wallyman424

Also have you reached out to beck?

ed devinney

Lovely car! I saw an original as a kid (in a strip mall parking lot of all places) and have been smitten ever since.

The oil cooler fan in the 993 comes on low at 212F, high at 239F - maybe you're doing ok?

wallyman424

I agree, have you ever seen above 230? What happens when you're running on an 80-90 degree day?

burgermeister

When it's above 80 ambient, I soon get to 240F oil temp, at which point I either short shift and cruise for a few laps, or I pull off and let it cool down. So I don't know where it will stabilize.

Beck's position is that there isn't a problem, whatever I am experiencing is specific to my car. Most folks who acquire one of these prefer the car show scene to the track scene, so there is little comparison to be had with other owners. I tangentially know of one other guy tracking his, but he has a 3.2 in it (higher airflow fan!).

Randy Beck does race one of their cars, and the internet is full of pictures of it. I have also seen it in person. The front inlet and ducting to the front wheel wells is very similar to my car, oil cooler is about the same size. They tend not to use stock 993 motors - which means, again, they have higher airflow fans. Thus, the original question! He does have flared rear fenders, and probably there are differences in the wheel houses both front & rear. Aerodynamics is funny, things can have very weird side effects, but I lack the resources to figure any of that out, so it is a pointless speculation.

Randy does not run an oil thermostat. As I street drive the car as well, I installed an aftermarket one similar to a MoCal (Improved Racing FSM-205). Before that, on a 50-60 deg day the oil would not get above 130F driving on the street. I have a hard time believing the thermostat could cause the issue - I have had both a Mocal (did a poor job keeping the oil warm on a cool day with street driving) and the Improved Racing thermostats in the car, and on track it ran hot with both of them. Both work by leaving the oil cooler passages open, and opening an additional passage to "short circuit" the cooler below 180F. Above that the "short circuit" passage closes, and everything has to go through the cooler. I have never tracked the car without a thermostat.

I have not checked oil cooler inlet & outlet oil temps. Not sure how I'd go about it! Any suggestions? Airflow through the cooler might be interesting, but I have no clue how to do that while driving. Air temperatures would be doable with a couple of thermocouples, but without air flow it would be totally useless. With air flow it would be partially useless, as I have nothing to compare it to ...

ed devinney

Thermocouples clamped to the pipes might not be completely accurate but should give a close number for temperature drop.

Maybe go back to the future and add a 904 GTS rear cooler?

burgermeister

The 904 has funny aero that does different things than what I'd expect. For instance, the cooling grille (904/4 location) on my Beck had air coming out of it at speed, not going into it (I tufted the area and watched in the rearview mirror). I modified it so that no longer happens, as it was coming out the grille, headed forward to the rear window, and then went back into the cooling fan inlet! The 904/6 did the same thing - they closed it off alltogether, and moved the cooling fan intake opening in the clamshell to just in front of the rear window.
Back by the transmission there is already a trans cooler, I still need to check if it is getting usably cool air or, for that matter, airflow.... I'll try the clamped thermocouple method there, and up front, next time I am on track, assuming I can order sufficiently long thermocouples still (guessing that's all chinese made stuff for what I can afford...). Or, maybe I'll take apart one of those cheapo remote BBQ temp sensors - probably easier than running wires around the car anyway.

What ought the temperature differential be, inlet to outlet, for the oil cooler?

wallyman424

I can't comment on specific inlet and outlet temperatures, but if you are able to gather enough data and graph it it may lead to a trend that helps determine where the problem truly lies.

Is the front oil cooler a dual row?

​and is there a tray under the engine?

ed devinney

I have suspicions about this ducting. It's hard to tell for sure, but the duct outlets appear the be about 7 oil cooler rows high, or about the same height as the inlet. The inlet is about as wide as the cooler, say 20 inches. That means that each outlet would need to be about 10-11 wide to flow roughly as much air as the inlet till take in. The ductwork appears to reduce to a square more or less where the pop rivets are, making it grossly undersized.

And that is just to flow the same volume of air from front to back. The air on the back side of the cooler could easily be twice as hot as the ambient air coming in, and thus either a much larger volume, or since it's contained in the ducting, a much higher pressure. Either way, the cooler is probably not getting enough cool air flowing across it to be effective. Your honor, I rest my case.

burgermeister

The 2 duct outlets combined have the same area as the front opening. The front opening is considerably less area than the oil cooler, but the body only has so much room.
The air volume change would be relative to absolute zero, so not as big as one might expect at first glance. Maybe 20% if the cooler is working well.

Regardless, if the fan can't be sped up, and I don't have room for another cooler, I need to see what the airflow situation for the current cooler is - so I will try to do that.

nothingbutgt3

Is the driver side cooler the same as the one on the passenger side? If yes, how did you manage to connect them and to fill the driver sude one? It seems to be rotated 90 degrees front, isn't it?

Bill Verburg

It's the same size but has a different I/O configuration. A second stock one can be used but the plumbing is more complicated

ToSi

Cool car - 240F isn't that hot as far as oil temps go, I bet that Mustang behind you could see 50F hotter during a lapping session.

Might try a small lip spoiler or duck bill below the front inlet to the oil cooler, probably wouldn't take more than an inch to increase airflow through the cooler by a significant amount.

burgermeister

I have heard that Ford & GM do not really worry about oil temperatures below 280F. But ...
I believe (but don't know for sure) that the usual practice at Ford & GM measures oil temperatures in the sump, meaning after the oil has passed through the engine. Porsche, at least on the Mezger engines, measures oil temperature after the pressure oil pump but before it passes through the engine. So, apples to oranges. I need to measure oil temp going into the cooler (equivalent of Ford / GM oil temp) to get a meaningful comparison there.

The desired ideal temp of 220 comes, I believe, from a study Porsche did on bearing wear way back in the 70's. I saw it someplace a number of years back. Oil temp vs. bearing wear for different weight oils - though it was unclear if that was oil temp going into the bearings, or oil temp coming out of the bearings. I expect Anderson et al used that as their basis for "220 is OK, 250 is too damn hot". I imagine modern synthetic oils (I use the Joe Gibbs 15-50 FWIW ... might just be really expensive Mobil1 in a different bottle, I have no way of knowing) can tolerate considerably higher temperatures. Also, it seems bearings are about the last thing on a Mezger engine to wear out (valve guides being 1st). On the other hand, grenading an aircooled engine is insanely expensive ...

I've got a little duckbill below the cooler opening already. One of the pictures near the top shows it. Did you have something different in mind?

MarinS4

In your shoes I would focus on getting proper airflow through the existing cooler before attempting to fit a second one. Oddly enough having a smaller frontal area (to a point) is better that having one that is too large. Think in terms of which design allows air to exit back out after pressure builds in front of cooler. For example air will find it harder to escape this type of entry with narrower mouth / \ than this type of entry with wonder mouth \ /. I know it runs counter to what you would think but it’s all about creating the highest pressure buildup in front of the cooler. Next focus should be exiting air in the lowest pressure zone possible. I suspect this is the root of your problem. Lots of data out there showing high and low pressure zones of cars.

burgermeister

OK, I have done some on-road measurements of air flow and temperatures. I need to consolidate things a bit before it goes on the track.

The cheapo thermocouple amps I bought did not work if the thermocouple was grounded (such as by placing it in contact with a metal oil line), so temp sensors are thermistors. They are more accurate than thermocouples, though quite a bit slower to react. The oil temp gage read 180 during this experiment - interestingly the return line thermistor (which ought to be ballpark engine oil temp as measured by the gage) never got above 130. Something to investigate. I've dipped thermocouples into the oil tank, and the reading was pretty close to the indicated oil temp.

Air speed & temperature was measured in free air as well as inside the exit ducting using a pitot tube and differential pressure sensor. I did compensate air density for air temperature in calculating air speed. Noisy but reasonably accurate at higher speeds; below 20MPH it becomes useless as sensor dither starts to dominate.



Pitot tube air speed sensor and free air thermistor. Another setup like this is in the center of the oil cooler exit duct.

claptrap Arduino based data logger with GPS antenna

Oil temp thermistors are under the zip-tied roll bar padding

And, here are some plots.


Looks like duct air speed is about 60% of GPS speed, and more like 75% of measured air speed.

Oil temp was still thermostat regulated, so the cooler was not getting full oil flow. No way to get there except by going on track. But it does appear to cool the oil.


Not sure what to expect, but I think 60-75% of vehicle speed is pretty decent through the cooling ductwork. The cooler has to slow the air down some.
I will probably try a small tire spoiler (lip blocking airflow from underneath the body into the wheel house), and a lip on the leading edge of the wheel house opening on the fender, to see if there are cheap improvements to be had. But my hopes are not high.