Background:

1994 LT1 with 62,000 miles, recently purchased with no history on the car.

Driving home today in traffic I looked down to see my temperature guage (needle, not digital readout) quickly approaching the maximum limit of 260 deg. I pulled into a parking lot, popped the hood and check my reservoir. Everything seemed fine. So I started the car and hit that 'guages' button to get the digital readout on temperature and continued to drive home......due to the fact that traffic somewhat cleared out and I kept moving, the temperature remained under 200 deg. I was somewhat surprised how quickly the temperature came down from the 250 deg level. The engine was not turned off more than 5 minutes.

When I got home I sat in my driveway and watched the temperature guage. Sure enough after about 3 minutes the needle started to steadily climb toward the maximum of 260 deg again. However, the digital readout was significantly less......... I am guessing that the dial went to about 250 while the digital readout never got above 215 deg.

I just got the car about 1 month ago. The previous owner had installed two switches on the center console that turn both fans to cool the radiator.

So, I turned both fans on and IMMEDIATELY (much quicker) than I would ever expected, the dial backed down.


Issues:

1. I have a hard time believing that the water temperature can drop that quickly.....so what is happening? Bad analog guage? and digital is ok?

2. I tend to believe the digital readout over the needle.......is there a way to confirm either guage?

3. The car has 62,000 miles on it. I have no history on the vehicle and no way of finding out. I am thinking it would be a good idea to do a complete engine flush as a good place to start.

4. Could it be as simple as a stuck thermostat?

5. I seem to remember reading that these engines do run hot. What should I expect the water temperature to reach while in traffic on a hot day?

Thanks

K.C.

 

When I had my 92, I never relied on the analog gauge. The digital gauge is more accurate and the sender is what provides input to the ECM for fan operation. I always had the digital temp displayed, and moved through the other selections as needed.

Later C4's are designed to run hotter for helping with emissions. If the cooling system is in good shape, normal operating temps will run from 195 to 220 or so. The secondary fan doesn't even come on until 228 degrees. My 92 would see 225-230 in city traffic on a hot day but the temps would drop as the secondary fan started.

Oil temps will typically be 10-20 degrees hotter than coolant temp.

While the prior owner may have wanted more control over the cooling fans (the switches), as long as the system is working, there is no real need for manual fan operation.

If you don't know when the cooling system was last serviced, it might be worth doing a cooling system flush and refill and maybe new upper and lower radiator hoses.

Also check for dirt and debris at the front of the A/C condensor and radiator. It's easy for stuff to build up there as all of the cooling air comes up from the opening behind the front plate. Dirt, debris, leaves, plastic bags, road kill, Honda's, can all get caught up in there and cut the flow of air to the radiator.

You can clean that out with a vacuum from the front side or by directing a stream of water through the fins from the radiator side. Chances are you will get a lot of dirt out from between the radiator cooling tubes and fins.

 

I have the exact same car and it does the exactly the same as you described. That is their normal operations.

I went through the same questions you have and was told it was normal. I replaced the water pump, thermostat, and radiator. It was all for not.

My car is is the shop right now but as soon I get it back, I am installing a switch for the fans. I just don't like it getting that hot and waiting for the fans to come.

By the way, if you turn the AC, the car will actually run cooler because the fans come on earlier.

 

I think you solved my problem. I park both my '06 Honda Element and the Vette in the garage and yesterday the Element was suspiciously gone and that is when the Vette overheated.....thanks.

Interesting to me is that I have had the Element for about 1 year and always like it......good, common sense car with good mpg.....but now after having the Vette, it is quite a change to go back and drive the Element and I like the difference.

 

I got so caught up in responding about Honda cars that I forgot to ask the question!

Are you saying that there are two temperature sensors in the engine. One for the digital readout and another for the analog needle (I assume all needles are analog) on the instrument panel?

And that the sensor that feeds the digital readout is the sensor the feeds the ECM.......

Last night when submitting this thread I assumed one sensor with a tee on it to send the signal to two different places, but about 0500 hrs this morning started thinking that maybe they were separate sensors......

The implication here is that the needle on the dash is bad......and for some reason responds immediately when turning the on the blower fans manually from my console and then agrees with the digital read out ......which makes me wonder if there is any EMI issues resulting from when they wired in the aftermarket fan switches?

 

Thanks for the input.....so does your analog guage climb quickly to 250 deg while in traffic and the digital reading only goes to about 215?

When replacing water pump, thermostat, and radiator, how difficult was the job? I have seen a lot of good threads on flushing the cooling system and may get that done as a precaution, as well as clean out the area around the radiator.

When this happened to me yesterday, the outside temp was in the low 50s.....so it was rather cool and I was not sitting very long at idle.....I have only had the car for about a month and it is my first Vette.....so I am still low on the learning curve.

 

I have a 92 lt1. These engines are designed to run hot. Do an advanced search and you will hear both sides to the issue. I installed a new chip by Hypertech which tells the computer when to turn on the fans. The chip sells new for about $100 bucks and is easily installed. This is a much easier solution , rather than changing your waterpump etc. Its hard to believe the engineers at GM are wrong, but I'm not comfortable with fans coming on at 228 degrees. The chip plugs in easily and can be removed at any time..about 15 minutes...Some claim lowering operating temp will not allow moisture to be removed from oil. Just completed intake gasket and valve covers replacement. My engine was clean inside. No problems with passing emissions either. You can have the chip guy program any temp you want . 180- 190. Mine is set a little low...Jim

 

My analog and digital guages match with 5 degrees. As far as flushing, there are threads which show and tell you how to flush every part of the motor, heater, etc. I just pulled the plug on the radiator after it was warmed up to enough to open up the thermostat and I also left the heater on. There is also valve on the top of the thermostat "housing" you can open. This isn't perfect but was good enough for me.

I would take the time to pull the radiator and see how plugged up it is. For $200, you can a brand new radiator shipped to your door from GM Parts Direct. There are also nicer radiators that have more cooling area from Ecklers and probably other sights.

I planned on adding a switch for both fans when I get my C4 back from the shop. If one can get a chip for $100 that turns on the fans early, that might be cheaper way to go. I haven' looked into that route yet.

I think if you turn on your AC, the temperature should stay much lower since the fans will turn on earlier due to the pressures measured in the AC line.

 

Your 94 doesn't use a chip. The PCM will have to be reprogrammed to change the fans settings.

 

As STL94LT1 said, you don't have a chip but it's even better for you as you can hook a laptop up and change the temps in the PCM yourself. I lowered mine last year this way.

Either that or like you said, turn on the A/C which will turn on both fans.

 

Do tell! What cable and software did you use to accomplish this?

 

K.C.E. in short, your car did not overheat. Welcome to the world of LT1. Your system is normal and working fine.

 

And the analog gauge is not linear.

 

http://tunercat.com/

http://www.akmcables.com/ccard.htm

 

I agree. It's normal for the analog gauge (the one with the needle) to close in on the hash mark area of the dash gauge when the engine is left idling for extended periods or caught in traffic and the A/C off.
Don't sweat it (pun intended), LOL.

I also agree that the analog gauge isn't linear, so although it "looks" like the coolant temp is right near 260F, it really isn't.

Yes our cars have two coolant temp sensors. One's in the passenger side cylinder head. It's the one that the dash uses. The other one, the one the PCM uses, plugs in the front of the water pump.

Since summer's about to kick in, now would be a good time to check for any debris (leaves, paper, etc.) in the radiator area.

As they say in "The Land Down Under" NO WORRIES.

Jake

West Point ROCKS!

 

So I spend a couple hundred on cables and software, have to relearn assembly language, and figure out where the values to change temperature on/off, and reflash an eeprom and hope it works. That is not for the faint of heart. Can one just buy a burned eeprom with temperature values changed and replace it?

 

You can ship your PCM to Bryan at PCMFORLESS and he'll tweak it and get it back to you in a few days.

Not only can he change the temp that the fans turn on/off, the can modify the fuel and timing changes and other things as well.

I had him do mine on a totally stock 96 LT1 and the difference was amazing. As soon as I turned the key and fired the engine I could tell how much sharper the engine responded.

I feel it's best to let someone who knows what he's doing fool with the programming. I've thought of learning to do it myself, but came to realize that some things are best left to the gurus.

Money well spent.

Jake

West Point ROCKS!

 

Tunercat is free for something like 20 uses. You need to pay 20.00 for the Y body file from them. There's no assembly language as it's a Windows program and you can click checkboxes or edit some values right within the program.

As for the cable, look around. I got mine for 60.00 last summer (I can't remember where). So for a total of under 100.00 you have everything you need to program it yourself. It takes 5 minutes to make any changes.

It's invaluable as you have a code reader, a code resetter, a programmer all in one with the cable. I can't imagine any Corvette owner not having this.

So far I've disabled the skip shift and lowered the temps that the fans kick in. Just the cost of a CAGS eliminator for the skip shift is around 20.00 so to me it was money well spent.

Seriously it's easy and inexpensive.

 

Hook a laptop up to the PCM? Raises several questions.

1. Since I just got the car I do not know where the PCM is located. I can look around or check FSM or you can tell me?

2. The PCM has a serial port? Too old for a USB? or,....

3. Do I need to buy a special cable to go from my computer and PCM?

4. Do I need special software?....or go into DOS mode and see what happens?

Almost sounds like an OBD scanner tool function?

Any info on this would be appreciated.....or link to a thread....I will do an advanced search in the mean time.

 

You can get the cable here.

http://www.aldlcable.com/sc/details.asp?item=aldlobd2u

The tunercat site is confusing. I can't tell what I would need to get.

I tried several different software packages and could not get any of them to work but maybe something was wrong with the PC I was using.

I was looking at a TechScan 7000 but do not know if it will program the PCM. I emailed them to see if one could do that. Plus it will work on my other ODBII vehicles. Here is its link. You can get it cheaper on Amazon.

http://www.autoxray.com/product_detail.php?pid=136