need some thoughts on this one. most of the time the problem corvettes have is overheating but i have the reverse problem overcooling.

my temperature  guage starts at 100 and goes thru 260. since i bought the car the needle would only go to approx. the middle of the two zeros. i know it works as in the summer when it was really hot and the car idled it would go up and the fans would come on so it would register correctly.

with the problems i have been having with it i came to the conclusion that the computer is reading the low coolant temperature and trying to set the engine for that and it is also reading the heat from the exhaust and trying to set it for that at the same time thus causing a conflict.

i figured my stat was stuck open and today went out and installed a new one. as the car was cold when i did it, when i removed the old stat, sure enough it was open.

i installed the new stat, refilled the system and started the car. after it idled i saw the water flowing and went and checked and my guage was up where it should be.

great. i hurry and wash the car and took it to the regular sunday car show that a sweet shop sponsors. another thing i did was add some injector cleaner to it. here is where the problem comes. i was cruising about 55-60 and my temp guage goes back down to almost the same as when the open stat would go to. if i stop and let it idle it goes back up.

my question is, does anyone have an idea of how to cut down the airflow so it doesn't overcool the engine?

thanks for any input.

dave


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LIFETIME MEMBER #97
THE DYNAMIC DUO

Wow...that's a sucky problem to have on a 'Vette...running too COLD???
I would first want to know if the gauge/temp sensor was correct. My '85 runs around 220 most of the time, but it will cool down to 190 on the road, depending on ambient temps. If BOTH fans are coming on, then the ECM is seeing the temp at least 235/245. Not sure on the '90 where the primary fan comes on, but it should be in the 230 range, with the pusher on at 245 or so.

btw...the ECM doesn't know how hot the exhaust is... it may gather info on the EGR temp, but that is just to confirm if the EGR is working or not.

Anywho...I would suggest, at this point, you get a non-contact thermometer(infrared type), check the engine temps, and compare to the gauge readings. I've never been a fan of electrical coolant temp gauges...rarely see one that is accurate.

Also, be SURE you burped the coolant after installing the new stat...if there is an air pocket in the heads, you'll get some temp readings that will not be correct. It may even show as cool as 100, when you know it should be around 200. The temp sensors must have contact with the coolant to work. Air doesn't conduct heat too well in the water jackets.
And if all else fails, stick a piece of cardboard over the rad. air intake at the front.

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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

just a question here. wouldn't the ecm read the heat by the o2 sensor? as that only kicks in when it reaches a certain temp. will try the infrared thermometer when car is idling but maybe kinda hard to do when i am going 60mph. 
seriously i only use the guage as a guideline and never actually trusted it for an absolute temp. i am as positive as can be about burping it as i watched the flow for quite a bit in the tank before closing it.

here is another thought i had just now. the boiling point is higher under pressure. right now it has a 16#cap on it. if i went to a lower pressure cap would it increase the temp of water?


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LIFETIME MEMBER #97
THE DYNAMIC DUO

IF you go to a lower psi cap, it will puke quicker...not exactly what you're looking for.

The O2 sensors read only oxygen content in the exhaust, not temp. SOME O2 sensors are heated, to allow a quicker temp rise so they work faster. The O2 sensors read all the time, but the ECM disregards them(they will have a "fixed" value) until the engine is at operating temp(Closed Loop). The sensors are just not accurate until they are hot.

As for checking the temp...run it down the road(or around town) until the gauge reads above 200 or so, then stop, and check it. Then do the same after driving on the hwy, and the gauge says it has cooled down. Just another way to compare the temps, and the gauge readings. The gauge may be right on, who knows? But...a Corvette that runs too cool is just, just,...well...COOL! As long as it is staying above 190 or so, it should be fine. Much cooler, and the fuel mixture/timing will not be optimum.

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

one mistake i made was i installed a 160 degree stat as that is what i put in the 75. forgot the 90 the computer controls fan. swapped it out for a 195 stat and let it heat up. took about 20 min+/-. took the car down the road for about 3 miles as it was about 9;45 pm here and temp guage went down to approx 160 and stayed there.

will check further tomorrow when i take it to work and hopefully temp will stay up. doesn't make sense to me as i feel it should have stayed up to 160 with that stat in there.

when i said about ecm reading exhaust temp, i guess i was trying to say what you said joel about o2 sensor only working above a certain temp and reading the egr temp. even though it is not really reading a temp it is sending out the info to work as if the car is a operating temp. hope you understand that one.

one difference here joel is outside temp this time of year. its been down in the fifties at night and unusal for this time of year it has been in the mid seventies during the day. i would imagine down there in texas it may be a little warmer.

as a friend said these things could only happen to me. i bought the gm service manual when i bough the car. went to check info on fans and index says section 8A. flip thru the book, get to 8B, turn back a few pages and get to 7C. my book has no section 8A in it!!!! wonder if all the books were like this or if i got the oddball.

hopefully this will correct the problem.


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LIFETIME MEMBER #97
THE DYNAMIC DUO

My Caddidilac manuals are like that! It references a certain section, but it's not it THAT manual!!! It's in one of the OTHER manuals! It's like reading a really good article in a magazine, and it says "Continued on page 156", and you turn to page 156, and it's a Viagra ad, or sumpthin!

The material that the O2 sensor is made of is basically inert until it gets hot, or at least the older ones are. The newer ones are made form different metals, and the ECM actually reads the resistance, and not voltage, like the older ones(yours, and my '85).

A little warmer in Texas? It's aboot 45 deg here right now!

Let us know how it works out in da morn!

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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

seems to me they ought to just say look in other manual. anyway drove to work today and temp stayed up on guage to not quite halfway. i would guess approx. 160-70. will be able to check exact temp when my infrared thermometer gets here. still can't understand why temp would drop so low with other stat.

another quirk here is the code for egr comes on. thought i might have corrected the problem with the engine temp being up where it is supposed to.

i take the same road to work everyday. i work about 18 miles from home. i am usually cruising at 55-60 and about halfway there the engine light will come on with the code. will do it on the way home too. had to go out tonite and it was approx. 30 miles one way. depending on where i was determined how fast i could go but did hit 55-60 ocassionally. engine light never came on. wonder if car just had to reorintate itself to running right.


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LIFETIME MEMBER #97
THE DYNAMIC DUO

  This sounds like a Good Question for Gordon Killebrew. He is the Guy who Teach's Trouble Shooting School at the Big Vette Shows. If You don't allready have His Troubleshooting Kit then You Need One. All C4 Owners Need this Kit it should be mandatory when You right the Check for the Car. With the Test Kit You can find out what Code Fired off the Check Engine Light when it happens and not whenever You get to a Dealer.  Oh and about the Service Manuel I beleive that You will find the Missing Chapter in the Other Book. If not ask Gordon, As He was the one who Corrected all the Manuels for GM.  His Number is 615-654-2864 I think is Test Kit is about $40 and it will do much more for a C4 than any of those Code Readers. I learned the Hard way. After You have the Kit and still can't figure it out You can Call Him for a minimum Charge and He will Figure it out. Or take Your Car the a High end Vette Shop and they will Call Him,They all do,and Charge You to fix it. Richard......

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My Car...PIC 1     PIC 2