Not likely, any excessive pressure would vent from the rad cap.

John5788, I don't think that high cooling system pressure would damage the water pump; however, high pressure may force coolant out the weep hole if that's the path of least resistance.

__________________
Fred Hoelzle

A leak down test confirms it. I went in order of 1-5-3-6-2-4 and 3 was the one that was leaking into the cooling system. Pressurized the cylinder at TDC with around 30psi and I heard bubbles in the coolant reservoir.

I just hope its only a headgasket and not a cracked head.

On my '90 CE, I had pretty much the same deal when I got it. Pressure would climb too fast and leakdown showed # 4 was the problem, though it ran fine. Found a line of corrosion across the fire ring that just looked like a scratch in the cylinder head. I made lemonade since I had always wanted to go through the top end of a 104.980 and see what I could get away with.

I doubt you need to worry about a crack, you're likely looking at a failed gasket or worst case a corroded head.

__________________

90 300TE 4-M
Turbo 103, T3/T04E 50 trim
T04B cover .60 AR
Stage 3 turbine .63 AR
A2W I/C, 40 LB/HR
MS2E, 60-2 Direct Coil Control
3" Exh, AEM W/B O2
Underdrive Alt. and P/S Pulleys,
Vented Rear Discs, .034 Booster.
3.07 diffs 1st Gear Start

90 300CE 104.980
Milled & ported head, 10.3:1 compression
197° intake cam w/20° advancer
Tuned CIS ECU
4° ignition advance
PCS TCM2000, built 722.6
600W networked suction fan
Sportline sway bars
V8 rear subframe, Quaife ATB 3.06 diff

Thanks for the update.

Please post a pic of the head gasket, there are those on other threads that doubt 100 PSI would uncover a combustion to coolant leak. Given you found the problem at 30 PSI that should further reinforce the value of a pressurized cylinder test over the chemical test that checks for CO.

Cautionary tale... put a head gasket on a Honda Prelude many. many years ago (when they still looked like a flattened Civic). Still leaked, turned out to be a microscopically cracked cylinder wall! Only with the head off and a strong light in the bore did it become visible. Check the cylinder walls on #3 while you are there.

OK guys, I finally had some time this weekend to start tearing down the motor and I just got the cylinder head off and snapped some pictures. Link to high res album here: https://imgur.com/a/iaQTtqm

Original problem for refresher since its been a while: Car was overheating on the highway and noticed lots of pressure in the upper radiator hose. Leak down testing confirmed there was a leak between cylinder 3 and the cooling system.

First thing I noticed when loosening the cylinder head bolts, the exhaust side bolts were all loose compared to the intake side. So I'm wondering perhaps I should have just checked the torque on the bolt heads before taking everything off.

Once the head was removed, you can see cylinder 3 is noticeably different than the others. The piston top is relatively clean, which leads me to believe there indeed was some water leaking into this cylinder and burning off the carbon deposits.

The head gasket itself looks like the older style without the metal reinforcements built in like I see on my new Victor Reinz gasket. Would the original gasket even make it out to 200k miles in condition like this? I don't see any cracks or missing chunks anywhere.

After lifting the head gasket off the block, the mating surface on the intake side was dry while the exhaust side was moist with oil and coolant. There are beads of water and oil all over the exhaust half of the block. This further suggests that the head bolts on the exhaust side were not tight enough.

What else do you guys see/think?

Oh, and as a bonus, the timing chain guide rail on the intake side of the engine is busted:

https://scontent-sjc3-1.xx.fbcdn.net/v/t31.0-8/r270/30806254_1286404234826289_3401952208188922245_o.jpg?_nc_cat=0&oh=8155c060b5db13ab376fdcac510a6753&oe=5B5C16EB

I had planned to replace this part anyway and reseal the large timing cover and crankshaft seal.

The lower torque bolts are more from the gasket compressing than the bolts unwinding.

In theory, one could retorque the bolts but this needs to be done way before the gasket fails as once it starts to leak, the leak path probably won't close up.

Just to add a conclusion to this thread:

I finished the headgasket replacement on the motor over the weekend and got everything running. I was able to drive around 100 miles through Saturday and Sunday in 80F-90F degree weather without overheating.

After reaching temps when the thermostat opens up, the upper radiator hose gets hot and after a drive it's not gathering extra pressure to the point where I can't squeeze it anymore due to over pressure.