ohlins8990

Car is a '99 C2 6 spd

Trying to get the car ready for track days and the coolant temperature is something that is still bothering me. I am usually in the low 90's for temp on the A/C hack when traveling on the highway, but when vehicle speed drops below 40 or so, the temp creeps up to 100-105C. All in mid 80's (F) ambient temperature.

I have a new thermostat, waterpump, new fan relays, and have pulled the bumper and cleaned the radiators. Both fans are working and on both speeds. Low is on from the get go since the A/C is on. High is coming on at 103C, but doesn't appear to do much as far as cooling the car down any. I had originally seen temps up to 108C before doing this work, so there has been some progress in the right direction, but the last thing I want is to overheat the car doing a track day.

Interesting to note is that 103C on the A/C hack is 210F on my OBD scan tool. Right now I am telling myself that I'd turn the car off if I got above 110C on the A/C hack or the needle crossed the mark between the 180F mark and the end of the gauge (looks to be 225F or so). Does anyone know what else I can be checking and what temperature does the car turn on the overheat light on the dash?

Slakker

That's about what mine runs. Sounds pretty normal. Did you upgrade to a low temp thermostat when you replaced it? Those are highly recommended.

Also, if the light starts blinking, it doesn't necessarily mean overheat. It can be coolant low or ambient engine temperature. Mine started blinking when I first got my car right as I was pulling into the driveway. I shut it off and towed it up to the garage. Only to be guided by forum mates to figure out my ambient engine temperature sensor had come loose and was sitting on the engine. PO had taken it to the dealership and they said the car was just cranky. Rennlist solved it in under an hour.

NickHolloman

When warmed up, my car lives with the needle between the 8 and 0 of the 180 degree numbers, so I'm guessing I mine stays about 182° F under normal conditions.

I live in Alabama where it is miserably hot.

johnireland

Same here in California with a 2000 MY cab.

speed rII

Have you tested the temp sensor? When car is cool, check that the temp reading is close to ambient.
Or remove sensor and heat it to 90c and measure the resistance.

My car hardly never runs to 90c in traffic or track. Usually temp is 80c and stays there.

CarlOrton

My '01 C2 normally runs the same as Nick's. Between 8 and 0. That's with a/c off. When I come to a light after getting on it, it will creep up to the center-right of the middle of the "0", but then the fans kick in and it comes back down.

NickHolloman

identical to mine. Good to know. I watch it constantly

KNS

Keep in mind that the water temp your'e seeing on the gauge are a "general" reading. It's not unusual for the temperature to fluctuate up and down somewhat but the needle won't budge.

DreamCarrera

Check to make sure both of your radiator fans are operating at both the low- and high-speed settings.

I'm surprised that your a/c unit hack is reading that far off the mark from the OBD scan tool reading. Other comparisons I have seen have been closer between the two. Maybe your sensor is shot?

Overall, I think your temp reading are pretty normal. The 996 runs very warm...

+1 The analog dash gauge is just a "dummy" gauge. It does not give you an exact reading by any means.

CarlOrton

Agreed. I used a Durametric to check the sensor temps and saw them vary +/- 5 deg C with fans kicking in and out. About the highest I've seen is 100 C (plus a low fraction) or 212 F. That's before fans kick in.

ohlins8990

I'm going to replace the coolant temp sensor. This morning the AC hack was showing 27C(81F) when outside temp with my phone was 68F. This was right when I turned the car on. I appreciate all the feedback, hopefully this clears up the issue.

ohlins8990

Update-

Coolant temp sensor replaced, readings between the AC hack and scan tool are a bit closer, but the scan tool is still reading ~5F lower when I went for a drive today. I was still able to get the AC hack to read over 105C when I did the "air bleed procedure" after changing the sensor. The fans managed to get the temps back down below 100C with it just idling afterwards, but it was a pretty mild 75 degree day and have little faith that the system would keep the car cool if it was properly hot outside.

I can't see a low temp stat fixing this issue. I could see how a third radiator might help a bit, but the car stays plenty cool when it's moving, just stop and go below 40 mph is a problem.

Slakker

Low temp t-stat is recommended regardless.

ejdoherty911

this is what my temp gauge reads when hot, I had been driving for about 45 minutes at this point in 81 degree heat.

ohlins8990

ejdoherty911, Are you running a low temp stat?

Do most people here run 50/50 coolant/water? I suppose I could thin out the coolant a bit to improve the thermal conductivity, but I like knowing I'm well protected for the days its -15F in the winter.

Slakker,

Here's my issue with the low temp stat. If the cooling system was operating properly and had no issues keeping the car between the full closed/full open range of the low temp stat (say 160-180 degrees) there would be no issue for me. What I do not want to do is open the tolerance of the engine's operating temp. I do not want the engine to run between 160-220 degrees. I am guessing that the OEM stat is full open at 200-205 degrees since Pelican has it listed at 180 degrees opening.

I could understand hitting 210 degrees or so a hot day (100F) in severe stop and go traffic. But hitting close to 220F on a mild mid 80's day either says the system is undersized or that it's not operating properly. I'm leaning towards the latter since the majority of the posts here are saying their cars never go above the 190-200F mark.

The question is what is not functioning...I have eliminated the water pump, thermostat, dirty radiators, fan operation, and the coolant temp sensor. Seems to me that the only things left are clogged tubes that are lowering coolant flow through the radiators.