Brenden Rogers

The coolant temp was about 255 when I noticed the increases in the oil temp. The oil pressure stayed high throughout. (it was more than half way on the oil psi gauge)

don hall

Based on the symptoms presented, I think the head gasket has ruptured, allowing exhaust gas to enter the cooling system. The exhaust gas super heats the coolant immediately, and increases the pressure which will exceed the rating of the cap rapidly, and force coolant to the overflow bottle. The internal pressure negates any return siphon to the reservoir.

If you are not filling the reservoir each time you run the engine, the cooling system will be out of coolant shortly.

The rapid increase in coolant temp is directly related to the increase in oil temp.

!. Have you tested the coolant for exhaust gas?

If the head gasket is "blown" - "ruptured", a new radiator will not solve the problem. Bleeding air/bubbles from the cooling system will not help.

Confirm that exhaust gas in in the coolant. If so, replace both head gaskets.

Buccaneer

WOW! I would also be concerned with the heads, warping that is at a temp of 290*, that isn't good. If the head gasket is blown, I would definitely have the heads checked by a good machine shop and check for any debris trapped in front by cooling system and replace rad if needed. Good luck and post results.

jmgtp

Seabright makes good points above. If you do end up replacing the HGs, once the work is complete validate the integrity of the cooling system before running it. It's possible that the HGs were not the cause of the overheating but a symptom. Back when this happened to me it was the radiator which leaked and allowed air in. The result was a motor that overheated and bowed the heads a bit. Speaking of - if you do the head gaskets have the heads checked out to make sure they are level.

Keep the info coming, let us know what you find.

Brenden Rogers

Ok, so I'm going to just spit out a bunch of information here:

I was doing a block test on the car when I noticed this, both fans were running at start up and didn't turn off. As I was doing the block test, I noticed the engine started revving funny, shortly after engine started to steam and then died. I checked the gauge and it read 215, I also noticed the analog display didn't work. The coolant in the reservoir wasn't boiling but the coolant in the engine was. I also smelled a weird smell coming out of the ac that I haven't smelled before. The block test also didn't read positive, but then again, I didn't have much time to use it.

don hall

Block test......exhaust test in coolant?

Have you added water (forget adding coolant....just a waste) to reservoir to fill system? If not, there may be insufficient water in the block to flow to reservoir (?).

There may not be sufficient water in the block for the temp sensor to send info to the analog gage (?).

The temp sensor needs liquid, it can't read temp from steam.

Brenden Rogers

Yes, a test for exhaust in the coolant

The coolant reservoir had the recommended amount of coolant in it. I filled it yesterday.

Could there be a problem with the flow of the coolant from the reservoir to the block? Such as the coolant already in the block stays there and no new coolant enters?

don hall

The reservoir is just an extension of the radiator. What goes into the reservoir, flows directly to the radiator, unless the hose connecting the two units is plugged. There is no recommend level for coolant in the reservoir. Fill reservoir to the brim.

Some may suggest there is an air bubble blocking flow from the block to the reservoir. The LT1 is self-purging of air, that is the reason for the positioning of the reservoir at the highest level in the engine compartment.

don hall

Are you confusing the reservoir (black container located upper-most part on fire wall with a pressure cap to the over-flow bottle located in front of rt. front tire?

The over-flow bottle has suggested marks for hot & cold levels. Water added to that bottle will not flow to the radiator.
Coolant only returns to the reservoir from the over-flow bottle via a siphon when the cooling system is correctly "closed" during cool-down.

To fill the block, you must remove the t-stat, and fill through the t-stat hole.

Note how much pressure and torque you must apply to remove the rad cap. The pressure and torque can cause a hair-line crack in the brittle brass neck of the reservoir, and can cause distortion to the cap gasket.

Brenden Rogers

Yes, I got those two mixed up.

don hall

Sounds like we are gaining..... fill the block!!

Adding water to the radiator via the reservoir only fills the radiator. It does not fill the block. At present, your cooling system is a mess. There is no doubt in my mind that the head gasket has been breached, and exhaust gas is entering the cooling system. To add water to the block, you need to remove the t-stat, and add water through the t-stat hole.

IMHO, continued filling and testing is just a waste of time. Have the vette towed to a responsible mechanic for ruptured gasket confirmation, then have the head gaskets replaced.

Brenden Rogers

Aright, I'll get to that in the next couple of days and inform you with what happens. Again, thanks for all the help.

Brenden Rogers

So here is a run down of all what happened today.

I added coolant and watched it. Single large bubbles came out of it after serval minuets. I put the cap back on and watched the car. One thing I observed was the engines weird idling. It sound like it was going to die but the revved back up. It did that non stop. Also when the car started the oil psi was higher than normal but dropped to near 0 serval minuets later. The oil psi and brightness of the display fluctuated with the cars odd revs. The analog temp display also didn't work.
Here is a run down of the temps. The car held at 190 for 5 minuets. then 200 for 5 more, then 220, then 230. At 230 is when I decided to shut off the car. When the car was shut off, I noticed steam coming out of the block near the firewall.

don hall

If exhaust gas was entering the cooling system, the rise in temp would have been immediate. Pressure would increase rapidly, and there should have been a flow of water out of the reservoir, and into the over-flow bottle.

You didn't mention water flowing to the overflow bottle, and at 230, one fan should have activated.

Cooling requires air flow, and liquid flow. Block one, or both, and the vette will overheat.

I have not read the results of your test for combustion gas in the coolant.
If test is negative, the head gasket may not be your problem.

DID YOU ADD COOLANT TO THE BLOCK THROUGH THE T-STAT HOLE?

Brenden Rogers

I just saw that you added more information to your last couple of posts. For some reason I never received notification of that. No, I didn't add water through the T-Start.

One odd thing that both fans were on at start (the ac was off) they stayed on and didn't turn off.

Once the coolant was added to the reservoir the car ran the coolest it has within the time period of the when overheating problem started.

I haven't gotten to the exhaust leak test. I will most likely to that tomorrow.

At this point I'm wanting to just take it to professionals. Luckily I live near a shop that specializes in Vette restoration.

jmgtp

You're not adding much value by continuing to run it. You need to do true diagnosing or bring it to a professional. Each time you run it is likely only making things worse and I fear you might be risking further damage - as in warping or cracking the cylinder heads. I believe you mentioned 0 psi on the oil pressure gauge as well. That's another tremendous problem but should be verified with a mechanical gauge.

It seems that your cooling system has a major problem and also that the head gaskets have failed. Steam rising from the back of the engine means coolant is leaking and evaporating. Maybe the steam tube connecting the heads has failed - or possibly the heater core.

Brenden Rogers

I'm happy to say the car was fixed and back in working order. The problem or problems I should say were the following: a small puncture in the radiator, the radiator cap wasn't holding pressure, and the MAPS sensor was busted. All exhaust leak tests came back negative and the analog display temperature gauge was replaced. Also, for good measures all the tubing in the coolant system was replaced.

95C4nick

My 95 overheated bad the other day as well. It went almoat to the "redline" on the gauge. I have a blown intake manifold gasket now. Does that mean tge headgasket is blown as well? Because i dont know if there is water passing through it.

jmgtp

You may want to start a new thread, this one is 6 yrs old.

water doesn’t pass through the LT1 intake manifold.

AZSP33D

In general, get a cheap Harbor Freight coolant system testing kit, and use the hand pump and radiator cap adapter, check to see if the system holds pressure, and also check to see at what PSI your radiator cap blows off. I think that other than cleaning out the crap in front of the radiator this is the first step in troubleshooting such issues. Apologies if it was already mentioned and done, I didn't see it. For the last posts, the intake gasket leaking at the coolant passages will be the overheating issue, no way for me to know if a head gasket is needed, but if you have coolant in the oil or intake, that's a major problem, it can quickly wipe out the cam/main/rod bearings.