Thermostat blown out of engine

[Chris Morse]

Greetings Gents,

12 quarts of oil dumped in 3 seconds. After dropping the engine and trans, i spotted the thermostat WITH attaching studs popped out of the block. Only the wiring harness kept it from blowing all of the way out.

In an earlier post I mentioned the massive oil leak and the humungous blue cloud behind the car. Basically, the car was fully warmed up and when i hit 6k passing a slower vehicle, the oil dumped in about 3 seconds - both inside the engine compartment and under the car, it oiled the brakes and the back 1/4 of the car.

A bit of background: My dad had replaced the cooler twice in the last 5000 miles before i inherited the car. I had noticed scary low oil pressure and high temps, so installed the carrera cooler up front and the factory thermostat. Temps were much better 180-210 max but noticed erratic oil pressure readings, bouncing between 40-60 with little rpm change, or even steady rpm. Once, i noticed pressures around 80 at 3200 rpm.

I plan on replacing the temp and pressure senders and doing a bit of routine maintenance, but i am very worried about possible sticking pressure relief plungers.

Should i replace both pressure relief plungers and springs, or can i even do this without tearing into the engine.

Is there any reason I can't Helicoil the block thermostat studs holes and reinstall them, (with a new o ring)??? When i get the thermostat out, what should i be looking for???

Anything else i should be looking into???

Tomorrow, we will start seperating the engine and trans, checking the rear main seal, clutch, adjusting the valves.......and a lot of small stuff, while it is out.

Thanks,
chris

[Bob Kontak]

There is something fundamentally wrong. Was the thermostat installed in the correct orientation? I believe you can put it in backwards.

Just look to see if the oil passages in the male (thermo) and female (cavity) parts line up.

I think if you identify the big problem - the thermo can be held in with the repair you mention.

[Grady Clay]

Chris,

Please link to the prior thread.

Best,
Grady

[Flat6pac]

The thermostat cant be put in backwards. I would not use helicoil, I would use an insert and definitely check and replace the pressure relief piston and springs.
Bruce

[Chris Morse]

This engine has about 10K miles on an $11,500. rebuild. My dad drove the very little in his last 5 years. It seems to have performed, (pressure and temps), like a lot of other 74 911s have with no front cooler and AC

Grady, tomorrow, i will try to figure out how to link two threads.

Bob, I will check the oil passage orientation - but wouldn't this type of incorrect installation show up immediately???

Flat6pack, tell me abit more about shich insert.

Is there any propensity for the relief plunger to stick in the 911???

Are there any modified/improved plungers/springs available; e.g. longer plungers that are not as likely to cock in the bore or longer, so as to avoid divots inthe plunger bore???

seriously ignorant on the 911 oiling system and its foibles,
chris

[T77911S]

wow! when i first saw this i thought maybe the bolts came lose, but i see it is still attached to the stud. i just cant imagine the oil pressure high enough to pull 2 studs, unless they where overtightened and partially stripped to begin with. but, i see that the oil cooler was replaced twice?? why? perhaps the oil P was too high all along blowing oil coolers?
thats a lot of dirt on the tranny for a 10k rebuild.
you may need to replace the clutch disk if oil got down in there.

[Bob Kontak]

Link to previous thread.

Giant blue cloud behind car-towed home-massive oil leak

[Grady Clay]

Originally Posted by Grady Clay

I am very suspicious of the two prior cooler replacements within the past year.
I would want to very carefully inspect and measure the two oil pressure systems: one regulating and one safety.
There are many different parts to these systems and it is easy to have an incorrect combination of parts.

Originally Posted by Grady Clay

I have never seen a perfect description of all the oil pressure relief/safety pistons, springs, spacers, plugs and other. BA has a good description and there are a couple of Factory bulletins but we need actual dimension measurements, spring lengths and spring rates.

These are very reliable parts.
The problems arise when incorrect combinations are used to ‘update’. I suspect this is particularly true with the ‘oil bypass mod’ that would be on a ’74 2.7.

A good subject for a through search and another thread.

Now is the time for that thread.

The thermostat O-ring is 39.2x3 mm so I’m going to assume the bore of the thermostat hole is a nominal 40 mm diameter (1.95 in^2). With 100 psi (theoretical max for the safety pressure relief) oil pressure, the force on the thermostat should be 195 pounds. I suspect it was much more.



Whatever the pressure, lets consider the damage.
Clearly the thermostat got forced out.
I suspect the engine oil cooler is damaged.
What else?

To produce this pressure, the oil pump must have done extraordinary work.
I am concerned about the oil pump drive and the pump itself.
How about the jackshaft, gears and bearings?

When you remove the two oil pressure plugs, springs, pistons, etc., be very careful to keep everything as it is when removed.
Are there any extra pieces?

Please take pictures of each set: the horizontal one is for pressure regulation, the vertical one is for overpressure safety.

Best,
Grady

[T77911S]

grady,
hot oil producing that much pressure?

there must be something else wrong too. blocked oil passage, perhaps after the crank oiling? could the pressure relief have been put in backwords? sounds like what ever is wrong may have been that way since it was built. (2 other coolers). i am surprised the seals at the cooler did not go first.

[Grady Clay]

Chris,

Can you clearly scan the $11,500 invoice so we can see what was done?
Are there other related invoices?

I’m going to speculate that someone put something inside the pressure regulating spring and the safety spring in an attempt to raise the oil pressure.
Very bad idea.

The other (more innocent) possibility is the incorrect mix of parts in these two systems.

Of course it could be something other.
Who would have ever thought it possible for the thermostat to pull the two M6 studs?

Best,
Grady

[boyt911sc]

Originally Posted by Flat6pac

The thermostat cant be put in backwards. I would not use helicoil, I would use an insert and definitely check and replace the pressure relief piston and springs.
Bruce

Bruce,

The engine thermostats for most of the 911 engines that I've seen were designed/built to go one-way or at a specific orientation to prevent error in re-installation. I have very limited exposures in engine rebuilding and would like to know this information. What particular engines/motors are these? Thanks.

Tony

[aston@ultrasw.c]

The mounting holes in the cover are not exactly opposite each other.

In the correct orientation the tstat will slide over the studs.

Try to put it in backwards and the holes will hit the studs.

[dtw]

OK I'll say it - who built the motor?

[Por_sha911]

Originally Posted by dtw

OK I'll say it - who built the motor?

Are you thinking MM?

[Walt Fricke]

I gather this is a '74 motor? The mag case would be weaker than the later aluminum cases as far as pulling studs goes. But one never hears of the thermostat studs pulling. Amazing.

The '74 did not have the oil pressure modification which came in in '76 or so. If the springs and especially pistons from the later system (through '89) were installed, difficulties could ensue, though I don't know if they would cause this massive of a pressure overboost. I think it may be the other way around.

Post that invoice. If you got Grady on this discussion, do what he asks.

Walt

[Chris Morse]

While my wife is scanning several invoices, i can mention that the engine has been overhauled twice and fairly meticulously maintained by my dad during the 36 years of his onwership. The maintenance file is staggering.
Over the years i can see that he has addressed the oil leaks on a fairly constant basis. The thermostat has had its "O" ring replaced at least 4 or 5 times, turbo valve covers, front and rear seals, numerous oil hoses and gaskets.
One possible scenario is that sometime during its early history, there was a problem with the oil pressure relief system, hence the three colers.
Further, during at least one of the thermostat o ring replacements, someone striped or partially striped the block threads for the thermostat studs.

We haven't pressure tested the cooler yet, we are still getting stuff pulled off fo the engine so we can clean it and the trans. My initial impression is that the cooler is ok this time.

I will photo the plungers and springs as they are removed, so we can try to see if this has been screwed up.

In the few times i drove the car before my dad's passing, i was always concerned by the 20-30 psi cruising oil pressure and the 230-250+ temps in Santa Barbara.

On the drive home (600 miles), i noted the 30 psi cruise pressure and230 temps, as well as occasional 40-60psi readings at similar speeds and temps.

After the Carrera cooler installation, pressures were up but a bit erratic and temps were 180-210 and the car seemed t be doing fine.

Is this problem, "blowing out the thermostat" at all common???

Is there anything better than stock replacements available from our fine sponsor??? At the least, i want to install all new springs and plungers. Are these all accessible externally?

Wife is still working on the scans, more soon,
Thanks,
chris

[James Brown]

If you reef down on the nut (fine thread) you can pull the stud threads (coarse thread) out . Not enough to see or feel the tear out but the damage is done none the less. (non-insert stud). I suggest you check with the mechanic who did this and show him the stud. The threads most likely are full of aluminum. But my bet is he will deny it.

[Grady Clay]

Originally Posted by Chris Morse

Further, during at least one of the thermostat o ring replacements, someone striped or partially striped the block threads for the thermostat studs.

This may be the cause of the ‘blown thermostat’ and not severe overpressure.

Since this occurred at high rpm, the pressure must have been at least 60 psi and the force on the (already stripped?) thermostat studs was more than 120 pounds. Pop.

It will be important to see if the engine oil cooler leaks or shows signs of overpressure.

Originally Posted by Chris Morse

In the few times i drove the car before my dad's passing, i was always concerned by the 20-30 psi cruising oil pressure and the 230-250+ temps in Santa Barbara.

On the drive home (600 miles), i noted the 30 psi cruise pressure and230 temps, as well as occasional 40-60psi readings at similar speeds and temps.

After the Carrera cooler installation, pressures were up but a bit erratic and temps were 180-210 and the car seemed t be doing fine.

Cruising at 20-30 psi at 230-250F+ is unfortunately all to common without a front cooler and the 1.82:1 engine fan. It is good that the temps are now under control at 180-210F.

The pressure changing from the 20-30 psi range to the 40-60 psi range occasionally under similar speeds and temps is unusual.
This may be a clue.


With a thick service file, scanning and posting is a Herculean effort.
We will be able to get a good overview of the situation.
I hope there is a clue to solving this problem hiding in all those invoices.
It may be some insignificant-appearing note or part.



Something to consider:
It may turn out that there is no definitive cause from invoices and external ‘testing’.
It might be wise (necessary?) to start from scratch and rebuild the engine DIY and ‘right’.
In the interim, perhaps a good-used 3.0/3.2 might be in the mix.

I realize the car (and engine) has important family meaning.
I’m not suggesting permanently replacing the 2.7.
A well-built 2.7 can be a fun and long-lived engine.

Best,
Grady

[T77911S]

no, it is not common. and as i said, partially stripped threads and something causeing hi oil P, it was eventually going to go. perhaps thick oil with even higher pressure at cold startup weakened it even more.
i would still be concerned that something else may be blocked causeing hi pressure.
i would replace the sending unit, and maybe even put a mechanical pressure gauge on just to verify the oil pressure. also verify that the gauge will show max deflection with the sending unit dissconnected. now that i think about it more, if the gauge is showing correct oil P, then that may confirm a blockage in an oil passage, but it still does not explain why the pressure relief or safety relief did not open.

any problems with worn cams?

[euro911sc]

What would the pressure gage show if the t-stat were moving up in the bore over time? Would you not get a lot of variation in the oil pressure readings? It sounds like this was not a big pop until the end and that the t-stat may have been moving slowly up the bore until the o-ring got to a point it no longer could grip at 6000 rpm and there goes your oil out the big hole.

It may be as simple as that.

-Michael