What temps does your car run at during the summer? I ask this because I'm not happy with how hot my car runs while running the AC. The digital gauge I believe is very inaccurate (it was saying my engine temp was only 142' while the analog gauge was 3/4 to the over-heat mark, and when I shut the car off, the water in the over-flow was boiling). My car, during the winter, runs at the 1/4 mark on the analog gauge. During the summer, without the AC, it runs at about the half-way mark on the analog gauge. But if I run the AC, it will heat up to the point that the analog gauge get to over the 3/4 mark, at which time I shut off the AC so the engine will cool back down to the halfway mark. I know the LT1 is designed to run hot, but so hot that when I shut it off, the water in the over-flow is boiling? What does the analog gauge of your LT1 Vette show?

I've checked my radiator to make sure it's not cloaked with road trash. If need be, I can post pics of my gauges while the car is running the farther explain what I'm talking about if need be.

 

radiator needs to come out to be cleaned properly. That and a new thermostat will most likely solve the problem

 

Mine has been in the 230-240 range and is within 15* of the anolog gauge so new water pump, aluminum radiator and knock sensors are coming. Car has 110k and I know nothing of the PO history of maintenance except my detailed log since getting the car last October. My outside radiator and condenser are free of debris.

 

How high does your analog gauge read? Mine doesn't have any temp readings on it. It just has 3 marks on it (1/4, 1/2, 3/4) quartering it up like a analog gas gauge. Does yours also run over 3/4 up with the AC running?

Oh, something I should have included in my opening post, I don't know how high the analog gauge will go with the AC on as I'm unwilling to run the car with it over the 3/4 mark. So I don't know for sure if the car would actually overheat while running the AC.

 

You may have an air pocket in the system or possibly a radiator hose collapsing. When was the last time the coolant was changed? Have the radiator hoses been changed? Is the pressure cap new?

It's certainly possible that the radiator and A/C condensor are clogged up with dirt and debris. You can vacuum off some of that stuff from the front and use a garden hose to force dirt from the back side of the two units.

Running the A/C should force both cooling fans to stay running. Do both run?

The analog gauge is not that accurate. The digital gauge will be a much more accurate indication of the coolant temp.

 

I live in Alabama and right now it is hot as hell (95-100 with 100% humidity). During the heat of the day my digital gauge runs between 210-230 or so depending on if I am just sitting in traffic or not, which I usually avoid the traffic most of the time. In the morning when its in the 70s it reads 180 - 200 or so.

 

Coolant was changed the beginning of last winter

Radiator hoses showing no signs of collapsing

Pressure cap is not new. Don't know how old it is. Seems to be working properly.

Radiator has been in the car less than a year, and it was thoroughly cleaned before installation. Visual check revealed very little debris between the evaporator and radiator, which was removed.

I don't know about the fans, I'll go check in a few minutes.

My digital temp reading is way off. I had water boiling in the over-flow with the analog gauge showing 3/4 up the scale, while the digital reading only said 142'.

 

So this high temps/boiling is something new? The early LT engines have two bleed valves that help with removing air from the cooling system as it gets filled. One is on the thermostat housing, the other is on the throttle body. These need to be open when filling the system. Once coolant starts to come out, they are then closed and the remainder of the coolant is put it.

142 degrees sounds like the coolant temp sensor is not working properly. Might want to replace both sensors.

 

It's not new. I'll try bleeding the cooling system when I get a chance.

I checked the fans, only one fan comes on when the AC is turned on and the car is first started and not at running temps. I've got the car warming up now to see if the 2nd fan comes on after the engine warms up.

Also, when I turned on the ignition, before even starting the car, the digital temp showed 142', so yeah. That sensor is definitely bad.

 

Cars run pretty hot today. They're designed to do that.

Most of us worry too much about our temperatures. In discussions with several engine builders and radiator manufactures there was agreement that it’s best to run in the 210 to 220 range. Even 240 is not a problem under the right conditions.

We all know that water boils at 212 degrees so how do we get above that boiling point? First we pressurize the system. We do this with the radiator cap. Every radiator cap has a pressure rating. Each pound of pressure in the cooling system raises the boiling point by 2 to 3 degrees.

If you have a radiator cap that allows for 15 lbs. for pressure your coolant won’t boil until it reaches 250 F. If you use a cap rated at 20 psi you raise the boiling point of the coolant to over 270.

Here's an article I wrote about all of this last year.

Richard Newton

 

Well, try to fix one problem, find 2 more. Looking for the bleeder valve on the throttle body, I saw that the fitting for the vacuum line to my FPR has come apart. And then, looking at that, I noticed gas spitting out of the FPR. Work shift starts in about 3 1/2 hours, so it looks like I'm going to NAPA this morning and replacing the FPR and vacuum line tomorrow morning.

 

The digital gauge is normally much more accurate than the analog; if you are getting readings of 142 you need to have it fixed, that is impossibly low. As for the analog gauge, it is not linear, so that 3/4 of the way up the gauge does not extrapolate to a temp of around 240 (I'm looking at a 94 gauge). So, you may not really know how hot you are, but you shouldn't be boiling. Check your coolant and make sure it isn't just water, then get your digital fixed and see what it says. And remember that in some situations temps in the low 230s is as designed.

 

coolant in the overflow is not under pressure and may boil above 212* depending on coolant mix. If your pressure cap opens at 15lb you'll be letting coolant at about 240* out the overflow and it may boil.

 

...then we add coolant at a 50/50 mix (typically) which also raises the boiling point.

I have to laugh when people cite a specific temp that "its best to run at"...with no further details. Best for WHAT? Different operating temps have advantages for different situations or criteria. I don't think that a 10* range exists that is "best" for all engines/all cases. Lets remember that the OEM had to meet different criteria than most of us need to or care about.

Regarding the original question, your operating temps aren't acceptable, IMO. Yes, they may be in the "operating range", but so is 10 PSI oil pressure at idle, and I think most would agree that 10 PSI at idle isn't typical/normal. Your temp gauge at the "3/4 mark" isn't normal or typical for a properly functioning cooling system.

First thing I'd do is fix the Digital read out (sending unit, most likely) because it's very difficult to get meaningful data from the gauge -it behaves more like a "Cold-Normal-HOT" switch.

Then, I'd back flush the radiator fins w/a garden hose, then I'd change the cap (cheap), then I would flush the cooling system entirely. I doubt that it's the thermostat, since it appears to run at the right temp w/the AC off, but it's possible. They're cheap too, so flushing would be a good time to change it.

My '92 runs at the "1/4 mark" on the gauge, or from about 185-195 most of the time in the summer, AC on or not...25-35* colder than the "best temp", apparently. It will actually get hotter w/the AC off, if I'm sitting or driving slowly since the fan doesn't turn on until ~230*F.


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Just cause it looks clean from the top doesn't mean crap is no deep in the fins,or some of the tubes inside the radiator could be clogged.

 

Yes mine same as yours creeps toward the 3/4 mark and has been over that with AC running, I did a flush last October when I bought it but didn't take out the knock sensors which I should have so this time, new aluminum radiator, water pump and knock sensors. I replaced all hoses and thermostat last year. I believe this will keep my cooling inline and can use the car in a few parades.

 

Anyone have a good write up on how to chance the thermostat?

 

On my '96 so far this season (since new hoses, WP, Thermostat, coolant, KS, temp sensor) Ambient temps in the high 80's in traffic with A/C. Digital gauge reads 197F. Analog in lower 1/3rd.

And I put in the wrong thermosat (195F).

So I will be doing a thermostat swap before the real heat kicks in.

 

I took a pic of my track car on the street yesterday. Oops trans didn't register, it was 142.


If your water temp gets over 120 you're going to break it!

 

What year C4 is this post about? Is that trans. temp your seeing? Or coolant temp.?