Cracked oil cooler

[Grants911]

I'm having an issue with my '77 - 911s... I'm hoping someone can help. Here are the details;

- the engine was rebuilt less than 1000 miles ago
- updated oil tensioners were installed, the head studs upgraded and the case machined
- sounds like the work was done right???

- a valve adjustment was done last summer and while it was at the shop the oil cooler ruptured at the seam. The cooler part was replaced with a "Porsche" replacement.
- I drove the car all summer and stored it for the winter
- On a weekend run in cooler weather the oil cooler ruptured again, same place, along the seam
- The replacement was done at the same shop with the same result, a split seam
- The same shop did a "diagnostic" and found one of the oil pressure springs to be shorter than spec (69mm rather than 87mm?) The shop blamed the issue on this spring and replaced the spring and the cooler.
- On the 1st drive out the oil cooler split again along the seam

That's 4 oil coolers replaced in 6 months; one original and three "Porsche" replacements for those who are counting. (not all at my cost)

I've since taken the car to a different person now who has already found that the main pressure relief spring was NOT updated to 87mm as per the previous mechanic report. It was found to be 69mm and in addition the piston is scored when it really should have been replaced.

I'm at my wits end... is this just a result of a series of defective welds on the replacement oil cooler, a result of the pressure relief valve sticking because it has the wrong length spring or scored piston or an issue that's deeper than this (blockage in the oil cooling system or worse)? Any thoughts or experience with similar issues would be appreciated.

Thank-you in advance,
Grant

[fanaudical]

Couple of questions:

- Were these all NEW coolers that were installed? What brand/part number for the coolers?
- What weight of oil was run during these failures?
- Oil temp and pressure at failure?

[tirwin]

What are the odds of getting struck by lightning 4 times? 1 cooler splitting at the weld seam is bad luck. 4 is data correlation.

I have had my '83 engine out recently and I replaced the oil cooler seals. There are two openings at the top and one at the bottom of the cooler. The top two are under pressure -- the bottom one is not. Either you are the unluckiest guy in the world or the pressure is way too high. A gut check says you're right to suspect a blockage/restriction issue. My concern would be finding the root cause and making sure that no other damage was done besides the cooler.

Possible cause? I am not qualified to hazard a guess.

If this was failure of workmanship by the first shop then you've either got to believe they can make it right or deal with finger-pointing by having a second shop involved. Given this is probably maddeningly frustrating I can certainly understand wanting to get another opinion.

I believe the oil coolers are made by Behr. At least mine was and I believe it was original to the car.

[Porboynz]

What's your oil pressure gauge telling when the engine is cold? It takes my 911 about 5km before the oil is warm enough for more than about 4000rpm or the oil pressure hits 100psi+

[cmonref]

Here is Chuck Moreland's thread about exactly the same problem.

Need help. Too much oil pressure blowing up coolers

[tirwin]

Originally Posted by cmonref

Here is Chuck Moreland's thread about exactly the same problem.

Need help. Too much oil pressure blowing up coolers

That was a great link. So the summary is that the shorter spring should be used in the '77 case. But then If I understood Grant's post correctly, the shorter one was found to be in his engine, which is correct and should not have caused his problem. That is confusing.

I'm just spitballing here (to help bump this thread) but could there be an issue with the thermostat?

Grant, I hope you find an easy fix!

[john walker's workshop]

Ambient temp when this happened? Ice cold weather and too high rpms in a cold engine will pop them.

[Grants911]

Thanks everyone. I appreciate the feedback & advice. I am humbled by this community.

The thermostat is the next thing we're looking at.

To answer a few questions;
- the car was started when the ambient temperature was mild (50 degrees f)
- RPMs were not high... under 4500
- the leak developed shortly after startup
- oil; Quaker State 20W/50 (Classic) filter is also a classic black Porsche version
- pressure was normal
- temperature was in the lower operating zone
- oil level did climb very high just before bursting the one time I was driving (the other times occurred at the mehanic's shop)
- new oil coolers were installer, Behr I believe

Thank-you,
Grant

[allaircooled]

Are both springs the shorter ones like mentioned in the link posted above?

[Grants911]

Yes, it turns out that both springs are about 69mm long.

Grant

[MikeD]

Thermostat stuck open, pushing cold oil thru the cooler.

In my experience, oil bypass or not affects which plunger you use. With the correct plunger, the long spring with guide and the shallow cap give you lower but more uniform ( I.e. 60 psi hot or cold) oil pressure. The short spring with the deep cap gives higher oil pressure overall, bumping against the max when cold (like 100psi cold, 75 psi hot).

If you use the short spring with the shallow hex cap you will have too much pressure even hot. I like the hex caps but I drill them out to the "old" 12mm depth.

Ditto for the safety valve. If you use the hex cap your safety pressure will be higher than it was with the original slotted cap.

Big oil pumps will ramp up faster than small ones.

This is based on my experimentation with my 2.2, 2.7 and 3.2 engines.

[fanaudical]

If I remember correctly, the on-engine oil cooler is pressurized regardless of thermostat position.

Grant - You mentioned that oil pressure was "normal". What numerical pressure did the gauge indicate? I recommend checking the relief pistons/bores and ensure that everything slides without binding.

[Grants911]

Thank-you, sorry. I've not been good at getting back to this question.

It looks like the piston is scored, ordering a new spring/piston kit.

The pressure was always reading "normal" on the gauges...landing between the #2 & #4 on the oil pressure gauge depending on my RPMs.

I'll keep you all posted... keep your thoughts & suggestions coming.

Thank-you,
Grant

[Grants911]

Ok, here's a sad update. I'd appreciate any thoughts, advice or condolences;

The thermostat seems to be fine, replaced the oil pressure bypass Pistons with the shorter option, checked the piston bore, looked fine, welded the oil cooler and pressure tested.

Started the car... Slightly high pressure... Let it warm up... All good... Revved the engine a bit... Pressure higher than should be but settled after a moment... Revved the engine to 3500ish RPM and the pressure pegged to the max so fast that the engine could not be turned off before yet another oil cooler failure.

Any thoughts on this?

Here's the history again;
Rebuilt 2.7 engine with upgraded oil tensioners
Rebuild done well but not by an expert. Everything points to a great job... Case machined by Oli's, upgraded studs, all seals done well etc
I drove the car all last summer without issue
Took the car in to the local Porsche shop for a valve adjustment
That's when all the issues began... Coincidence?


Any help would be much appreciated. I'm desperate to get the car on the road again!

Thanks in advance,
Grant

[DRACO A5OG]

So it cracked at the same spot on the oil cooler?

it appears the cooler can't handle the pressure build up?

Valve adjust should have nothing to do with it unless they swapped your cooler?

[tirwin]

Draco,

Not the same cooler. OP has been through 4!

Grant,

Something is obviously amiss. I can't imagine what in a valve adjustment would cause this but I think it is time for a "Come to Jesus" meeting with the shop that did it.

The root cause is going to be (a) something done by the shop that did the valve adjustment, (b) something the rebuilder did or (c) unfortunate bad luck. At this point, I don't see what you can do short of some disassembly and inspection. It really sucks, and I feel your pain.

[stephers]

Hi everyone,

The car is at my shop and I am the one that had the oil cooler welded, the fellow that welded it did a very good job and tested it at 175 psi for 2 days no leaks, reinstalled with new seals. Also replaced both pistons, springs ( short ones ) and new caps. Also replaced the engine thermostat as well. Made sure that all bores were clean ( as much as you can from the exterior of the engine ) pistons move freely in the bores.

One thing, though, the pressure relief valve on the side next to the oil pump was under quite a bit of pressure when the cap was installed, much moreso than the set up at the bottom of the engine. Check the passages with a stiff wire through the bores to see if there was a blockage ( again as much as you can from the outside of the engine) Also installed a new ( red ) filter Porsche using 20/50 Castrol GTX

My guage reads 300 psi max and after I started the car ( see above for conditions ) oil pressure at idle was 140-150 cold, let it warm up for about 15 min , pressure was at 90-100 ( this worried me ) when I blipped the throttle to 300rpm, guage was pinned to 300 psi so I am sure it went even higher,. that's when the oil cooler cracked again and 5 liters of oil over the shop floor. Could not get it shut off in time.

Took the spring and pistons out again and rechecked the, still nice and smooth but that high spring pressure on the pump check valve is bothering me. I have another bare block in the shop so I checked that as something to compare to and see what I am missing, can't seems to see anything wrong( except that high spring pressure, much higher than the set up at the bottom of the engine

Toying with the idea of cutting an old spring that I have to 2/3 and trying that just to see what happens with the pressure, used some Wurth 2 part metal epoxy on the oil cooler, hopefully that holds long enough to do some more testing. waiting for the epoxy to dry overnight to give this a try and see what goes on, this is not a fix but just trying something.

I have read all the posts about high oil pressure but all others were cured with the installation of new pistons and springs.

Any more ideas, I am open to a suggestion, never seen this before( this high a pressure anyways )

I know Grant would really like to be driving his car, especially after I did a complete suspension and steering upgrade complete with new tires.

Thanks, Rick

Thanks, Rick

[stephers]

Any one with an idea

[gestalt1]

I'm looking at the oil flow chart and here are my theory's: the oil relief valves if functioning maybe have some sort of blockage at the over-pressure outlet into the crankcase? Or maybe there is a blockage at the passage from the oil cooler exit to the crankshaft mains? Or a blockage from the mains to the cam oil lines? What I'm thinking is that at low rpm the oil feeds at the main bearings are letting the oil lube the crank but once the rpm increase they can't flow enough oil so the pressure builds too high. I doubt this but this is really a strange problem.

[MikeD]

A thought... If the engine does not have the bypass mod and you use the late piston (no side holes), there is no where for the oil to go when the pressure regulating valve opens.

But it seems you also have a failure of the safety valve which is piston agnostic which is weird.