Severe overheating issue - running out of ideas

[kojo911]

Agree w gogo22 checking the pressure relief valve is fairly simple. You can at least cross it off the list. That said it sounds like the cooler is seeing oil which suggests that the pressure relief valve is functioning.

[T77911S]

i seem to remember someone putting the engine Tstat back in wrong and causing heating problems so i was trying to search for it. not a fan of searching this forum. i did not find it.
but some other ideas.
wires to the temp gauge and pressure gauge crossed.
this seems quite obvious but someone did this. no hose from the engine shroud down to the heater boxes. air blowing into engine bay.
of course as others have implied, you are not really overheating. check temps with thermo.
waaaay too lean. timing too advanced.

[Dogbreath]

Thank you for all of the excellent suggestions.

I want to answer some of the questions that have been posted:

- I had the oil cooler out when I dropped the engine. It looked clean and in fairly decent shape. I sprayed the fins with carb cleaner and they were fairly clean.

- There are no mice nests or blockages. I had the sheet metal off the fan and can see the cone on the back of the alternator and all of the cylinders. They look free of any debris.

- The internal thermostat was tested in hot oil along side another thermostat that I had. It opened up fine and appeared to be functioning properly.

- I have only the one internal oil cooler so there are no other thermostats.

- I am in Raleigh, NC.

- My infrared thermostat is brand new and appears to be working properly.

- When I take temperature readings from the oil return lines and the lines on the oil cooler they are usually very close to the reading I get on the dashboard gauge.

- I have replaced with new the oil temperature sensor and the sender.

- The oil was changed and is at the proper level.

- I have the set the timing and adjusted the valves.

- Sump plate is oriented properly.

- Fan does not turn easily by hand.

Questions I have:

One thing I have not done is pulled the Oil Pressure Release valves. I do recall reading a post where the poster said it resolved his problem, however my question is aren't the release valves there to prevent oil pressure from going too high? My oil pressure is very low.

Many of the suggestions folks have, like blocked cam spray oil lines, lean fuel mixture, are good but seem like the they wouldn't lead to the car overheating as quickly as it is. I can see the car running hot in general under these conditions. But my car is at 250 degrees and climbing within 10 minutes of starting it from cold.

Thanks again for all of the suggestions.

[kodioneill]

If your oil pressure is low one of the valves could be stuck open.

[manbridge 74]

Is it possible the wrong t-stat is in there? I recall a thread showing t-stat windows at different heights for different years.

Low oil pressure could indicate Safety Pressure relief problems in addition to Oil Pressure Relief valve?

[schumicat]

read gogo22's post, he suggested that the pressure relief valve when stuck open on his car prevented normal oil flow (I guess because a bypass opens and it bypasses something).

[uwanna]

Originally Posted by Dogbreath

One thing I have not done is pulled the Oil Pressure Release valves. I do recall reading a post where the poster said it resolved his problem, however my question is aren't the release valves there to prevent oil pressure from going too high? My oil pressure is very low.

Check this diagram, if the pressure relief valve has too little spring tension or a stuck open piston, it would allow the oil to just recycle back to the pressure pump inlet. Ergo LOW oil pressure and recycling the same oil over and over. So a defective pressure relief valve (low spring tension or stuck open piston), instead of protecting against excessive oil pressure can lead to low pressure and over heating. The poster who claimed fixing his pressure relief valve cured his over heating, may have hit it on the head!

[Bob Kontak]

Is the pressure relief valve bi-directional?

[kodioneill]

Possible silicone stuck at or in the relief valve this may be the grail!

[kach22i]

On my 1977 I once paid a hack shop to do a full tune up, problem was the distributor had to be re-indexed as it was all the way over to one side of the slot, and could not be turned/rotated anymore.

I had no low end power and it was running 30 degrees too hot on warm days.

Once I got it re-indexed (by myself and no thanks to that hack shop), I was able to get the ignition timing right. It ran cool and like a Porsche should after that.

Related thread:
Backfiring and Running Hot

Useful Thread:
77 911s running issues

Look at the Walter_Middie posts...........for re-indexing procedure if you need it.
JWalker + 35Deg + 3.5CO = HP

[uwanna]

Originally Posted by Bob Kontak

Is the pressure relief valve bi-directional?

It appears to be unidirectional.

[Bob Kontak]

Originally Posted by uwanna

It appears to be unidirectional.
]

Thanks for the diagram. Helps to understand and follow your logic. Make sense to me.

[Dogbreath]

Tonight, I decided to pull the oil pressure relief valves and take a look at them.

First, I pulled the one the runs horizontally (letter B in the diagram above).
There appeared to be a fair amount of tension on the spring and I was able to easily pull out the piston with a magnet.
The piston looked like the one on the right in the picture below. (it has holes in it)
I wiped it off and put it back in.

Next, I pulled the valve that runs vertically (letter A in the diagram above). The spring on this one also felt like it had good tension and although it was quite a bit more difficult I was able to pull the piston out with a magnet. This piston however was the same as the one on the left in in the picture below (no holes in it)

Now I am not sure which is the correct piston.

Recall, that this is a 1974 2.7 engine and I do not know for sure, but I believe it has never been opened up and would therefore not have the oil bypass modification.

So the question is...which is the correct piston for a 1974 engine without a bypass mod. PP has the piston listed in the catalog as 911-107-512-00 for 911's (1974-89) which appears to be the one pictured on the left in the picture below.

Frankly, there is no telling why these valves would have been changed in the first place but maybe it was someones attempt at correcting the overheating issue.

Should I replace the piston with holes in it with one that does not have holes?

Thanks again for all of the help.

[dtw]

If both relief pistons were deep in their bores, they're not your issue. At this point it sounds like your oil flow is fine and stuff like airflow, timing, head studs, valve guides, and AFRs should be looked at.

Shoot me a PM if you'd like some help with this in August (am busy till then).

[Bob Kontak]

Hmmmmm.

uwanna's post #51 indicates the big change out is with the SC in 78 but your pic in post #53 indicates you may be using a pre-SC system mod.

Unfortunately, there is no info if the reverse is performed - i.e., solid plunger in the pre 1976 system.

Measure the spring. Is it 70mm (2.8 inches) or 85mm (3.3 inches).

[Bob Kontak]

Originally Posted by dtw

.............At this point it sounds like your oil flow is fine and stuff like airflow, timing, head studs, valve guides, and AFRs should be looked at.

Thinking about this comment from an arm's length back...... How does the car run when it runs? It is a lower compression engine. It should idle easy, rev easy - not fast - just easy, and not sound stressed at all. It is a 140-160-ish hp car. It should be "chillin" when it runs if set up right, it can't do much more.

Where are you located? May be as simple as a fellow pelican with some experience under his belt to just listen to it. Also, a private youtube video of the engine running with the link posted here may shed some light.

[mca]

What about a broken valve spring or springs?

My old engine was running hot. I sold it to T77911S after rebuilding a spare engine. He found a broken spring.

Just a thought.

Also, I feel that headers without heat exchangers create more heat on the bottom of the engine. For example, I put SSIs on my new engine but used block off plates prior to backdating my heater. Temps were MUCH higher with this setup. Once I got air running through the exchangers I probably saw a 15 degree drop in temps.

[T77911S]

i ran across this in an up-fixin last night. it too mentioned the pressure relief.

the first thing i did was look at the oil diagram to see if that or the safety valve could cause it and i thought maybe the safety valve

[911SauCy]

Originally Posted by mca

What about a broken valve spring or springs?

My old engine was running hot. I sold it to T77911S after rebuilding a spare engine. He found a broken spring.

Just a thought.

Also, I feel that headers without heat exchangers create more heat on the bottom of the engine. For example, I put SSIs on my new engine but used block off plates prior to backdating my heater. Temps were MUCH higher with this setup. Once I got air running through the exchangers I probably saw a 15 degree drop in temps.

I was wondering if my newly added block-off plate with stock exchangers could have added to my heat situation as well.

After I get my crap fuel lines replaced tonight, I will be performing the OPRV update (78sc) in an effort to get my temps down and oil pressure on the steady.

...then the Carrera cooler

[Bob Kontak]

Originally Posted by T77911S

i seem to remember someone putting the engine Tstat back in wrong and causing heating problems so i was trying to search for it. not a fan of searching this forum. i did not find it.

I did find one thread - 3 posts long where someone said the stat has slightly off-center fastening holes that will not allow this to occur. However, on my 1981 I remember being confused as to which way the t-stat went in until I looked at the placement of the oil flow holes in the bore and the "piston" (Tstat) and was able to align them with comfort.

Soooo, I am not really sure if you can or cannot put it in backwards. One post from one dude does not lock down that it can't be done.

911SuaCy - do you remember aligning the oil passage holes up during tstat install - or do remember the two bolt holes aligning only one way? Would be nice to put the tstat issue to bed.

I am thinking since you pulled one and re-installed another, you probably took a good look at things.