Deanhinton

Good Evening Corvette Geniuses!

I’m new to Corvettes and have a conundrum ya’ll may be able to help with. I’ll put the car specs at the bottom of the post. Thank you for looking at this post!

My 1995 C4 LT1 was overflowing coolant when I would take off the reservoir cap with engine running. Took it to the shop and they tested the coolant and found hydrocarbons in the coolant. They suggested it could be a bad head gasket or cracked block and I should do a head gasket replacement.

Now I have the cylinder heads off and don’t know what I’m looking for. I don’t see any obvious signs that the gasket was damaged and leaking exhaust into a coolant passage. Would it be better to get newly rebuilt heads for about $450 each or have someone rebuild and resurface my heads?

Is there a way to test the engine block integrity before I put everything back together? Or just put new heads and gaskets on (with new bolts) and see if the problem persists?

specs:
1995 corvette base
96,000 miles
It Sat for 15 years not running before replacing fuel pump, filter, injectors, plugs, wires and getting it running again.
Didn’t overheat, but only ran it 5 miles at a time so it may have if I drove it longer.

If it helps with troubleshooting, When removing the head bolts, coolant came out of the lower front and rear cylinder head bolts on the passenger side after “completely” draining the system. I don’t know if that can happen or not in a good system.

Photos are:
cylinder head gaskets front and back
Cylinder heads
Close up of a passage that is semi clogged and the corresponding passage on the other head


Cylinder head gasket Front?

Cylinder head gasket Back?

Cylinder head gasket 2 Front?

Cylinder head gasket 2 back?

Head

Clogged port

Head

Clearer port on other head

I’m sorry if this was covered elsewhere, I couldn’t find anything specific to this problem on existing threads, but I’m sure it’s out there somewhere.

Kingtal0n

To diagnose bad HG perform compression test. And leakdown testing. And coolant pressure test.

Hydrocarbons in the coolant is meaningless on an old engine with some miles. Hydrocarbons go all over the place. Its like blood leaking into joints when you workout.

Coolant overflowing into reservoir could have been a bad radiator cap. This is diagnosed with coolant pressure test. The coolant pressure test also shows you coolant inside the cylinder (on plugs, using bore scope, or by cranking and splashing it out of the cylinder onto a sheet of paper towel).

I would say if the head gasket looks fine it probably was. If the engine ran fine and all the plugs looked the same it was perfectly healthy.

I'm not saying it was good but I'm not seeing any evidence that it was bad

Additionally bad HG cars usually smoke white smoke constantly from the exhaust. That is the main complaint a constant white smoking water. Also it will show one cylinder is very steam cleaned inside the engine where it was leaking.

You are not seeing steam cleaning, or white smoke, I guess , more signs that say NOT a bad HG

Deanhinton

Thanks for the quick reply! Those all sound like great troubleshooting steps. I did forget to add some details in the initial post.

I replaced the coolant reservoir due to a bad coolant low sensor. I didn’t replace the original cap. The first reservoir blew a seam after a 5 mile drive, so I got another reservoir and new cap.
I followed the service manual fill process, and during the refill/burping process, coolant would flow out of the top of the reservoir with the cap off and engine running. The same thing happened at the shop when they tried, even after lowering the level of coolant in the reservoir (which is what led to the hydrocarbon test.)

The over flow tank did not appear to gain coolant with the cap on and engine running, which seems weird, and there were no bubbles in the spilling over coolant, just pure, fresh coolant pouring out.

The heater was acting funny, not really putting out heat at max selected temp. I only mention this because somewhere I read that maybe the heater core could be pushing coolant out? I don’t know.

If it’s not exhaust gasses pushing out the coolant from the reservoir, what else could it be? Or where else may the gasses be coming from?

Kingtal0n

What cap are you talking about. The reservoir cap or the radiator cap. The rad cap is holding pressure inside the radiator. The reservoir cap does nothing really as the res itself is vented to atm

Water coming out of a radiator is nothing special. It doesn't mean anything without testing the coolant pressure. What was the pressure when the water was coming out, there is a tester for this all mechanics should have one. If somebody says 'bad head gasket' and doesnt perform a coolant pressure test and compression test then I dont think they are a mechanic at all.

Kingtal0n

Here are signs and symptoms and testing relation ship for bad head gasket for a normal mechanical procedure of diagnosis

1. White smoking when fully warmed up
2. Water in the oil
3. Water in the cylinder
4. Steam cleaning a cylinder upon tear down visual inspection noted
5. obvious broken head gasket piece
6. engine misfire or poor behavior like a misfire constant
7. high coolant pressure during operation
8. Oil mixing into coolant
9. Bad compression on one or two cylinders
10. Leakdown test failure, cyl wont hold pressure
11. Coolant pressure leakdown into cylinders during coolant pressure test

These are the general clues and diagnostics related to a head gasket. This is where a mechanic shall focus investigation.
Do you have any of these symptoms

Deanhinton

Thank you all again for the great replies. The coolant was flowing from the reservoir cap at the highest point in the system as far as I can tell. I had already bled the coolant system with the bleeder valve prior to this.

There wasn’t really any of the other bad head gasket signs like white smoke, water in the oil or oil in the coolant. Just the hydrocarbons in the coolant and the reservoir over-flowing.

Then with the first replacement reservoir tank blew, we just assumed that the system was over-pressurizing, negating the need for a pressure test.

I can’t really blame the mechanic for any of this, as I tend to direct mechanics away from the standard troubleshooting process with my “just enough knowledge to be dangerous” mechanical skills. And he wasn’t trying to sell me an unnecessary head gasket replacement because he said if I was going to keep the car long-term, I should do the job myself to gain more confidence working on the car.

I’m still not sure what would be causing the coolant to be pushed out of the reservoir tank with the cap off, but with the cap on, didn’t push the coolant into the overflow tank.

I attached a video of the reservoir tank seam blown out after a 10 minute test drive. Mostly just for fun, but it may be important.

Nilak

I have similar symptoms: coolant would spill out when I opened the top coolant tank that has the pressure valve before it reached 185F. I didn't do a HC test but did a CO2 one instead and it came out positive, so it seems that combustion gasses got into the coolant. I also have a PH meter and measured 6.9 which so it's starting to get acidic. I've started to do the leakdown and copression tests but didn;t finish yet. No. 1 was good, the No3 has some slight leak that can be heard, I guess there are some corbon deposits.
you could also try the CO2 next time, and you could do a magmaflux test for the block, but it requires complete a teardown of the engine

Kingtal0n

All I See is a bad reservoir tank. Without knowing the pressure there is no way to say whether the system was over pressurized. Bad replacement parts do happen. The cap could be bad if it was not replaced. The seam on that thing looks highly suspect to this type of failure IMHO.

People install new parts all the time that are worse than the ones they removed it doesn't mean anything, qualitative data only is not statistically significant.

For example the fuel tanks on 95 nissan 240 all crack in the same spot. You can buy a new one from the dealer but the mold is bad and it cracks in the same spot. Doesn't mean there is something wrong with the fuel system its just a bad design.

Measure the coolant pressure. Verify the cap is working. Think about it this way, if the cap is working, there is no over-pressurization possible. It just overflows coolant to a reservoir. IF you blew the system up with REALLY too much pressure its just a bad radiator cap. You need to clearly find the reservoir and and indicate it as being different from the coolant system with the radiator cap.

Deanhinton

I have caused some confusion. I’ve never had a car where the radiator cap wasn’t directly on the radiator.

I do think the first replacement tank was a bad replacement part, but just in case I replaced the pressure “Radiator” cap on top of the radiator reservoir on the second replacement tank. I haven’t had any problems with the white, non-pressurized overflow tank or the cap.

Looking at the service manual for filling the coolant, I’m pretty sure the coolant is not supposed to pour out the top of the system while the engine is running.

If exhaust isn’t getting through at the head gasket and pushing out the coolant, are there any other places it could be getting into the coolant system? Maybe cracked head? Cracked block? Heater core? Maybe it’s not exhaust? What else could be pushing the coolant out? Maybe it just hadn’t been purged of air enough?

Whaleman

Since you have the heads off I would take them to a shop to be gone through. Dan

Kingtal0n

Your only symptom is a leaking reservoir tank possibly caused by high pressure. The pressure regulation happens at the radiator cap. This means either the rad cap is bad or the tank is bad. If the head gasket was bad putting pressure into the cooling system you would have radiator overflow but not a blown/leaking tank. Furthermore there would be white smoke, steam cleaning cylinder, cooling oil mixture, bubbles frothing from the cooling system, poor engine behavior, etc... I don't see any of these symptoms. If there is something mixing from cylinder to oil or coolant it would be apparent in some way when looking at the affected cylinder if it was bad enough to cause macroscopic symptoms.

You could have the heads checked block checked etc... but due to their age I suspect there will be problems with both even if those problem do not contribute to your issues. For example its common for heads to not be flat after years of service. This doesn't mean they are leaking its just a thing that happens over time to most engines and they still run fine, the imperfections are taken up by the gasket and similitude of warpage in the deck to match the block, plus the general setting/sticking of gasket materials over long periods of heat/cycling greatly contributes to their sealing despite warpage.

Deanhinton

Thanks for the replies! I will certainly apply as much of that great info to this problem (and use even more next time there’s an issue before taking the heads off!).

Once the project is complete I’ll also provide an update. I’m taking the opportunity to correct some other minor problems while I have everything apart and there’s room to work.