cold cycles and circulation happen. That's why the air space in the tank doesn't keep getting larger (unless you have a leak).

it depends where the air resides in the system. Once trapped in the radiator it will never finds it way back to the tank. Hence the bleed nipple on the rad. Especially not when the outlet is on the bottom. The air in the rad will push the flow to the lower part of the rad, limiting the cooling capacity. The volume the air takes in the rad needs to be compensated somewhere. Most likely the level in the tank rises until the pressure cap releases the over pressure, being air of coolant. When the air cools down, an underpressure in the tank happens. Air will be sucked in (The system is airtight when pressurised, but not for underpressure. Slowly more air and less coolant wil be in the system. This is the process how air in the rad limits the cooling capacity causing blow head gaskets. (Been there ).
Unless you switch (unknowingly) the hoses on the rad. Now the outlet is at the top, at the same place air in the rad will collect. but now it finds itself in the strong flow of the outgoing coolant. It is most likely the air will travel back with the fast flowing coolant to the thermostathouse and hopefully into the overflow to the tank. Disadvantage of switched hoses is the thermoswitch for the radfan is now on the opposite side of temperature. It will go either late or early.

 

[Mxgrds]

You want your radiator outlet hose at the lowest point on the rad and the inlet at the highest. With the outlet at the lowest point, there will always be coolant available to be sent back to the block to provide cooling (unless the system is basically empty). If you have the hoses switched and you get an air pocket at the top of the rad, you have a greater risk of drawing that air back to the block, which can cause quick temp changes as the air bubble flows (hopefully) through the block and back to the rad.

Here is the thermostat flow page from the manual you can use to check your hose set up. The Sirocco rad is different from the stock X rad, so do a thorough check to be sure of what you are looking at.
View attachment 47008

Good point. If the flow of the coolant doesn’t have enough strenght, the air will block the radiator flow. Ok. Need to change that.

 

[Dr.Jeff]

it depends where the air resides in the system. Once trapped in the radiator it will never finds it way back to the tank. Hence the bleed nipple on the rad. Especially not when the outlet is on the bottom. The air in the rad will push the flow to the lower part of the rad, limiting the cooling capacity. The volume the air takes in the rad needs to be compensated somewhere. Most likely the level in the tank rises until the pressure cap releases the over pressure, being air of coolant. When the air cools down, an underpressure in the tank happens. Air will be sucked in (The system is airtight when pressurised, but not for underpressure. Slowly more air and less coolant wil be in the system. This is the process how air in the rad limits the cooling capacity causing blow head gaskets. (Been there ).
Unless you switch (unknowingly) the hoses on the rad. Now the outlet is at the top, at the same place air in the rad will collect. but now it finds itself in the strong flow of the outgoing coolant. It is most likely the air will travel back with the fast flowing coolant to the thermostathouse and hopefully into the overflow to the tank. Disadvantage of switched hoses is the thermoswitch for the radfan is now on the opposite side of temperature. It will go either late or early.

I don't fully agree with a couple of points here. Basic physics. Although air does expand more than water as temperature rises, there is MUCH more water in the system than air (relatively no air by volume in most cases). So the overall expansion is pretty much the same as if no air existed - certainly not significantly more if a little air is trapped inside. That means the overflow tank will only allow water to exit if there is more total volume than the system will hold (at that temperature). Short of overheating (i.e. steam), the amount that expands as it heats will equal the amount that contracts when it cools. Therefore the system maintains a equilibrium...unless some other problem exists. The purpose of the overflow tank is to allow a extra volume to compensate for that ebb and flow as the system heats and cools - expands and contracts. So the total volume of cooling fluid doesn't keep getting less (if no leaks exist).

Also, the radiator (overflow tank) cap will allow excess water to exit (if the system overheats), but it should not allow air (or anything else) to enter as it cools. The seal on the cap is spring loaded to hold it closed and the negative pressure inside sucks it even tighter. So again, if no failures or abnormal problems exist, the cooling system should not allow more air to accumulate over time. If it does then a leak must exist somewhere. Under normal conditions the extra volume in the overflow tank is more than sufficient to keep the system full.

Basically there is no reason for a cooling system to accumulate more air over time (if no leaks exist). Once it is sufficiently bled (which may take considerable time, as all the tiny bubbles collect somewhere) there should be no need to do more bleeding, or to add more water (again unless it has overheated or leaks).

In other words, if the system keeps losing water or gaining air then something is wrong. A leak or overheating are the two most common causes. And the cause needs to be addressed rather than focusing on the symptoms.

 

[Dr.Jeff]

I should add a contingency statement to my last post. I concede that these cars are old and the theory of how they 'should' function doesn't always follow. Furthermore the X's cooling system design has several factors working against it, even when it is functioning well. Add engine modifications or other circumstances to it and it is even more challenged to work right. That's why we hear frequent complaints about them. But I believe in most cases a X cooling problem is due to something not being up to par. And at times it can be very difficult to find what that is.

 

[kmead]

Update. Think I solved the quick rise in temperature problem. I had a look on the hose to the Sirocco rad. One was a little bit twisted and somewhat pinched. Loosend the clam, twisted it back so the hose was perfectly round all the way. Test drove it on the highway 120 to 160 km/h. Temperature rose till just above 90 degrees. Which is good. And also not a quick rise. Amd today’s temperature was considerably higher 25 degrees then my earlier test. Happy.
one question: I noticed the hose on the rad are switched. The inlet is at the bottom, the outlet at the top. Is that a problem?

Generally it is the hottest water introduced to the radiator at the top and the cooled liquid is drawn from the bottom.

Most cars are set up this way.

 

[Bjorn Nilson]

Finally we got spring in Sweden today, almost 25 deg C. This gave me a good opportunity to test the UT engine and the new aluminum radiator in summer conditions. Cruising at 140-150 km/h is not a problem; cooling temp steady at 80 deg, oil temp close to 90 deg, intake 38 deg.
I also pushed the car really hard for some time; cooling temp climbed to 90 deg and oil temp 94 deg and stayed there which is ok. What's more worrying is that intake temp climbed to 50-55 deg. This never happened in ambient temps around 15 deg before so maybe a better pump is needed. Current charge cooler pump (cheap crap from China) has a capacity of 15l/min but maybe more flow is needed.

 

[Dr.Jeff]

maybe a better pump is needed. Current charge cooler pump (cheap crap from China) has a capacity of 15l/min but maybe more flow is needed.

That was one thing I found when I considered using a water to air intercooler. Some of the resources I read said not to use a water/air cooler for this reason. Most of the pumps out there are not very strong (in terms of pumping volume), so I wondered about their ability to offer enough thermal exchange. There are a few available with significantly more flow potential but they are quite costly. Funny enough, a typical boat bilge pump offers much more fluid flow than most of these automotive circulation pumps.

I have the same concern about using a electric pump to cool the turbo during after run. But that shouldn't require too much flow to get that job done. This might be a good use for your existing pump if you get a larger one for the cooler.

By the way, good results on the radiator.

 

[Dr.Jeff]

I should have added...the other issue I read about with a water/air cooler is the radiator for the chargecooler must be big enough and have sufficient airflow to dissipate the heat from the cooling water, otherwise it gets 'heat soak' and won't cool the 'charge' air.

 

[Mxgrds]

of the 2 UT X’s with the same setup, 1 is just fine. No overheating at all. The other one looks fine too now that I removed the twist from the radiator hose. It is slightly hotter than the other one though. I need to check the thermostat first to see if it is one with a big opening. Might be some restriction there. And need to install the oil cooler.

 

[Bjorn Nilson]

I should have added...the other issue I read about with a water/air cooler is the radiator for the chargecooler must be big enough and have sufficient airflow to dissipate the heat from the cooling water, otherwise it gets 'heat soak' and won't cool the 'charge' air.

The size of the heat exchanger is probably not the issue.

But what I've heard, the barrel type cooler that I have is not as efficient as other types. I'd rather have this type but they require much more space.

It is very strange that a difference in 5-10 deg ambient temp had such an impact on intake temp.

 

[Mxgrds]

Lots of comments, but none about my actual question. Pinching off the outlet hose from thermostat to tank, will it help for extra cooling by forcing all water to go to the radiator? What is the downside?

 

[NEG]

Try it and let us know? Theory will only get you so far....

 

[Dr.Jeff]

Lots of comments, but none about my actual question. Pinching off the outlet hose from thermostat to tank, will it help for extra cooling by forcing all water to go to the radiator? What is the downside?

See post #16.

 

[Mxgrds]

To answer my own question:
At the highest point the coolant system should be able to vent air to the tank. In the Uno system the highest point is the radiator. The X, however, has 2 highest points (excluding the heater), the top of the thermostat housing and the radiator. The hose from the housing to the tank vents that part (it should prevent air escaping to the rad), the bleed nipple vents the radiator. Or, in my case, the flooter does that automatically.
So is pinching off the hose a sensible thing to do? I don’t think so. A pocket with air in the thermostat house could be formed. Even though the strong flow will transport most air further into the system.

 

[Mxgrds]

Update. Today I reconnected the hose in the right way on the radiator. While refilling the coolant system, the outlet to the tank still pinched. I was unable to put all coolant back in. It appears the a big air pocket formed in the engine. Opening up the pinched hose let the air escape and the coolant in.
conclusion: pinching the top hose is a bad idea. An air pocket in the engine might block the total cooling and blow up the engine.

 

[Dr.Jeff]

Depending exactly which VW radiator you have, some can be flipped upside down to reposition the fan temperature sensor and/or hose connections as needed. Sometimes that allows better hose routing for non-stock applications. However others have a vent tube port at the top of one tank so they cannot be inverted. But I don't think this will help in your situation anyway.

 

[Bjorn Nilson]

Update. Today I reconnected the hose in the right way on the radiator. While refilling the coolant system, the outlet to the tank still pinched. I was unable to put all coolant back in. It appears the a big air pocket formed in the engine. Opening up the pinched hose let the air escape and the coolant in.
conclusion: pinching the top hose is a bad idea. An air pocket in the engine might block the total cooling and blow up the engine.

To mimic the UT setup, I pinched the lower hose, and it is working well. That route is always flowing regardless of temp so ev. air will escape to expansion tank.

 

[kmead]

The reason we don’t have answers on this is that the normal operation of the lines works properly for an OE engine setup, I can understand your frustration but the reality is no one has had a need to investigate this as a problem due to it not being a problem.

Another high point in the engine is the heater supply hose from the head, it is higher in the system than the thermostat. A bleeder or Prestone Flush and Fill kit could be fitted to the heater supply hose to both input coolant into the engine and bleed the system when not under pressure.

Fiat 124 owners often use this same kit in the same way, as the line to the heater on those cars is one of the high spots in that car’s system as well.

This would help with any air bubble when filling but not the one from the engine boiling coolant in the head.

It wouldn’t be a bad add in any case as it allows complete filling of the engine at coolant changeover. Just a thought.

 

[lookforjoe]

Just rev your engine and look into the tank. There is a hard flow of coolant coming from the inlet. At high rpm it is so strong it makes air bubbles which can be sucked in at the bottom.

This was an issue for me - especially with the stainless tank, as the bleed/return dumps from the very top. At least in the plastic tank it doesn't have such a waterfall effect. I made a chambered aluminum tank to minimize the aeration of the coolant being drawn back into the engine from the lower feed.

On all Volvo turbos, the turbo coolant feed comes off the return branch pipe or lower rad hose, and the turbo return enters the system below the coolant reservoir, specific location varies by model. My understanding is that this is primarily for thermo-siphon on shutdown to circulate coolant & prevent oil coking. Not sure it really does a whole lot in actual driving.

example:

 

[Mxgrds]

Thanks again for all your help. As I already stated, pinching the hose is not a good idea, it is even a bad idea. The Fiat engineers new that air will be drown into the engine (small gass bubbles) and designed the thermostathousing at the top of coolant circulation on the engine, so the air will leave the engine there. On the Uno the air will travel to the rad which lies a bit above the engine. From the rad it travels to the, even heigher, tank to split the air from the coolant. In the X layout there is no rad close by and it lies lower than the engine. So they shortcutted the airflow from the thermostathouse directly to the higher tank. Unfortunately, at high revs and a strong flow, some air will get trapped in the hot coolant and will travel in the direction of the radiator. Once in the radiator the flow slows done and cools off, leaving that air in the radiator. Bleeding the rad (periodically) is key to prevent overheating. Leaver guys at Fiat, but they could have done a better job at the radiator side.