edfishjr

Opinions, please!

Well-cared for 1989 944 (2.7 liter) with 130K miles, all stock engine, just put back on the road after being up for 2 years.

Car is running and I've been auto-crossing it. Yesterday a buddy helped me do compression and leak down tests.

Numbers were good.
Compression 200, 200, 205, 205.
Leakdown numbers were 4% to 9%, the worst being #2.

As I'm putting the plugs back in my buddy pulls out a borescope and we put it down #1. I see something strange: a drop of fluid, what looks like coolant, running down the cylinder wall. Piston and wall look good, BTW. My buddy thinks it might be oil, but it looks too thin to me.

When I back the car up we have a lot of coolant on the floor... maybe 6 or 8 ounces. I leave the car running for a while but no more drips out. My garage floor at home is dry as a bone, but I had some coolant overflow at one autocross.

Gotta be the 80psi leak-down air pressure forcing coolant out the over-flow through a slightly blown head gasket, right? Any other possibilities?

Van

If it's a) running well, b) no white smoke coming out the tailpipe, and c) not overheating, then you don't have a head gasket issue. If you do have one of those problems, then it's a different story.

edfishjr

Thanks for the reply. I've noticed none of those issues presently.

Cold coolant level definitely low this morning.

camelman

My 1990 S2 had no obvious issues with smoke, steam, frothy oil/coolant, or fluid consumption. The head gasket was definitely blown though, and it slowly lost power over the course of 500 miles or so. The head had deep corrosion pitting that allowed small amounts of coolant to enter the cylinders past the fire ring and clean the pistons. Cylinder #2 was also down 40% on compression at that point. The other cylinders may have been down too, but I don’t know if my gauge is very accurate (180 psi, 130, 180, 180).

I think I also ruined a catalytic converter during this process. It must have overheated enough times from poor combustion to become brittle and crack the casing. I put on a spare and promptly had it glow bright red. Waiting to see if I ruined it too.

Check your plugs to see if they’re clean. That can indicate water intrusion. A boroscope of the cylinders will reveal the same for the pistons and head.

Regards,
Camelman

edfishjr

Plugs look good, no deposits, good color, but only a few hundred miles on them. Piston has healthy carbon deposits in the middle but clean near the edges, just like I've seen in videos of before and after Seafoam. Wasn't able to see the valves.

The car was very conservatively female driven for 100K before my ownership and maintained by her ex-aircraft mechanic husband. It seems to be running better the more I flog it.

camelman

You can see what I found in the following post. The #4 and a #1 cylinders had the most obvious water intrusion, although the #2 cylinder had the lowest compression.

I can't really comment on your carbon deposits and cleanliness without knowing the history of your engine. If I was in your position, then I'd just listen for changes in the engine, and monitor for loss of power. Maybe boroscope it on a regular basis for a while. It's easy to get scared about something that might not be an issue, but it's also possible for something to creep up on you and require maintenance.

https://rennlist.com/forums/924-931-...g-944s2-2.html

Regards,
Camelman

edfishjr

That was an interesting thread! Car running good now?

camelman

It's not back together yet, so still waiting for final results. The new guides and seals arrived today, so I'll drop them off at the machinist's and hopefully have the head ready for install later this week.

edfishjr

Decarboned #1 piston

Update: The head gasket was in really bad shape. The fiber looked chewed up with places where it was very thin (or gone) and with cracks running thru it.

I finally had a good break in competition and pulled the head. On Wednesday I took it to Memphis Motorwerks to be reconditioned. Very impressive facility and people. M96's being rebuilt, air-cooled 911's, Spec Miata motors, Nissan V6's, BMW engines, etc.

New springs & guides, all valves cleaned up good. A light skim of the deck (little to no aluminum corrosion) and I'll have it back next week.

Moral of the story: don't wait until you see white smoke coming out the back, or have poor compression or leak-down. If you have over 100K on the stock fiber head-gasket start planning to replace it. In my case the only symptom was slight coolant usage. The borescope then showed coolant in the cylinders.

PS: I forgot how huge around these pistons are!

camelman

I’m glad to hear your corrosion was minimal. The rest of the repair sounds pretty standard, so I think you came out very well. I have a 1983 NA that’s being converted to a race car, and the head gasket is definitely leaking on it. I bought a spare head in good shape so I can install a steam cent kit for the back of the head to kerp from overheating around the #4 cylinder. The current head gasket issues are just from age though.

My S2 runs like a champ now! I think you’ll be happy with your repair too.

edfishjr

Glad to hear you got the S2 back together.