Will

Hello, everyone.

Last fall, on a cool weekend at Grattan Raceway, my oil line separated from the thermostat housing and dumped oil all over the track. I posted a note about it (read about it here),, and there were many theories about why this happened.

After some sleuthing, the likely explanation is that I got strongly into the throttle before the front oil cooler circuit was open. I have an auxiliary oil cooler in the nose of my '95 993 (the large Cargraphics cooler that fits behind the front bumper), giving me a large reservoir of cold oil (more viscous on a cold morning). Even though the oil temperature in the engine was adequately warm, I was beginning to push hard before the thermostat opened to the front oil cooler. When it did open, I was probably near the redline, and the hot oil (under higher pressure at high revs) encountered the large volume of cold, sluggish oil. So the oil line pushed its way out of the thermostat block. It is only held in by a small bracket.

Here's what I've done. First, the oil line was remounted with a beefed up bracket to hold it in place. Next, I'm careful to make sure that the front oil circuit is open before getting aggressive with the throttle. As many of you know, you can tell when this happens: First, the oil temperature rises, then falls as the front oil circuit opens, then rises again to the final operating temperature. BUT. It isn't always convenient to sit and watch the temp gauge. It can take quite a while to warm up fully, and it's difficult to watch the temperature gauge on the track. So I was thinking that what I need is a way to measure the temperature in the front oil circuit, independent of the rear oil circuit.

So...

I've fashioned an easy-to-install temperature sensing system that tells me what's going on in the front oil coolers. A quick glance at the gauge tells me whether the thermostat has opened or not. It's great!

You can buy a thermocouple that terminates in a hose clamp; perfect for wrapping around an oil line fitting. I found one that comes with 10' of braided steel cable, perfect for running it to the cockpit. I also found a 9V battery-operated temperature unit. Here's how to do it. See the photos at the end of this post.

1. Buy the following from McMaster-Carr (www.mcmaster.com):

(a) #38855K82, Magnetic-back thermocouple thermometer type J ($86.95) (this is the °F version; they also make a °C version)
(b) #37045K621, Mini-plug thermocouple with surface probe type J, flat-pin connector, 1/2" to 1-1/2" hose clamp ($26.90)
(c) #3869K33, Thermocouple and RTD connector male plug, type J ($2.89)

2. Remove your passenger-side headlight. Easy - just open the trunk, rotate the lever near the side of the headlight, and pop the whole assembly out.

3. Attach the thermocouple to the inlet to the stock fender-mounted oil cooler using the hose clamp. Remove the mini-plug from the other end to make the cable easier to route the cable into the cockpit. I could remove mine without damaging it too badly, but it worked out better to put a new mini-plug on later (see item c above).

4. Pass the cable through the rubber grommet that the headlight cables travel through, into the trunk. Route and zip-tie the cable through to the cockpit using whatever access point you can find. I passed mine through a hole in the firewall that had been used in a stereo upgrade.

5. Re-install the mini-plug (or install a new one; see item c above).

6. Mount the temperature head unit where you like. I used a piece of metal to fashion a bracket that allowed me to mount it above the floor console. (See photos) I used Radio Shack super velcro to mount it - that stuff is strong. I removed the magnetic backing plate on the head unit, since it is not glued on well, nor does the magnet provide a secure enough mounting force.

Done! When driving, you'll see the new oil gauge register ambient temperature for quite a while, then suddenly begin to rise when the thermostat opens. It'll settle in to 190 °F or so thereafter. You'll always know when your system is ready for full throttle application.

For track folks: Let your car idle in the paddock for a while before going out on the track. If the front oil temperature still reads ambient when you go out, take it easy (<4000 rpm) until the gauge shows some action. Then have fun!

PHOTOS

View through headlight hole, showing the thermocouple/hose clamp attached to the inlet to the stock auxiliary oil cooler:



Closeup of same:



Head unit:



Head unit showing mounting bracket. The on/off switch is just above the mini-plug:



Let me know if you have any questions.

User 4221

Will,
Thanks for the writeup.... This is awesome.
While my car doesn't see track duty, you gave me an excellent idea for an intelligent fan controller.
My car sees street duty in Dallas where road temps get quite high.

Using a thermocouple and fabricating a simple controller, I can control the oil cooler fans to come on at a lower temp and turn off when I want them...... Automatically.

I like this idea much better than using a toggle switch.


Thanks again.

Scott

Monique

I have a suggestion. Why not submit it for a Rennlist DIY??

See "all forums" then at the bottom of the page are the various DIY forums.

Good writeup BTW. Thks

Flying Finn

Nice DIY write-up and good tip about not going grazy when thermostat opens.

I also have an auxilary oil cooler and the temperature drop when the thermostat opens is significant (quite a bit bigger than it was with just stock cooler).

I've always kept my eye on the temp and only after thermostat has opened and oil warmed up again I've gone "full". It seems there's a reason for doing so!

Thanks for the links also, I'll get one of those gauges.
Probably I'll wrap it around the auxilary cooler though but otherwise the same.

Thank you Will!

Will

Scott: Yep, the hose clamp-style thermocouple is a great find - good luck with the fan controller.

Monique: Someone beat me to it! It's now in the DIY section.

FF: My second oil cooler is hard to get to, so I put the thermocouple on the stock oil cooler. Both are downstream of the thermostat, so I figured that when I see the oil temp rising in the stock oil cooler, it's also rising in the Cargraphic. Either way, it's very nice to know what's happening up front!

Flying Finn

I know, I've seem Jim's photos of the cool install of it!

It probably makes no difference (temperaturewise) whether it's where you have it or where I'm planning to put it. I agree, interesting to know what's going on up there!

akolodesh

thanks for the write-up. Really nice work. I have a question for the technically inept (meaning me): 1) I have only my stock oil cooler at the moment, does this work in the same way for just the single cooler and 2) if I set it up for the single cooler, how difficult is it to modify it for two coolers at a later date?

Thanks

Will

Alex,

Yes, this will work for cars with only the stock oil cooler. In fact, the way I've installed it is exactly as you would need to; I've attached the thermocouple to the stock inlet on the stock oil cooler. Later, if you add a second cooler, you can keep the thermocouple in the exact place. Keep in mind that the thermocouple is held in place by a simple hose clamp, which is easy to remove and install with just a screwdriver.

So, for those with just the stock cooler who are concerned about knowing when everything in the oil system is up to temp, this is a good system. For most people, just keeping an eye on your stock oil gauge is sufficient, but if you don't want to have to pay attention to that, the second temperature gauge is nice. It either reads ambient temperature (thermostat not yet open) or some higher number (thermostat open and the car is ready to play). No guesswork.

akolodesh

Thanks Will.
Just wondering: would it be prohibitively difficult or unnecessary to have two of these units - one for each cooler working at the same time? I am thinking about the idea of having two separate thermometers to see the differences in temp between the two systems until the oil settles at the same temp all the way around. Am I just over thinking this?

Will

Alex,

Overthinking it? Welcome to the club...

I really don't think you need two separate readings for the front oil circuit. When the thermostat opens, the front oil circuit heats up amazingly fast, and should be fairly constant throughout, i.e., I'm guessing the oil is flowing at a fast enough rate that good mixing occurs and the whole system is equilibrated fairly quickly. But hey, what do I know?

It seems that all you really need to know is that the thermostat is open. After that, just let the fun begin.

Off to Waterford Hills racetrack tomorrow for a day with the Rally Sport PCA.

JasonAndreas

Instead of adding thermocouples has anyone tried pulling a signal off the CCU wiring harness? If we could use Will's display with the existing temperature sensor the installation might be a little easier.

Nice writeup Will!

Flying Finn

I'm wondering if there could be more OEM looking gauge for this? I couldn't find anything at Mcmaster.

I 'm not a big fan of digital gauges, IMO "regular" gauge would be better.

akolodesh

Good point. A nice big analog gauge might be a bit easier to read while driving.

Will

I agree; analog rocks. Unfortunately, I spend a lot of time looking for such a gauge, to no avail. I found many digital units, but none as small as this one. Is there a temperature measurement expert out there who knows of an analog gauge for a type J thermocouple? There has to be such a beast.

BTW, my day at Waterford Hills went pretty well. The gauge performed beautifully, registering a high of about 210 °F during the hottest part of the day (ambient temps were in the 80's), and corresponded with a reading of just a bit over the 8:00 hashmark on the standard oil gauge. Idling in the paddock for 10 minutes or so was sufficient under these conditions to get the thermostat open.

Novice

IMO, this setup is overkill for such purpose.
All that is need is a thermoswitch similar to those in a laundry dryer, when the sensor reaches a preset temp the circult open/close, simply put a relay to turn off a 12V LED (from Radio Shack) when it passes a preset temperature.

Single hole drill on the dash ..... my 2 cents.