Michael Benno

The factory external oil cooler on my 1992 MY is leaking in standard places. The rubber oil lines are also saturated with oil I am not sure if that is from the blow-off from the cooler or if the lines need replacing as well. I am fairly familiar with the leaking external cooler from previous threads (oil cooler leak, Leaking '90 S4 oil cooler, Discovered the oil leak). But I could use some additional thoughts on the repair/replacement options.

• DYI repair - JB weld or Low temp Alum weld rod (low-temp alum weld) how have these DYI repairs held up?
• Professional repair from a radiator shop - what have folks' experiences and $$ been?
• New OEM replacement - New ones go for ~$580 and are made in a different country but don't seem to be different other than being painted black. Has anyone had an issue with the later black one? I know my 1992 had a replacement silver cooler in 2015, and it leaked. So I am wondering if a new replacement would be any better.
• Aftermarket replacement external cooler - what have people used? I know 928MS has one, and Sterling did one, too. I am curious if there is one that fits pretty well.

Should I use the radiator's internal oil cooler?
I am going to replace the aging oil lines. It's time to consider the option of using both the external oil cooler and the radiator end-tank cooler to help avoid the heat soak that can occur with only the external cooler when driving in stop-and-go traffic on hot days. This has been touted as a way to mitigate heat soak issues. However, I have some concerns on this approach based on recent insights:

Radiator Endtank Cooler Leaks
There have been quite a few incidents of the coolers in the end tanks leaking (Why is There Oil in My Coolant?, 1987 928 leaking oil into coolant, Oil in Coolant , Failed Oil Cooler - Oil in Antifreeze Mess) It seems as though the frequency of occurrence is increasing to the point that some mechanics are recommending not using the internal coolers at all for risk over mixing coolant and oil (motor or trans). It would seem a risky proposition to do put the oil cooler circuit into the OEM radiator. It is certainly something I am worried about. Thoughts?

Adding more heat into the radiator
Adding the oil circuit into the radiator will definitively have an effect on the average temps in the radiator. I saw this when I was running the GTS 5spd transmission cooler line through the internal cooler and the external cooler. I found that radiator temps went up with the two coolers running in series. When I removed the end tank cooler and only used the external cooler, radiator temps went down (measured with laser temp gauge). I am wondering if adding more heat to the radiator is something that should be avoided. It would seem Porsche had a reason to remove the oil heat from the radiator in 1990, albeit their alternative was shortsighted; maybe it was to address coolant heat soak (maybe not). Thoughts on this?

Here is a picture of the cooler inside the radiator end tank for reference.


Thanks in advance for your time and consideration of this topic.

Mike

voskian

Mike I triedJB Weld to stop the leak…no go. Bought new oil cooler from Porsche. Also replace the rubber stand offs which help isolate the cooler from vibrations. My old rubber stand offs were flat!

buccicone

Michael,
Same here. When I had my '90GT I took it to a radiator shop which epoxied and did not work. Bought a new one from Porsche $$$. What Bob said about the rubber isolators.

Michael Benno

Yep, the cooler is leaking from the end tank. These leaks are a result of running the cold engine for about 10 minutes.


This was the residue on the belly pan after 30 miles of driving. This makes me think some of my GTS oil consumption issues were a result of the leaks from the cooler.


Looks like this weekend of nice weather will be spent doing the dissassembly

Tom. M

Have you thought about adding an aftermarket oil cooler (with fan)?
I think the run through the radiator in addition to the external cooler would help with preserving the cams if you were to run GT cams. Greg had posted about 90 and 91 GTs having spalling on the cams due to sitting in traffic with no air flow through the oil cooler, loss of oil pressure etc.. 89 GTs apparently didn't suffer this as badly as it only has the radiator end tank cooler (no external).
If you are planning on adding more aggressive cams to your GTS, then maybe the dual solution is the safer way to go?
I don't know how many cars have suffered from the oil cooler breaching, but have heard of lots of AT coolers breaching.

Alan

I'm not sure the late oil cooler is that effective - except at speed - overall a poor solution. In Phoenix it's a total disaster - idling in summer traffic after a high speed run the oil temp just climbs and climbs, pressure drops & drops (I think the flow rate is still probably fine - but who wants the "Christmas Tree"). I added the side tank cooler back in series (after the air/oil*) and improved the airflow through the radiator (better fans & shroud) - it really helps. Better oil helps too: find a good high temp 20W50 - I use Amsoil ZROD, there are others I have and would also use (Motul, Royal Purple etc).

* After gives the advantage of never overcooling the oil (though not such a big issue for me here...).

NB Better oil seems to have 3 effects, it is stable to a higher temperature without breaking down (loses less lubricating performance) and so lasts longer, stays more viscous at temp maintaining oil pressure better, and in my experience it actually marginally lowers worst case oil temps. I was rather surprised by the latter (though not a huge effect) - so either the coefficient of heat transfer is better - giving more effective cooler performance or it froths less in the crankcase - so picks up less additional blowby heat. Tell me what other possibilities you can imagine?

Alan

olmann

I had mine leak on my 91 GT. Tried repairing like others with no success. Bought a new one from Porsche just to have it leak a year later. No luck repairing that one either. I ended up installing an aftermarket cooler and put it in series with the cooler n my CSF radiator. It made a huge difference for me. Plus the cooler was cheaper.
I made a basic bracket utilizing the factory mounts for the cooler and spoiler. The overall dimensions ended up being the same so everything fit well.

I will see if I can find additional pictures.

Petza914

Driven DT50 15w50 is good to 300 F and what I run in both my 928s,, my 914, and a 944 S2 Has high Zinc & Phosphorous and Moly as a friction reducer. Every car I've bought and switched to driven has given a better UOA report than what the previous owner was using, including Valvoline VR1 in the 944 and Shell Rotella on both my 928s

Here's a UOA report from my 84 Euro S you guys can compare to yours for what you're using

84 Euro S - DT50 vs Shell Rotella


89 944 S2 - DT50 vs Valvoline VR1

Michael Benno

Hi Tom, Thanks for your thoughts and feedback. I don't plan to upgrade the cams in the GTS. But I am definitively worried about preventing the conditions that cause the spalling.

Aftermarket Options
I have looked into some aftermarket options for external coolers. There are not too many. Setrab makes an oil cooler that just bearly fits (~$500). 928MS and Serling have both experimented with this unit. 928MS didn't get beyond the prototype phase. Serling's version uses extra fans and looks very promising. I exchanged messages with him and he said the cooler is a very tight fit to the belly pan. He has not been able to test this yet

cooler for the BMW M3 that looks like it may fit. No information on dimensions and it uses model-specific fittings that makes plumbing problematic


These are dual-pass (deeper) coolers than the Porsche cooler, which is a single-pass. The dual pass version do have more surface area but also more depth for air to pass through. So there can be more heat soak without properly forced airflow. We would need some test data to prove these dual pass versions are actually more effective in the 928 location.

The option Brian posted looks interesting; I wonder where he sourced it and how he addressed the return line. Hopefully, he will post some

Using an external cooler with a fan is a good idea. I am not sure how to package the unit. I could put it in front of the condenser, but I am not sure how to plumb the lines around the radiator. If others have done something here, please post some details on your execution.

I am leaning towards using the two-cooler solution (external plus in-radiator) since they seem to address the heat soak issues any passive external cooler would have. I am also leaning towards replacing the radiator with a CSF with the assumption that the internal cooler is better than the owe versions.

Kevin in Atlanta

I know somebody that replaced the OEM with one of those versions up above and added three fans in a custom shroud for the three fans. I wish he'd jump in and offer up how he did that. I've seen the work it is stunning.

I'd post pictures but I don't have his permission.

Michael Benno

Yea i have seen this as well. Very beautiful and looks and effective

Kevin in Atlanta

Yeah I've seen all his custom work he's done on his stroker and his ITBs and even my engine builder goes on and on about him. Top notch.

olmann

I used the Setrab SLM592-06. For the return line on the right side of the cooler I used a 180° connector and ran the line along the top of the cooler and back to the motor. I'm not sure why I don't have better photos of the setup but these couple give you an idea.

Alan

If my stock cooler failed - I'd absolutely dump it and find a way to have a fan assisted oil cooler in addition to the radiator side tank. The stock late model oil cooler solution is just mind-bendingly stupid in my opinion for any place that sees regular 100+F days.

Alan

Michael Benno

Thanks so much, Brian! You are the best :-)

Based on all the input, I am fairly well committed to the dual cooler approach (internal + external).