carrera cooler versus trombone.

[vash]

ok, i have a friend that doesnt post here, ( i dont know why, never asked) but he drives a 81SC. he did a ton of modifications including LSD. basically he spent alot of money. he wants to upgrade to the carrera cooler, with the fan setup. so he wanted to check some info first. basically here is the test. we were going to go for a drive together and get the cars hot. then we would use a thermoprobe to measure supply and return lines for both our cars. and see if the difference of temps would be greater for my carrera with fan setup, compared to his trombone cooler. sound like a good plan to me. so just for curiosity, after driving back from san francisco, i checked my diff in temp (delta T) and there wasnt one! maybe a few degree difference. what gives? i measured underneath the drivers door about mid distance between the tstat and cooler. my dash temp read 210 and my thermoprobe showed 180ish at both lines? am i missing something? i should at least get a drop off just because of the length in oil lines, shouldnt i? i hope his trombone cooler doesnt do better...haha that would be poetic.

cliff

[Chuck Moreland]

Several comments:

a) Logic says you should see a big temp delta across the cooler. But it doesn't really work that way.

The oil is not making one trip through the cooler, but instead is constantly circulating - losing heat energy with each pass through the cooler and gaining it with each pass through the motor. The overall oil temp is coming down due to the cooler, and that includes the temperature of the oil EXITING the engine as well. Hence the temp delta across the cooler is smaller than you might expect.

b) IR thermometers (I assume that is what you used) don't work so well on small items like oil lines. They get confused with the surrounding temps.

c) IR Thermometers are not that accurate. You're looking for maybe a 10 degree delta.

d) Do you have a fan? Was it on? The carrera cooler without fan doesn't do much when the car isn't moving.

e) 210 isn't that hot. If the oil was hotter, youd see a bigger delta.

[ischmitz]

Chuck,

have you ever measured delta T's on your cooling system. I would be interested in what temps you see on the scavenge line, the oil cooler input line, the output, and the gravity feed line. I guess the best way would be to use thermocouples isolated from ambient airflow.

Cheers,
Ingo

[Chuck Moreland]

It's been a couple years, but I did try some testing using an IR thermometer. Difficulties as above.

I then used adhesive-strip type thermometers. Though I don't have the numbers at the ready, studying the information led me to conclusion a) above.

I concluded that delta T was not very meaningful and that the dash temp guage was the best indicator of oil cooler performance. Handy too since it's a lot easier to read.

[Eric Coffey]

I believe the IR thermometers are much more accurate if used directly on the surface of the item to be measured. The further away they are held, the larger the IR "cone" becomes. For example, most pit crews that use them to record tire temps (faster and more practical than probes) will place them directly on the tire's surface.

[palle7688]

Your thermostat in rear fender well is probably not open, thats why you don't measure any delta T.
The engine mounted oil cooler is doing it's job

[kqw]

Hmmmmm. Let's see. Trombone vs. Carrera cooler + Fan, one oil cooler vs. two oil coolers, 225x50x16 vs. 185x60x15, Sealed beam vs, Litronic, 4 speed vs. 5 speed vs. 6 speed, Mechanical chain tensioners vs. Hydraulic, 6 blade fan vs. 11 blade fan, 915 tranny vs. 950, Points + condenser vs. Electronic, one mirror vs. two mirrors, etc, etc.

Boy, Porsche sure wasted a lot time and R&D on so called improvements.

On my way to church to repent for my sarcasm......

[Joe Bob]

You need to get temps OVER normal opearting temps....do a spirited run up hill, get that puppy good and hot.....pull over and measure the oil on the dipstick.....

[vash]

Originally posted by kqw
Hmmmmm. Let's see. Trombone vs. Carrera cooler + Fan, one oil cooler vs. two oil coolers, 225x50x16 vs. 185x60x15, Sealed beam vs, Litronic, 4 speed vs. 5 speed vs. 6 speed, Mechanical chain tensioners vs. Hydraulic, 6 blade fan vs. 11 blade fan, 915 tranny vs. 950, Points + condenser vs. Electronic, one mirror vs. two mirrors, etc, etc.

Boy, Porsche sure wasted a lot time and R&D on so called improvements.

On my way to church to repent for my sarcasm......

HEY! dont make me look up your past post! i dont think you can repent for sarcasm at church, church is one of the most sarcastic places anyways. plus it should be looked at as a gift.

thanks chuck! makes sense

[Randy Webb]

Besides the above, don't use an IR "termometer" for this. Small changes in surface emissivity will strongly affect the results. These are caused by the degree of "shine" on the surface in the infrared which your eye cannot see.

Epoxy (or at least tape) a small thermocouple to each line and use those. And remember -- even then you are not measuring oil temp. You are measuring the temp. of the exterior surface of the pipe, and hoping that heat loss from that surface does not predominate over the heat input differential caused by the differential in oil temp.s

Clear as mud? Well, this why we have heat transfer courses for ME's. The area is non-trivial and requires a few graduate level courses ...