strange / backward overheating issue

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strange / backward overheating issue - lsinlv - 06-28-2007

OK Folks....here's a weird one...Let's see if the great minds here can help me, because, well, I'm stumped:

Car runs perfectly normal in daily driving. I can romp on it and it NEVER goes over mid mark or just below. Now, when I run the a/c the car, after a short time will run hot (3/4 mark). As I drive the temp goes UP, but as I slow down, the temp comes back DOWN. <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" /> Stop and go driving the car with a/c on will run at normal temp, mi-mark. If I drive the car with the a/c on at freeway speeds or above 45mph, the temp goes UP, but will come back DOWN when I slow down and/or stop.

Water pump, t-stat and fan switch, and coolant were all replace a year ago when I resealed the front of the motor. Granted the ambient temps are about 105F+.....

I have verified that BOTH fans are on, and seem to be turning at high speed, and they will "after run" when I stop/turn off the car.

The car is completely stock other than the 85C fan switch and t-stat. The front lower bumper cover is gone (has been since we bought the car), but the engine cover/tray is intact.

I'm not sure what other pertinant info I could give you to help me diagnose this issue. I have the manual but no info on fan speed or amp draw....so I am assuming the are functioning correctly.

Any help is GREATLY appreciated! TIA!

strange / backward overheating issue - ron1688 - 06-28-2007

[quote name='lsinlv' post='37589' date='Jun 28 2007, 09:06 AM']OK Folks....here's a weird one...Let's see if the great minds here can help me, because, well, I'm stumped:

Car runs perfectly normal in daily driving. I can romp on it and it NEVER goes over mid mark or just below. Now, when I run the a/c the car, after a short time will run hot (3/4 mark). As I drive the temp goes UP, but as I slow down, the temp comes back DOWN. <img src="/forum/images/smilies/968/unsure.gif" class="smilie" alt="" /> Stop and go driving the car with a/c on will run at normal temp, mi-mark. If I drive the car with the a/c on at freeway speeds or above 45mph, the temp goes UP, but will come back DOWN when I slow down and/or stop.

Water pump, t-stat and fan switch, and coolant were all replace a year ago when I resealed the front of the motor. Granted the ambient temps are about 105F+.....

I have verified that BOTH fans are on, and seem to be turning at high speed, and they will "after run" when I stop/turn off the car.

The car is completely stock other than the 85C fan switch and t-stat. The front lower bumper cover is gone (has been since we bought the car), but the engine cover/tray is intact.

I'm not sure what other pertinant info I could give you to help me diagnose this issue. I have the manual but no info on fan speed or amp draw....so I am assuming the are functioning correctly.

Any help is GREATLY appreciated! TIA![/quote]

Sounds pretty normal... I just got back from Vegas last week (temp average about 99F). Driving at an average speed of 85mph, with the AC on from Vegas to Sac and back puts the temp gauge at 3/4 mark. During normal driving in the city, it stays at half or just below the halfway mark.

strange / backward overheating issue - lsinlv - 06-28-2007

[quote name='ron1688' post='37590' date='Jun 28 2007, 09:14 AM']Sounds pretty normal... I just got back from Vegas last week (temp average about 99F). Driving at an average speed of 85mph, with the AC on from Vegas to Sac and back puts the temp gauge at 3/4 mark. During normal driving in the city, it stays at half or just below the halfway mark.[/quote]

<img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" /> so runing @ the 3/4 mark sould be considered normal???? wouldn't the additional airflow allow the engine to run cooler, not hotter??? what am I missing here???

strange / backward overheating issue - banditsc - 06-28-2007

[quote name='lsinlv' post='37591' date='Jun 28 2007, 12:32 PM']<img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" /> so runing @ the 3/4 mark sould be considered normal???? wouldn't the additional airflow allow the engine to run cooler, not hotter??? what am I missing here???[/quote]

Take a look at my recent post. http://www.968forums.com/index.php?showtopic=4025

strange / backward overheating issue - PorscheDude - 06-28-2007

You may have some air pockets in the cooling system.

Try bleeding the system. There is a bleed screw next the intake manifold on front on the engine.

strange / backward overheating issue - lsinlv - 06-28-2007

[quote name='smokiemon968' post='37593' date='Jun 28 2007, 10:11 AM']You may have some air pockets in the cooling system.

Try bleeding the system. There is a bleed screw next the intake manifold on front on the engine.[/quote]

if that were true, then why does the car run fine without the a/c???

no, I think based upon the other thread, I will check the grounds, as the additional load may be stressing some loose ground. also, I will go ahead and replace the coolant temp sensor just to make sure....is there a calibrating procedure that needs to be performed (like the old oil cooled P cars)?

Thanks again for all your input. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />

strange / backward overheating issue - flash - 06-28-2007

i would get a laser temp guage and check what the temps really are - you could easily have a faulty sensor

while not a new issue, i would also get that front apron back on there - it dramatically affects the running temps, especially when the ambient temp is high, as higher temp air is less dense, thereby exacerbating the high pressure/low pressure zone issues, and therefore the effectiveness of the radiator

strange / backward overheating issue - rustech - 06-28-2007

I have had the same problem for as long as I remember owning my car. The car runs perfect with out the A/C on. I am actually a windows down kind of guy, and so have never bothered trying to fix it, but is definately an A/C problem. My compressor actually cycles a bit as well once it runs for awhile and so I may try draining the freon and recharging to make sure the pressure is set ideal and that it has the proper amount of oil.

It's not the gauges. I don't believe it to be voltage/grounding related. It is not air in the system. Running with the A/C at idle, should not be running cooler than at speed.

strange / backward overheating issue - Rutger Gert-jan - 06-29-2007

"Running with the A/C at idle, should not be running cooler than at speed"

When I switch my A/C on, one fan starts running, so this might be the reason that the car stays cooler when on idle?

Rutger

strange / backward overheating issue - PorscheDude - 06-29-2007

[quote name='lsinlv' post='37595' date='Jun 28 2007, 01:46 PM']if that were true, then why does the car run fine without the a/c???

no, I think based upon the other thread, I will check the grounds, as the additional load may be stressing some loose ground. also, I will go ahead and replace the coolant temp sensor just to make sure....is there a calibrating procedure that needs to be performed (like the old oil cooled P cars)?

Thanks again for all your input. <img src="/forum/images/smilies/968/biggrin.gif" class="smilie" alt="" />[/quote]

It would only take 2 minutes to verify that there is no air in the system. And this is free

strange / backward overheating issue - rustech - 06-29-2007

[quote name='Rutger' post='37623' date='Jun 29 2007, 01:34 AM']"Running with the A/C at idle, should not be running cooler than at speed"

When I switch my A/C on, one fan starts running, so this might be the reason that the car stays cooler when on idle?

Rutger[/quote]

Both fans are always supposed to turn at the same speeds whether off, low speed, or high speed. When the A/C is pressed, both fans are always supposed to run at high speed. (The fans obstructing the flow is one theory at this point, but why it doesn't effect everyone is what would need to be determined.)

Regarding air in the system, it's really not the issue. Everything in my cooling system is new and top notch. If it was cooling related, it would do it under increased engine load as well. We'll get to the bottom of it.

strange / backward overheating issue - lsinlv - 07-02-2007

<img src="/forum/images/smilies/968/mad.gif" class="smilie" alt="" /> found it!!

it looks like the heater control valve had a very small leak....so small I could not see it, nor smell it? <img src="/forum/images/smilies/968/blink.gif" class="smilie" alt="" />

the valve officially blew on my way home this afternoon.....not fun in 115F weather........logic dictates that the lack of sustained pressure under higher thermal load, caused the partial overheating.

it got to the red, and I did stop quickly to cool it off ASAP. my hope is that all is fine with the head and head gasket.

will update once I get the necessary parts..... <img src="/forum/images/smilies/968/mad.gif" class="smilie" alt="" /> Vegas is still hard to get import parts in.....35 years later....

strange / backward overheating issue - flash - 07-02-2007

bummer - glad you found it though - a leak is definitely going to do that - same thing with a weak reservoir cap

strange / backward overheating issue - lsinlv - 07-09-2007

<img src="/forum/images/smilies/968/angry.gif" class="smilie" alt="" /> well....after the repair, with new hoses, heater valve, cap, coolant, and water wetter; it SILL runs hot. better than before, but still hot.

I am not the daily driver of this car, the wife is...but she did confirm that last year, during summer it did NOT run hot. so, at this point, I think I am going to pull the radiator and have it cored/cleaned...and if that is not it....not sure where to look. I'll be doing this in about a month or so.

I'll keep all posted.

strange / backward overheating issue - banditsc - 07-09-2007

[quote name='lsinlv' post='38025' date='Jul 9 2007, 11:22 AM']<img src="/forum/images/smilies/968/angry.gif" class="smilie" alt="" /> well....after the repair, with new hoses, heater valve, cap, coolant, and water wetter; it SILL runs hot. better than before, but still hot.

I am not the daily driver of this car, the wife is...but she did confirm that last year, during summer it did NOT run hot. so, at this point, I think I am going to pull the radiator and have it cored/cleaned...and if that is not it....not sure where to look. I'll be doing this in about a month or so.

I'll keep all posted.[/quote]

If it's still keeping not overheating while it's idling in traffic but only at speed, then the radiator is probably not the issue. The radiator would be working the hardest when it's at idle with no air from the front blowing thru it. Pull all the ground and clean them up, also check the if it tends to run hotter with the A/C off and the Lights on, vs A/C off and lights off while you are driving. I ran into this also and figured it was the added electircal load like the A/C was causing. I noticed it ran warm when driving at night with the lights on, when it should have been cooler in the night air.

strange / backward overheating issue - lsinlv - 07-09-2007

I am begining to think the hoses let loose/burst under high pressure during the high temp run....I have not found any tears/holes in them...but the valve is suspect.

as for gournds, I will give them a look, as well as the headlight vs. a/c test.

I have an IR gun so I will check the condensor and radiator for any hot-spots. again, I am not sure that fans are running "high speed", but they sound to be doing so.....

strange / backward overheating issue - 968rz - 07-10-2007

If it runs hot at freeway speeds then its not the fans (but you should check them), they really shouldn't come on much at all then (should with a/c no matter what). I would keep looking for another leak and re bleed the system (twice just in case <img src="/forum/images/smilies/968/wink.gif" class="smilie" alt="" /> ). Word is these can be stubborn and hide air in the heater core and such (btw-you should have the heater on hot/no fan when bleeding). Hope this helps.

strange / backward overheating issue - unknown4u - 07-12-2007

I would replace the themostat and check the temp with a lasergauge.

The problem you describe seems to be an half open thermostat. I think it is broken.

Better to replace it before trouble gets worse

strange / backward overheating issue - banditsc - 07-12-2007

[quote name='unknown4u' post='38131' date='Jul 12 2007, 08:45 AM']I would replace the themostat and check the temp with a lasergauge.

The problem you describe seems to be an half open thermostat. I think it is broken.

Better to replace it before trouble gets worse[/quote]

That was one the first things I replaced and it didn't do anything for me. I was driving last night and it still seems to be running hot when the lights are on, maybe it's just the gauge with the added electrical load. It was dark, so no sun, high 80's running at highway speeds and the needle was inline with the top white line, the battery gauge was also right at 12 volt. I think I have seen some peoples gauges show higher volts then that. Starting wonder if the alternator is getting worn and causing a higher load on the engine while it tries to keep up with the high load items like lights and A/C. The battery seems fresh and it's the proper size. If it was daytime in full sun in the high 90's at the same speeds the gauge would have been half way between the two whie marks.

strange / backward overheating issue - flash - 07-12-2007

there was a recent case of an alternator dragging that ended up breaking the ac compressor

i would pull the belt and give her a twist and see if that bearing is bad to rule that out as a cause

normally lights and such should not make it run hotter

it sounds more like you have a wiring issue or sender issue generating an inaccurate signal, exacerbated by the increased load - a bad dash ground would do that

i would definitely get a laser guage on it to see just how hot it really is