993 thermostat failure cooks heads QUESTION

[e p slick]

993 thermostat failure cooks heads QUESTION. I am considering transitioning from my 930 to a 1995 993. I have heard about the 993 sometimes experiencing a thermostat failure that results in cooked heads and damaged valve guides. Sound familiar to anyone? My history is with early model 911s and 930s and know little or nothing about 993s other than that the OBD1 version is more user friendly.

Also wonder how to determine if the car I am looking at may have had this problem in the past. Extensive records would show repair but this car has no records going back more than a few years.

Thanks

EP Slick

[Stealth 993]

I have never known or known of this being a issue at all. This is the first time I've even been aware of it. If the thermostat did stick, you would see the oil temp going up, & hopefully stop driving the car.

The valve guides are weak, just as weak as all the other aircooled 911's. When the valves are toast, it will burn a lot of oil, & smoke. Usually this will show up as a SAI code, or check engine light.

Yea, any car that has had the heads rebuilt will have a receipt of it, since it is an expensive repair. A good shop doing the PPI will know if the valves are bad with a compression or leak down test. You can also just remove the headers & see how much gunk is up in the heads.

Where did you hear of the thermostat causing the problem?

[axl911]

I had the thermostat failed on my 964. It failed in a stuck closed position, and did not fail overnight but gradually over time. While it is failing/failed, I did not ever see or let the oil temp go into the red zone.

I replaced the unit. But several months and thousand miles later, my car started to smoke out the tailpipe and oil consumption quickly ran from 1000 miles per quart to 400 miles. Problem was due to worn exhaust valves. I did a top end rebuilt to fix the problem. After rebuild, 1 quart goes for +5000 miles.

My guess that the failure contributed/accelerated the valve guide wear. Who know, maybe I could have gone further if the stat had not failed.

[Stealth 993]

Originally Posted by Noah

Compression/leakdown test will not tell you anything about valve guide wear...only the rate of oil consumption will, unfortunately.

Isn't a leak down done to see if the valves & pistons are seating properly? When you have poor leak down & you can hear it coming out of the valves, that kind of tells you the valve gear is worn out, or you valve seats are shot, both of which will need to be fixed.

[axl911]

Noah is correct that a leakdown won't tell you anything about valve guides. It will tell you the intake/exhaust valve seal and piston ring seal, but not the valve guides.

Originally Posted by Stealth 993

Isn't a leak down done to see if the valves & pistons are seating properly? When you have poor leak down & you can hear it coming out of the valves, that kind of tells you the valve gear is worn out, or you valve seats are shot, both of which will need to be fixed.

[e p slick]

I heard it from a cat named Franz Reimann in Munich. He has an independent service business.

Leakdown displays pressure confined to combustion chamber with both valves in closed position. Leak will exist between valve face and seat as well as past piston rings. Valve guides, good or bad, have no bearing on % numbers.

Originally Posted by Stealth 993

I have never known or known of this being a issue at all. This is the first time I've even been aware of it. If the thermostat did stick, you would see the oil temp going up, & hopefully stop driving the car.

The valve guides are weak, just as weak as all the other aircooled 911's. When the valves are toast, it will burn a lot of oil, & smoke. Usually this will show up as a SAI code, or check engine light.

Yea, any car that has had the heads rebuilt will have a receipt of it, since it is an expensive repair. A good shop doing the PPI will know if the valves are bad with a compression or leak down test. You can also just remove the headers & see how much gunk is up in the heads.

Where did you hear of the thermostat causing the problem?