I just spent the past few days installing a Derale Oil Cooler on my 86 Vette.

Everything works fine and I can tell that the oil cooler is functioning because of the different temps I feel in the pressure/return hoses.

Problem is with the oil temp gauge on the dashboard. The gauge is pegged at 320 degrees F until I rev the engine, then it drops to 180 range, only to peg again.

I thought the sensor might be malfunctioning, so I reconnected the stock antifreeze oil cooler arrangement; then the gauge read normally.

Has anyone had a similar problem? Does the sensor, which is located above the oil filter, need to be relocated?

Any suggestions would be appreciated.

Thanks,

Jake

 

You mean no with a digital dash has installed an oil cooler?

There's gotta be someone out there.

Jake

 

That does sound odd.

Are you using the stock oil temp sender in both situations - with the new oil cooler and with the original radiator/heat exchanger?

How long do you let the engine run after you installed the new cooler? How was the oil pressure? How was the oil level? Obviously you must add some extra oil to compensate for the increased volume of the cooler and the associated lines. I wonder if the oil temp sender was just picking up and air pocket in the line when it went to 320, and then when you gave it throttle it cleared out. Also, is the cooler positioned higher than the oulet, so that the oil in the cooler drains back into the oilpan whent he engine is not running?

 

Thanks for responding, Monty.

I'll try to answer your questions:

The stock heat exchanger has to be permanently removed to allow the mounting of Derale's adapter. The adapter screws in place of the exchanger and has two 1/2" NPT hose bibs - in and out -, then the oil filter screws onto the adapter. After the heat exchanger was removed I rerouted the coolant (which normally ran through the exchanger) to maintain proper coolant flow.

I added about half a quart of add'l quart of oil after installing the cooler. I let the engine run for about 20 minutes, then shut it down for another 20 or so, the checked and topped off the oil level.

I bought a Derale thermostat which by-passes the cooler until oil temps reach 170 degrees F, then it gradually opens. The thermostat is designed to prevent drain back of the oil.

The sender unit is the original, stock one, installed in the stock location - above the oil filter housing - and was never touched during the installation.

I've let the engine run in the garage for almost an hour and have driven the car on the street for another hour or so.

Pressures in both instances remains lightly higher than those prior to the cooler installation. I attribute this to the oil actually running cooler and, so, the viscosity remains higher.

There is a definite difference in the temps of the pressure and return hoses. The pressure hose in much hotter than the return hose, but I can still keep my hand on it, so I know it's not 320 degrees F.

The temp gauge, while on the road, jumps all over the place. Jumps in 10 to 20 degree increments, up and down, up and down; yet when I switch over to pressure, the pressure is relatively steady, with only normal flucuations.

The cooler itself is mounted directly behind the front license plate location with the fan forward and setup as a pusher (had to flip the fan blades and swap + and - wiring since from Derale it's setup as a puller).

There are no other abnormal conditions and if it wasn't for the crazy activity of the digital gauge, things would be fine.

So, last night I bought a new sender and "T" fittings to allow me to reposition the sender to the return area of the cooler. I plan to "T" in where the cooled oil returns from the cooler to the engine, rather than use the stock location which is 8"/10" higher on the block.

We'll see what that does for my schizo temp gauge.

You may be right; it could be that the stock location is not continually remaining in contact with oil and causing the gauge to peg at 320.

I emailed Derale about the problem but haven't heard back yet.

Let me know if you have any other thoughts. I'll keep you posted.

Jake


[Modified by JAKE, 2:08 PM 11/2/2001]

 

Jake,
I wish I could give you some feedback on your situation, but I don't know. I do have a question for you. My oil temp gauge doesn't read right either. The analog always just says "low" and the digital doesn't move. Is there only 1 oil temp sensor the one over the oil filter?
Thanks,

 

My 86 only has one sender unit and it's located above the oil filter. I don't know about other years though. I don't have an analog gauge either.

Maybe someone that has the same year car as yours can answer your questions.

My digital gauge remains showing "Lo" until the oil temp reaches 150 degrees F, then the digital takes over and begins showing a reading.

Hope this helps.

Jake

 

PROBLEM SOLVED!

I relocated the oil temp sender to the "out" line leading TO the Derale oil cooler and now the gauge reads normally again. I thought of installing it in the "in" line (after the cooler had done it's work and the oil was returning to the engine) but I figured I'd rather see the highest temp the oil reaches. I've got to sleep on that; maybe I'll swap the sender to the other line.

I let the car idle in the driveway for over 45 minutes and then took it out on a 20 mile drive on the interstate and the oil temp remained in the low 190s. No more wild jumps in temp and the temp never even got close to 200 degrees F., much less pegging the gauge at 320.

I guess the stock location is specific for the factory coolant heat exchanger being used; not an aftermarket unit.

Happy Days Are Here Again!

Thanks Monty,

Jake