Ben914951

Up for the 2nd round of a blown head gasket on my 86 951. Bought the car with a blown head gasket (from overheating as evidenced by the gasket I removed and the milkshake in the coolant).

New head, new rod bearings, etc., etc. and I blow a head gasket at 3/4 on the temp gauge, idling at an intersection. The gasket looked great when removed. It apparently lost the seal between the gasket and the head and block...don't know how. It just did it again this morning.

Temp goes from 1/4 to 3/4 quickly, then the idle starts to lope, then no power and smoke out of the tailpipe.

Any ideas...I promised myself I'd see this car through, but I am running out of resources and I am afraid the PO may have overheated the car so much it warped the block. The head is a replacement and straight. The block looked straight with a straight edge, but I dunno now.

streckfu's

Any modifications such a chips, boost controller, or wastegate?

Overheating could be casued by the headgasket being blown rather the otehr way around. You need to check your AFR and find out why the gasket is going.

Ben914951

No mods. All stock. Was failing emissions (3 times) prior to this failure

jakery

that sux guy. Welcome to rennlist BTW.

The only thing i could think of is your coolant system is clogged or full of air?

amybe thats causing overheating.

Did you burp the coolant system when you refilled it?
Have you checked to make sure nothing is clogged?
Does your Waterpump spin freely?

Did you have the head checked for flatness?

Some more info would help, was the car warmed up when this happened? how many miles did you get between gaskets? how quickly did this all happen/

Jeremy Himsel

Assuming the head is dead flat, and the block/cylinders are flat and not weeping, I would look into either a mistorqued head, one of the head studs stretched, or a stud is pulling the threads out of the block.

What torque procedure did you use when you installed the new gasket?

What type of straight edge did you use?

Did you check the flatness using a feeler gauge or by eye?

PorscheMD

I would make sure there is not a hairline crack at the top of the cylinder wall. I have seen that before...

Ben914951

The car was cold when started 5-7 mins prior to this. It was just coming up to temp.

I always bleed the system under pressure. Put the car's nose high up in the air on stands, and run it with the heat on and then bleed at the bleeder screw after full warmup, until all of the air is out. Did that on this car too, but could hear the coolant gurgling in the heater core after I shut it down.

New waterpump, hoses. I don't believe it to be clogged, but could be - had never thought of that as a possibility and the head has been off 3 times. so I've inspected the water jacket.

No seepage or water outside of the engine.

First time I *thought* it was a torquing issue - used a NA procedure. This most recent time was the 951 procedure: 15 ft/lbs, 90 degress, 90 degrees.

Checked the block and head with a proper straightedge from my shop's toolbox. But only by eye, not with a feeler gauge, but only because I could see no daylight between the straightedge and the block/head surface.

tedesco

fan running, thermostat working? Quick rise in coolant temp from 1/4 to 3/4 is strange. On non of my three 944 the temp climbs noticably above 1/4. Never ever seen it above 1/2.

AlexE

.... do you have a pic of the surface of that block.

IF you feel around the edge of the cylinder you may find that it is actually not flat. For some reasons........ I have seen 3 turbos do this. The surface is actually worn? Particularly where they normally fail on number 4.

The only other thing to rule out is a cracked head.

Ben914951

Thermostat is new and the fans are kicking on when they are supposed to. I watch the temp religiously. It's imperative. This does not seem to be an overheating issue though. I have worked on cars that have climbed up into the red and have been driven shor distances without blowing the headgasket. The few (about 250) miles I have put on it, the temp has always stayed around 1/4 pretty consistently. I have a feeling that the headgasket is blowing and as it gets worse, is when the temp starts to climb as the combustion gases enter the cooling system.

I will get a pic of the block as soon as I get the head off...AGAIN. I cleaned the block surface really well with scotch brite before reassembly and the surface looked good. I made it shine (took a while) and would think I would have noticed any imperfections on the surface...I did not. Doesn't mean it's not worth a second look.

The head should be good, but everything is suspect at this point. I really appreciate the feedback guys. Thanks for the welcome.

Very frustrated with this car at this point ( 3 blown HGs, broken cam belt & 1 bent valve and a broken cam tower).

Ski

Measure the head studs and see where the top is, should be 73-74mm, like Jeremy mentioned, you may have one or two with a problem, maybe not.

Ben914951

I am revisiting this as I got the head back off this past weekend.

Very frustrated.

No signs of anything wrong. Gasket looked perfect. Took a straight edge over both the block and the head multiple times in multiple places and could not get the thinnest of feeler gauges between the SE and the surface. All the sealing surfaces look just fine. The head studs I measured were all about 74mm maybe a *tiny bit* more or less.

I spoke with another shop today about this car and they start to suspect issues related to extreme overheating - which this car may have been subjected to before I acquired it. Things like ovaled cylinders, maybe stretched studs? They were all still quite perplexed after receiving al of the info about it's issues. Compression was 120-130 on all cylinders after the second HG replacement.

This will be the 4th time I have had this head off, and I have re-torqued the head 3 times prior to this final removal. I am beginning to wonder if some of the studs may be stretching as the block warms - for whatever reason (maybe an air lock in the jacket adjacent to the stud) and is causing the gasket to lose it's seal.

Plausible? I don't know. Without some sort of diagnosis I cannot justify re-installing the head. Got a pretty good offer for the car as-is, so I may dump and move on...

Bri Bro

Might want to have the head preasure checked for cracks. What torque procedure are you using?

KuHL 951

Checking for a crack in the head sounds best at this point as you've done everything else. Someone posted a pic last week (Lart?) of a head with a crack that was caused by extreme overheating. Without a good history of the 1st failure you certainly are at a disadvantage. All those failures must be frustrating as hell.

Ben914951

The head is not the original. I replaced it with an 8-valve head (NA). The head was a good head with new valve guides. I did the valve job on it and ground and lapped the 951's valves into it. I do not suspect it is cracked - and the HG blew on cylinder 4 first, then on cylinder 1 this time 'round.

I used the torque angle procedure as indicated in the 951 spec book to torque the head.