drnick

GregBBRD

Try to keep in mind that my business is fixing 928s, not selling pieces.

Truthfully, it is actually counter productive for me to improve the factory oil cooling.

However, the problem is very bad....and Porsche doesn't have either a complete set of GT or GTS cams, in inventory. And even if they did have them, the price for the cams alone, is north of 4K. (Plus a set of new lifters.) Good used cams for these models are almost impossible to find....they all suffer from the same problem...worn cam lobes...from excessive oil temperatures.

Any oil cooler that improves the oil temperature is a great thing. How that happens when there is no air flowing through the cooler, when the car is sitting still in traffic, is beyond me.

That is the real problem in the 928 model....that's my point.

SwayBar

I have a set of used GTS cams in perfect condition that I don't plan on using.

GregBBRD

If perfect condition means no pits on the lobes, I'm interested! If you have the matching lifters that are marked what lobe they came off of...that's even better.

FredR

Gents,

I see some interesting inputs overnight. Apologies that numb-nuts here does not understand how to use the multi quote feature- I have tried and failed miserably! If this is explained anywhere much appreciate a link to it.

The very reason that I started this thread is based on my perception that the car struggles to control oil temperature in certain conditions. As someone who has a lot of professional knowledge/experience of control and automation in the oil industry one knows that if one sees a drop in oil pressure it is invariably going to be caused by a lowered oil viscosity or worse, reduced flow resistance due to wear of the various components. Assuming we are trying to deal with the former my historical approach has been two pronged in that I avoid rush hour traffic and I use a tub of STP in my 20W50 Shell Helix Super oil to [hopefully] boost the ZDDP content a little and also give a bit more protection as and when the oil gets really hot. As and when I have had the cam covers off I have seen no signs of pitting on the cams currently in the engine or in the S4 inlet cams I removed from the motor some 13 years ago. Similarly the original GTS cams showed no signs of wear at 70k miles [I currently run the GTS inlet and the S4 exhaust combo].

As already articulated, no car likes to sit in traffic on a hot day but some suffer more than others and I feel that the 928 [and most low slung high performance cars] suffer most in this regard. I think the ideal solution would be an oil cooler with a fan and temperature controlled actuation to cover the "stuck in traffic" scenario. A few years ago I tried to initiate a project with this in mind and purchased a very neat cooler with integral Spal fan assembly and a SPAL fan controller with intent to plumb it using AN connectors/adapters. My intent was to mount the new cooler in the wheel arch but just never got round to implementation albeit I am thinking about having a go. Maybe the system could tolerate an oil cooler in front of the a/c condenser but those things struggle as they are so reluctant to do that.

That Greg equates idle oil pressure to oil temperature is both interesting and perfectly correct. An oil temperature of 270F [ in real world units 132C] is at the limit of what mineral oils can handle. Thus if one has regular exposure to such temps then oil changes at reduced intervals are the order of the day, perhaps as little as 3000 miles [a common number used over here] due to the reduction in service half life. Synthetics should fare much better and thus justify their initial cost.

I think Carl's oil cooler initiative looks like an interesting addition to the options stable but whether it will help resolve the basic problem I raised in this thread remains to be seen. Those who follow F1 will know that these cooling systems rely entirely on air blast and F1 cars can handle being static for about 1 minute[ and then they overheat rapidly so airflow or more specifically the lack of it] is a major problem- pretty much the same kind of thing when stuck in traffic. The traffic issue is a very common problem in mega urban areas like Los Angeles and if I were living there I would be using a 20W50 synthetic- my favourite oil is Redline 20W50 that I used to use but can no longer get hold of over here [that or Kibbort Amsoil ].

Carl Fausett

Thanks, Fred. My "initiative" as it were, was to make the external oil cooler available when they weren't any more. That was my primary goal. The secondary goal was a while-you-are-at-it, could we make it better. The science is solid, and the new two-pass cooler will remove more heat than the old one. How much is what remains to be seen.

Nobody has spoken to the disadvantage of an oil cooler in the radiator - so I will. The temperature delta is much less.
The Temperature Delta: when cooling 270 degree oil with 180 degree water, the temperature difference is only 90 degrees. When the oil cooler is in the air, even at 100 degrees (all temps in F) the difference between the two temps is now 170 degrees. The temperature delta between the two mediums is much greater, and much more heat transfer will occur. This is likely why Porsche themselves moved the oil cooler out of the radiator and into the air, IMO.

As to the idea of passing the oil through two coolers, I offer this example from real life. On my race car, when making more HP I knew I would be making more heat. That's a given. So, I installed two matching large oil coolers in series to do the job. What we found though was our results did not match our expectations. It never worked as well as I had thought it should, and I came to a theory that the added restriction to flow both from the cores and the hoses actually reduced the amount of oil going through the coolers. Remember that on most engines (including the 928) oil flow to the oil coolers is passive - it doesn't have to go that way. Some oil does and a lot of oil does not. That is a good thing for a street-driven car, because if the oil cooler line should become crimped or dented while in use, you still want the engines lubrication to continue anyway. That's why they are passive-flow. Anyway - so I removed one of the two large oil coolers and of course a bunch of lines and hoses came out too. And my oil temps went down. This confirmed what I suspected - that by running two coolers in series I'd actually created more back-pressure and less oil was going through the coolers. Now using one big oil cooler, oil flow was greater, and engine temps went down.

Food for thought.

Carl Fausett

Here is a pic of that oil cooler setup from 2010. The oil coolers were in clean air, with ducting to them from the high pressure area at the nose of the car. Didn't work. Too many restrictions to the oil flow, we found. Removed one of these two oil coolers and all that extra hose and oil temps went down.

Thom

Probably because they did not want the cooled down oil that reaches the end of the core after the cooling pass to be warmed up again while flowing back in the other direction during the return pass.
As oil flows back to the LHS through the tube it won't be warmed up by warmer oil flowing down the core through the inlet. Adding a tube on the radiator core was probably retained over managing an additional x" long oil hose going across the engine bay below the fans, and even if warm air flowing out of the core may warm the return tube, oil should flow fast enough not to be significantly affected.
A twin pass core may offer improved cooling if it was thicker, as I do not think there is enough free height for a taller twin pass core.

The 944S2 and 968 oil cooler cores are physically identical except the 944S2 oil cooler is a twin pass while the 968's is single pass. This suggests to me that a single pass cooler performs better than a twin pass cooler for the same core volume.

PS : Greg, I sent you a pm regarding another topic. Thanks in advance for your attention.

Carl Fausett

You are correct, we couldn't make the oil cooler any taller without moving it closer to the pavement. That was a "no". Making it deeper was the only option available to us. The first pass is at the back of our oil cooler, then it makes the turn on the other end and comes back down the front of the oil cooler. In this way, it gets some temperature differential on both passes, and cooling will occur. Not as effective as making it taller in clean air - true - but this is all the space envelope would allow us to do.

SeanR

Great discussion guys.

I've been of the opinion, and I may be wrong, that for every day driving cars in our area which has high traffic congestion and heat, that the external oil cooler is not sufficient and it's smarter to just change the hoses and use the radiator cooler on the later cooler like all the early cars. Since the Porsche cooler is back in stock I've not had the need to convert any yet, but it's always been in the back of my mind to do so. I have installed several of Gregs hoses so it's a double cooler though and we did notice a slight bit better oil cooling like Roger stated.

ROG100

I am not saying that it is better but that it DOES add additional heat extraction in a scenario where no heat is being dissipated at all with the under rad oil cooler. As GB confirms it does cool the oil when the air to oil cooler does not. Certainly an improvement. My car is a street car as is Fred's.

As for passive flow. Ask anyone who has forgotten to reattach the oil hoses when they removed the radiator and started the car. 8 quarts of oil appears in the floor in less than 30 secs. So that tells me oil flow is good but I have never measured it beyond my mistake.

So question for the experts - how much of the oil in the engine flows through the coolers? And at what rate?

Carl - I think any product innovation for our cars is excellent and in no way am I dissing your cooler - just thinking of my own situation with a street car. The cooler for a track car or extra high performance car is well received.

ROG100

Carl - What about moving the oil cooler to the front of the radiator at the bottom? At least that way it would see air flow from the fans when stationary? What negative effect would that have on engine cooling?
The Power steering relies on a single pass line in front of the rad for cooling.
On my Mercedes AMG V12 bi-turbo there are enough coolers of various types in front of the actual radiator to sink a battleship. Oil coolers, inter-coolers & big ***** coolers. Would this work on a 928?

Thom

Whilst transferring the heat of faster-warming coolant to oil during the warm up phase will help against general engine wear while it is "cold", it does not make sense to me to hold back the radiator's ability to cool down the cylinders to the best it could if warmer oil flows through it once oil has reached its normal operating temperature, which should be higher than the 85°C/185°F the cooling system is designed to work at.
In a set up using both the radiator and the external oil cooler I would ideally try to modify the circuit so that oil does not flow anymore through the radiator once it is up to temperature. I doubt anyone driving in bump start traffic at minimal loads may see oil temperature climbing any higher than say 110°C/230°F even in very hot climate, and at the corresponding engine speeds close to idle I strongly doubt that such an oil temperature may cause any damage to the various engine bearings.

Kevin in Atlanta

Edit: I have to type faster.

Why can't the 90+ oil cooler be mounted in front of the AC condenser? Gets the benefit of the dual fans.

Wasn't the an ATF cooler mounted there on earlier models?

ROG100

In my scenario the additional heat dissipation brought about by the radiator end tank cooler is the difference of 7 psi to 15 psi (0.5 to 1.0 bar) in oil pressure. When at idle in GTS cars that is the difference between the red oil pressure light coming on or not.