Markoneus

Hey all

I've got an '86 951 with 155k miles, a replaced Vitesse Stage 2 Turbo done about 5-6 yrs ago (w/ upgraded water pump @ time). Started overheating on a long hot (88-92) highway drive through North Carolina the other day. Level gradually went above the white line, but not quite to redline. Was hovering there, slightly going up, then down. I finally pulled over in a rest area to open the hood & take a look, let things cool down. This was probably stupid, maybe should have let fans run more, b/c it blew 2 hoses badly (one tore a 2 inch slash) after I shut if off, all fluid drained out. Had it towed to a shop (Foreign Accents, all Euro car work, porsche/ ferrari/ jag etc) in Greensboro. they couldn't find anything obvious, and just replaced the 2 hoses and sent me on my way, even when I said, "Well what caused it to overheat?"

Sure enough the problem came back on the 2nd drive. (first drive it was pretty much fine) But it didn't just go straight to high level/ just below redline, it was fluctuating pretty wildly. And often came down again (to 1/3 level) when I came to a stop at a light, or started accellerating again. It was only when I was steadily cruising at a casual 50-55 in 4th or 5th (very low load on engine) where it would creep up again. Finally pulled over and sure enough another hose had a smaller leak. Car lost 2 gallons of coolant. Had it towed back to shop again. they found a 2nd blown hose this time, too.

They're warning me it might be a head gasket, but as that's a big $$$ job (I don't wrench, have no garage), I'm hoping it's just a bad thermostat. Would that explain the erratic temp? It's almost like the fan/ radiator was working once in a while, cooling it down, then just shut off and everything heated up again? Other explanations? They said they only way to really tell if the thermostat is bad is to replace it and see if the problem goes away.

Open to all advice.

The gasket is prob 60k old, was a "cardboard type material sandwiched over a metal core, which the installer said should last forever" according to my dad, the previous owner.

thx.

User 52121

Typically a wildly fluctuating temp gauge, and running hot at highway speeds but around town, is indicative of air in the system.

Hoses don't just burst on their own unless they're fairly old and crusty. If I had to wager a guess, it would be that your hoses were due to be replaced. One started leaking enough to push the coolant down, car started to run hot, then when you finally shut it down it got hot enough to burst the hose the rest of the way. Then after the shop repaired it and didn't bleed it, you have a fluctuating temp gauge.

That'd be my guess anyways. Try bleeding the system.

lart951

the gasket sounds like the MLS which much stronger than any oem gasket

jg951

+1 bleed the system several times, check your coolant level everyday. Thermostats are cheap, I got lucky and that was the problem on my car, a stuck closed thermostat. You probably got air in the system. keep us posted

Markoneus

Thx guys.

I'd love to think it's not the gasket. This description from the "head gasket rebuild procedure" link is what got me worried:http://members.rennlist.com/tom86951/headgasket.htm
"When the head gasket leaks, combustion pressures escape into the water jackets. This creates air pockets in the cooling system and the same erratic cooling symptoms as a cooling system that needs to be vented (e.g., a rise in temperature at idle, with a very fast fall in temperature when you rev the motor)"

Because that pattern is EXACTLY what I witnessed while driving it. but I realize this could just be air in the system from it having not been bled properly. That'd be a relief.

Keep the opinions coming, this helps a lot...

Voith

Start a cold engine for 10 seconds and shut it off. If the pressure in cooling system builds, your gasket is leaking.

michaelmount123

You've most likely got a head gasket issue - it needs replacing. BUT....you should certainly try the simple/cheap things first. Put a new thermostat in the water pump and give it a try. You've got nothing to lose, everything to gain.

The previous gasket sounds like a standard OEM gasket. It's typical they start leaking after a while with a bigger turbo / higher boost. Unfortunately, it goes with the territory. Replace it and go for another XXK miles.

Oddjob

In addition to overheating, common HG leak symptom is for the cooling system to overpressurize (from combustion gas getting into the water jacket) and blowing coolant out the drain hose off the reservoir cap.

Start w/ changing the thermostat. Check the old one in boiling water and see if it operates correctly.

lart951

but if he has a mls gasket, by his description , those gaskets are nearly impossible to blown. I'll be looking somewhere else unless he has a stock or widefire than it's more likely.

Tom M'Guinn

Start by fixing all the known leaks, venting the system thoroughly, and then pressure testing the system. I pinhole leak can be impossible to detect by eye because the coolant just steams off when hot without leaving drips, etc. A pressure tester, like the one linked below, will confirm if you have any leaks or not.

http://www.sears.com/craftsman-cooli...1&blockType=G1

If coolant is getting out, then air is getting in, which makes your car impossible to keep vented and otherwise creates many of the same symptoms of a blown head gasket (including the symptoms you describe).

While anything is possible, I would not first suspect a bad thermostat with your car -- they tend to be good or bad, not intermittent, and a bad thermostat does not let air into the system by itself. Also feel the radiator hose to see if it is cold when the engine is warmed up -- if its hot, then thermostat is probably opening and ok.

If you rule out leaks and air pockets and thermostats (or can't get the air pockets to go away dispite no leaks and multiple venting attempts) then do the head gasket overflow test described in that write up. Good luck!

Markoneus

@ michaelmount123 :

Yeah, this is NOT an OEM gasket. It was replaced @ 90k by a 951 guy in NH named Blair Talbot (anyone here know his work?). He works mostly on tracked 951s, and this is the gasket he puts in 951s that are tweaked up to 450hp, so it should be more than fine for mine (only 290whp est).

really hoping it's just the thermostat.

One other theory: bad radiator switch? This spring I had a ton of maintenance done on the car, and one thing they (PowerTech in NJ) found was a bad radiator switch at slow speeds. (I guess there's two?) So when it was parked/ at low speeds, the fan wasn't turning on. He replaced it and it worked fine. But is it possible there's a 2nd fan switch (highway speeds?) that's now failed?

David Floyd

If it is a MLS gasket, in my experience using them over the last 7-8 years, they do not fail like a stock gasket does, but simply start leaking into the coolant system, seems to happen to me every 2-3 years (I think from cylinder walk)

I was at the track yesterday, we were all pulled into pit lane for track clean up after a spin, noticed my water temp rise to the 2nd white line.. not normal, turn the heat on temp drops and back out on the track we go, make a few laps feel the motor stumble, so I come into the pits and sure enough coolant was pressurized spewed a little out of the rad cap... so I will be changing the head gasket.

Like michaelmount123 said " It's typical they start leaking after a while with a bigger turbo / higher boost. Unfortunately, it goes with the territory. Replace it and go for another XXK miles. "

lart951

Danno's procedure to install the MLS gasket was the best, I never had issues with the mls over 4 years and the lartmobile ran 21psi daily and occasionally 23psi, so I would call it not installing the MLS properly.

David Floyd

The first MLS I used was bought from Danno and installed per his instructions using copper spray sealant... held up no longer than dry and as you know length of time on boost street/track is not the same.

As for the OP, could be installation issue.. but installed 5-6 years ago and has 60k miles on it so I say the install was good, just simply time for a new one

User 52121

+1 to everything Tom said above, in this order.