Cognac510

How did your mechanic determine you have a leak in the heads? Did he pressurize the cooling system or test the cylinders or what?
On my 86 highway temps are around 184-189. Around town (typically stop and go) temp can get up to 229 before the fans kick in then it drops below 210~.
If your cooling system is topped off and temps stay in that range, I don't think you have issues. If you have a/c on the car, if you kick that in it kicks the fans on the newer ones and I suspect yours is the same.

If you have the radiator cap off and the thermostat open, see if you have a stream of bubbles in the coolant - not good. Typically that's the indication of a blown head gasket. If you're concerned, do a pressure test of the cooling system and a compression test of the cylinders. If they hold pressure, it's not likely you have a blown gasket or head thought nothing is 100% other than death and taxes.

 

with the rest
these always tend to heat up some at slow/stop normal

to design a car to run to 240 before the fans kick on is rediculous, very little margin for error there. Is what it is

 

To answer ACAR94's question earlier...

All the 92 and later C4's are not the same. In the mid 1990's the Federal Gov't was forcing all the automakers to go to the OBDII protocol - and those changes occurred in the middle of the 2nd part of the C4's run.

So - in 1992 & 1993, and from what I believe most of 1994 cars - if you want to alter the PCM programming the only way to do it is to pull the actual "EPROM" chip out of the PCM, and physically use special equipment to write a new "program" to it, you can't do it through the underdash port like you can in newer cars. By 1996, the C4 had the OBDII system, and you could "reflash" the PROM via the OBDII port - making is significantly easier to set what temp the fans come on at.

There are people here who know more than I about the protocols - but the late 1994's and 1995's are sort of a mix between OBDI & OBDII, on a friends 1995 - he had to pull the chip to get new parameters programmed in the PCM. I've hears some of the later 1995's had the full OBDII functionality.

So - if you have a '92, '93 or '94 and want to alter the fan settings - plan on pulling the PCM and sending the chip out to a place that can re-program it for you. Alternatively - on any post '92 C4 you could splice a switch into the wiring to the relays that control the fans, and manually turn the fans on when you want (say in heavy traffic when the temp starts to rise). Later C4's that have full OBDII functionality are easier to program - it can be done via the OBDII port - but the equipment to do that will cost you several hundred dollars, so you might want to visit a shop that does tuning, and can buy additional licenses for their reprogramming software relatively inexpensively.

 

First I would like to thank you for responding to my questions. My mechanic claimed he did the pressure test and there was/is to much pressure built up in my cooling system but my car is running great just like yours but I did notice my overflow was full which was weird to see after it was completely empty when I checked what my fluid levels were before taking off the other day. I have looked into how to resolve the absurd design these cars have with running hot and I am going to try to have a sensor put in which will allow me to control the temp at which the fan comes on. On the freeway I have seen 160 temp readings and my fluids haven't leaked out since I have been checking them everyday before I take lee-vette out the garage. This is my first corvette and I worry about her temp since I live downtown sf and there is constant traffic but I am learning to trust her cooling system and grateful that I got my a.c. repaired. My next "move" will be having the sensor/switch put in by a different mechanic inexpensively because the last mechanic was just trying to milk some more money out of me

 

you have a problem there. u have a leak somewhere. the system heats up, whicch expands the coolant and it goes out to the overflow. the system issnsupposed to be closed. when it cools, the system is supposed to creare a vacuum and suck that fluid back in from the overflow res.

you have an issue, these cars cool just fine when the systems as functioning as designed. some things to check:

1. check the hose from the rad cap to the overflow. cracked? leaking? atmosphere is leaking in somewhere.

2. check your rad cap. the TOP seal on the cap could be bad and allowing atmophere to enter during the cooling phase (sucking back in phase).
3. check your heatercore. run your heater full blast. smell coolant? put it on defrost, get fog on windshield?

4. check for seepage at the intake gasket in the valley, specifically back towards the distributor

check those and report back.

i actually believe your mechanic if your res fills upmand never sucks back. even once, u have an issue. mine was heatercore on my 87 and head gasket on the 85.

 

so my solution ended up being that adding a sensor/switch to have my fan turn on sooner and now my temperature flucuation issue is over. i am going to look into seeing if i have any leaks still. thanks for the advice

 

use a turkey baster to take the fluid out of the overflow. put it back in the rad.

if it fills the overflow again, and doesnt suck back in, u have issues. your earlier fan setting may take care of the symptom but is most certainly not fixing the source of the symptom.

keep us posted.

 

Here's a couple of things that may be of help.

If you use the Prestone yellow/green antifreeze, try using a black light. I found that it will fluoresce under black light. You might find an external leak that way, even stuff that's not currently leaking may show a trail.

If you have an L98, there's a U shaped hose on the front of the engine between the TPI and the front of the block. When I had a leak issue, it turned out to be that hose that was the cause of the leak. It was impossible to see because it was hidden so well and it's behind the water pump.

 

LT1 are reverse flow thermostat lets cool water to enter engine from radiator not from engine to radiator.

 

On my '87 L98, I fill the system by first filling the radiator, then putting the cap back on, I fill the rest via the heater hose.

I have a 160deg thermostat, and a fan controller that kicks in at 175deg. Normal running temp is about 185deg. The radiator cap has a lever to burb out any air.

One time when all was stock, the fan failed and the temp shot up to a red 260deg+ in seconds. The fan is vital to keeping things cool and you have no warning of impending doom when it fails.

I don't care if the C4 runs that hot as normal, as its little comfort when your radiator boils over and blasts glycol steam out of the expansion tank like a WW2 fighter with a radiator hit. If you want to run that hot, fit a warning light to tell you the fan has failed as your close to blowing/warping heads at that temperature and very quickly too.

 

Thought you might enjoy the fruits of my labor from many years ago !

 

Cruising temp 180-190

Stuck in traffic i get 234 as maximum, after that, fan starts and put temp down.

When do you get 217? Lt1 cooling system is self purging anyway, if anything can hold the pressure (no fracture in tank, radiator, good conditions hoses)

A thing that you can do to get air trapped in, is to run till when you reach operating temp and open 2-3 seconds air bleed valve on t stat housing (put a rag under it in order to not soak optispark in coolant, even if for 1996 shouldn't be any problem cuase it shoul be a sealed unit)

You had to make three-time cooldown before to get out any air trapped in, and before to hit high speed