Interesting Temperature Question

H

halojm

True Classic
I drove my X all the way from Pennsylvania down to North Carolina for FFO and it drove flawlessly, averaging 35mpg at 75mph. Ran consistently 190 degrees except when I would let off the gas quickly it would run 225 degrees for 5 to 8 seconds then drop quickly back to 190 degrees. I pounded the car hard during some of the events at FFo and it never overheated. It has a newly rebuilt high compression engine correctly timed, completely cleaned out cooling system, recored extra efficiency radiator, new thermostat. Per Matt's recommendation, I bled the cooling system but it still did it on the return trip. Any ideas?
Dave
 
Heat Soak.

Sounds like the car is working fine along with the cooling system. If you are running the car as you said then back off the gas think for a moment. The engine is loaded producing heat, the water pump is circulating the coolant the rad is disapating the heat, then you back of the gas, drop the RPM, the mass of the engine still has a lot of heat from the hard run. ( Heat Soak ) the water temperature rises and that slug of hot water now reaches the rad and cools, the differential is higher 225 degree water hitting the 85 degree air flow at the rad. That water cools and returns to the engine dropping the temperature. This is no different than when you come off of the highway ramp. High load then no load and no wind from 70 MPH air flow on to the rad. Heat Soak now rises the engine coolant temperature.

Sounds like everything is working fine.

TonyK.

Grimsby Ontario Canada.
 
TonyK said:
Sounds like the car is working fine along with the cooling system. If you are running the car as you said then back off the gas think for a moment. The engine is loaded producing heat, the water pump is circulating the coolant the rad is dissipating the heat, then you back of the gas, drop the RPM, the mass of the engine still has a lot of heat from the hard run. ( Heat Soak ) the water temperature rises and that slug of hot water now reaches the rad and cools, the differential is higher 225 degree water hitting the 85 degree air flow at the rad. That water cools and returns to the engine dropping the temperature. This is no different than when you come off of the highway ramp. High load then no load and no wind from 70 MPH air flow on to the rad. Heat Soak now rises the engine coolant temperature.
Sounds like everything is working fine. TonyK.
Click to expand...

This is the exact reason I installed an axillary pump.
The engine doesn't circulate adequately at low RPM.
Simply, the stock pump is too small.

Read my solution HERE:
 
I suspect something else is going on.

And we have not stumbled upon it yet.But we should all keep looking.

I just drove my X all over Albuquerque for two days in the hottest weather of the summer. High 90sF. Many stop lights. Lots of road work with the usual multiiple light changes before making it through. Screaming high heat everywhere. The eyes could only see things in bleached white heat. But the X sat at 190 whether moving or sitting. The fan kick in when the gauge went to a hair over 190 and out when it was back at 190 and it appeared happy. In fact, it seemed to have a bit more pep than usual. So I flogged it. You have to understand that this radiator has never been cleaned out, nor the engine rebuilt. Everything is stock, more or less. So why do some Xs do fine when other seem to overheat at the first chance? Another mystery.
 
I agree and have tested this.

90+ degree weather and doing 80mph down a moutain pass.

in gear, temps were *195. I figured i'd take it out of gear and coast and at 80 the wind would still be cooling fine.

Temps started to rise. revved up to 2500rpm in neutral and temps
dropped back down.

Solution would be to change the water pump pulley size to get it up to proper speeds at idle. But i'd suspect they had designed it as an underdrive pulley at the factory to gain some hp.
 
Did it overheat?

If not, then conventional wisdom is it's fine.

On my recent trip with my daughter to Oregon'10 my car ran about 1/2 the gauge most of the way. When we reached the Rogue Vally in southern Oregon, temps began to climb. This was in part due to having the top on and the A/C on to prevent our skulls from sizzling.

Running up the 40 mile hill to Howard Prairie Lake Resort the temps rose to 3/4 gauge. Still didn't overheat. When we plateaued, the cooler mountain temps and lighter engine load let the engine cool back to just above 1/2 gauge.

Later testing with my IR thermometer showed the gauge was pretty accurate. It was just hot there, mid 90's in the mountain shade. Temps at the track day event (pics and vids to come) were in the triple digits, and still no overheating. Just ran hot as would be expected.

A hot engine trying to cool with hot air will run hot, but as long as the cap is good, the system is bled of air bubbles, it will be fine.

I expect that differences between X's is largely due to ambient temps, followed by cooling system condition followed by electrical differences. I've seen temp gauges off by considerable amounts due to corrosion and loose sender tolerances. As long as you know what your system does and what to expect of it, you should be fine.

I really do thing everyone should get an IR thermometer (like say HF, where mine is from), so they can get accurate and safe measurements and know whether or not the indicated temp is the actual temp. :bla:
 
Mods

The difference in car cooling capacity is Modifications. Cam changes, timing changes, compression changes, fuel delivery changes. All of these produce more heat than the cooling system at times can handle. I run dual rads on my car and do not have cooling problems.

TonyK.

Grimsby Ontario Canada.
 
I wonder if something else as at play-- like an electrical issue. I'm not aware of any automotive temp sending units and analog gauges that respond that quickly. If the gauge is indeed indicating a 35 degree variation in under 10 seconds I can't imagine it could be anything other than electrical.

///Mike
 
Gauge response time

///Mike said:
I wonder if something else as at play-- like an electrical issue. I'm not aware of any automotive temp sending units and analog gauges that respond that quickly. If the gauge is indeed indicating a 35 degree variation in under 10 seconds I can't imagine it could be anything other than electrical. ///Mike
Click to expand...

I can't speak for the response time of the sensor, as that has to heat up with the block/fluid it senses,
but the gauge itself responds rather fast. Electrically, if you shut down your car (when hot) and power
it back up again, the needle settles within about a second. Same for oil, (if you have one!) and fuel.

Accuracy? That's another story completely... :shock:
 
Last edited:
Agree with LarryC on this...

We've had an unusual stretch of pretty warm weather here in the Northeast this summer and I've been driving my X in it. My temp gauge hits 190 and just stays there... whether I'm hot-footing it or just puttin' around. The only difference I notice is how often the fans cycle.

The two previous X's I've had acted the same.. the only time one didn't was when I had a water pump problem. All cars were/are essentially stock.

The thing that would concern me was how fast your temp gauge is changing. I don't think 190 to 225 in 8 seconds could be "hot soak". If those temps are real and its not some electrical issue, temp changes that fast suggest something else... still some air in the system maybe?...
 
Dave... as TK and Larry C said...

You are amongst the CHARMED ones on this site...

One thing you did not mention is whether or not you have A/C or an A/C condensor in the way also... I think this may be the ONE big difference in cooling... and its the ONLY thing I can think of when it comes to Bob Brown's issue... as he has gone thorugh virtually everything on that car before he installed the auxilliary pump.

Secondly... I experience the same spike in temps when I exit a freeway and come to a stop after cruising at 75 and 103 temps outside. Temp will rise and fans (TWO STOCKERS) will come on and control the issue, cycle and stop.

One FLAW I useta have is when I reinstalled the radiator and failed to place it CENTERED in its top mount. It will fit up there in FRONT or in the REAR if the mount... and the air flow will be ADVERSELY affected. It NEEDS to be in there correctly... you can tell by FEELING for the purge valve and insuring it is centered in its hole.

Purging all the air from the system... I use a flush T in the heater hose and backfill out the reservoir... and I also fill the reservoir to about 3/4 full for just a skosh more capacity.

Otherwise... I don't know what else to suggest... I don't wanna get into removing RAIN TRAYS here... but all these things I believe contribute to a cooler and more stable running temperature.

Basically... you are operating in a NORMAL capacity... that probably could be a bit better.
 
High Voltage.

I've had a Bosch volt regulator go bad. It let the voltage go way too high, then drop back down to normal. This, of course, made the guages all read high, and made the lights really bright.

Engine RPM made it go crazy. Blipping the headlights would make it work again....for a while. I replaced it before any more drive time.
 
I had this happen to me once also...

... before I had any relay mods and BWMs... and WOW... was it cool for a minute or two. I believe I read 18 volts!

I too shut it down and had the entire alternator rebuilt at the time for about 40 bucks! Really coulda fried the Ignition module and shorten the life of the radio and lights!

HA!
 
bbrown said:
I can't speak for the response time of the sensor, as that has to heat up with the block/fluid it senses,
but the gauge itself responds rather fast. Electrically, if you shut down your car (when hot) and power
it back up again, the needle settles within about a second. Same for oil, (if you have one!) and fuel.
Click to expand...

Point well taken Bob. In actual operation the gauge operation seems well damped, but that apparently comes from the sender.

I'd still be looking at possible electrical causes-- bad regulator, brushes, or ground. Assuming the indicated temp varied that much that quickly, of course...

///Mike
 
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