After running on the highway at about 75+ mph for extended periods, my 91 Q’s water temp starts rising. The first time it did this, ambient temp was 70 or so only. In the four years I’ve owned it, the temp has always been rock steady at the 3 o’clock position until this year. Sitting in hot traffic doesn’t seem to be as much of a problem strangely enough.
My first unsuccessful attempt at curing this involved replacing both caps (filler and radiator). Two months prior to my problem starting, I replaced the thermostat (with OEM) as part of regular maintenance and had the system flushed. I read over other posts on this subject and found that sometimes the thermostat can get stuck after a flushing. I replaced it again to no avail. I then removed the radiator and cleaned it as best I could inside and out, and replaced the foam surrounds. I thought that this for sure would cure it given the amount of dirt I cleaned out. Also installed B&M transmission cooler bypassing in-radiator unit. Still, she runs hot.
Does anyone have some advice for me? My only last guess is the fan clutch, which doesn’t seem to be obviously broken. Is there some way to test it for proper function?
I do not think the temp gauge is erratic, and I also have a hard time believing I need a new radiator given that temps were rock steady last year – (how could the performance deteriorate so fast?)
Thanks in advance,
The Fly
Help - hot running Q
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Q451990
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I think it may be time for a new radiator. The dash gauge is very flat at 3 o'clock, so you may have been slightly overheating last year too, but it just now got to the point that you can tell with the dash gauge. As far as the fan clutch, I'm not sure how to test it... it should be harder to turn the fan when the engine is hot than cold, but other than that, I really haven't had a problem...
Being in T3's home town, I'd sure take advantage of their expertise on this!
Heath
Being in T3's home town, I'd sure take advantage of their expertise on this!
Heath
You don't the thermostat in backwards do you? I know stupid question, but it's possible.
My guess first off is the radiator is just worn out. Sediment in tap water coats the internal sufaces inside and causes two problems. First these deposits form an insulating barrier between the water and the metal tubing. Second sediment will constrict the core and reduce maximum flow.
This can be prevented/slowed (but not curred) by using distilled water.
Check the electric aux fan located up front - is it running? This fan is activated by very hot water in the LH side of the rad (or by high pressure in the AC system) Check the fuse on this fan. Try shorting the connector with some thick wire and ensure the fan runs.
Also check the water temp (just after running) on the rad outlet (lower LH) is it very very hot or around 100 degrees? If the rad outlet temp is very high, it's time to think about getting a new rad.
The fan is unlikely, though not impossible. At 70 degrees, the fan shouldn't need to engage the clutch much. Pop the hood and shut the engine off, how long does the fan keep spinning? It should stop pretty much right away. Much run on show it's too loose.
My guess first off is the radiator is just worn out. Sediment in tap water coats the internal sufaces inside and causes two problems. First these deposits form an insulating barrier between the water and the metal tubing. Second sediment will constrict the core and reduce maximum flow.
This can be prevented/slowed (but not curred) by using distilled water.
Check the electric aux fan located up front - is it running? This fan is activated by very hot water in the LH side of the rad (or by high pressure in the AC system) Check the fuse on this fan. Try shorting the connector with some thick wire and ensure the fan runs.
Also check the water temp (just after running) on the rad outlet (lower LH) is it very very hot or around 100 degrees? If the rad outlet temp is very high, it's time to think about getting a new rad.
The fan is unlikely, though not impossible. At 70 degrees, the fan shouldn't need to engage the clutch much. Pop the hood and shut the engine off, how long does the fan keep spinning? It should stop pretty much right away. Much run on show it's too loose.
Thanks guys. The stat is in correctly (spring side towards engine) according to service manual. My radiator has been flushed 2x in the past months and is much cleaner on the outside now compared with when it was running cool all the time 6000 miles ago last summer - a real puzzler. I guess I'll take her back to T3 for a diagnosis.
So the higher speed cooling is not really affected by the main fan?
Thanks,
So the higher speed cooling is not really affected by the main fan?
Thanks,
Correct.
It is almost certainly your rad (unless there is a blockage in the air flow somewhere)
At high vehicle speed, lots of air blows through the rad.
The question about the electric fan was more to help determine if the RAD was bad. In moderately warm weather with the AC off it shouldn't come on above 40 MPH.
The cooling capacity of the rad is a function of heat injected vs. the mass and temp of air flowing across it. At highway speeds the air wins due the huge mass per second flowing across it and the thermostat shouldn't need to open all the way. Stopped in traffic in gear, with the AC on, the heat from the coolant will win and the temp will eventually start to rise in every car.
If youre rad is coated inside with limestone/calcium, there is little a flush will do for it, especially if you or the shop is using tap water. The trouble is calcium just doesn't dissolve that easily.
The outside of the rad is important too, as you note, so is the performance of the AC rad - if it's plugged with leaves and reduces airflow that cuts cooling capacity.
Since a new rad for you car will cost $370, you might try a few of the tricks first - flush it with distilled water and cleaner. Run it with just 10% antifreeze and reflush every week. Use redline water wetter. While you're doing a flush, pull the thermostat completely out to allow unrestricted flow through the rad. All of this will cost you $50 and several hours, but it *might* work.
It is almost certainly your rad (unless there is a blockage in the air flow somewhere)
At high vehicle speed, lots of air blows through the rad.
The question about the electric fan was more to help determine if the RAD was bad. In moderately warm weather with the AC off it shouldn't come on above 40 MPH.
The cooling capacity of the rad is a function of heat injected vs. the mass and temp of air flowing across it. At highway speeds the air wins due the huge mass per second flowing across it and the thermostat shouldn't need to open all the way. Stopped in traffic in gear, with the AC on, the heat from the coolant will win and the temp will eventually start to rise in every car.
If youre rad is coated inside with limestone/calcium, there is little a flush will do for it, especially if you or the shop is using tap water. The trouble is calcium just doesn't dissolve that easily.
The outside of the rad is important too, as you note, so is the performance of the AC rad - if it's plugged with leaves and reduces airflow that cuts cooling capacity.
Since a new rad for you car will cost $370, you might try a few of the tricks first - flush it with distilled water and cleaner. Run it with just 10% antifreeze and reflush every week. Use redline water wetter. While you're doing a flush, pull the thermostat completely out to allow unrestricted flow through the rad. All of this will cost you $50 and several hours, but it *might* work.
