Oil Temperature Control Valve Thermostatic Element Failure

[Jagdpanzer]

Went out for a drive recently and after about 30 minutes took the opportunity to scroll through the digital readouts for coolant, oil, and voltage. Coolant temp and voltage were normal however, much to my surprise found the oil temp at 240 degrees F. Normally it runs within a few degrees of the coolant temperature under street driving conditions with usual summer time ambients.
Following is an account of the steps I took for investigating and correcting the high oil temperature problem:

I replaced the oil cooler with a NOS cooler when I installed the 427 engine which had been working fine so I suspected there was something not quite right with the oil temperature regulator valve assembly.
To pull the regulator valve assembly apart from the filter housing I used a good pair of right angle internal snap ring pliers. Following photos were taking using my spare engine which was easier to photograph.
Attachment 15394
Attachment 15395
The plug released after a few taps from a soft blow hammer and wooden dowel.
Attachment 1
Before starting the investigation I left engine set for a few days to allow the oil to drain back to the sump. Had very little oil to deal with when the the retainer cap popped free.
Attachment 15396
The thermostat element that provides the force for controlling the temperature regulating valve sits right behind the access plug.
Attachment 15397
The thermostat element, regulating slide valve, and return spring are easily removed.
Attachment 15398

To be continued

[Jagdpanzer]

Bench tested thermostat element on the stove with a NOS spare element and IR temperature thermometer. Here is where the problem was uncovered.
IMG_1413.JPG
IMG_1408.JPG
The NOS spare element is on the right and the failed removed element on the left.
During the reinstall make sure the return spring is properly seated on the locating boss at the rear on the control valve bore.
IMG_1419.JPG
Slide valve installed with vent hole at twelve and six o'clock.
IMG_1422.JPG
Make sure control valve slides freely with no binding or rough spots.
IMG_1435.JPG

To be continued

[Jagdpanzer]

Here is the control valve at full travel.
IMG_1436.JPG
Lubricate the O-ring and reinstall the cover plug with a shoft blow hammer and wood dowel.
IMG_1437.JPG
Reinstall snap ring and rotate gap to the bottom to prevent water from collecting and creating corrosion.
Attachment 1
IMG_1438.JPG
A good pair of snap ring pliers makes the job easier.
IMG_1440.JPG


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[A26B]

Nice catch Mr. Wasinger and a most excellent procedural article, beautifully documented with superb illustrations. I love a good LT5 Technical Paper!

[HAWAIIZR-1]

Thank you Professor Phil! Greatly appreciate your time to document and share. 🤙🏼


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[Jagdpanzer]

Thanks guys.
The thing to keep in mind thermostatic element failure can be readily detected if you happen to select oil temperature on the digital gauge read out and notice the higher temperature. If the temperature increase is high enough you could probably see it on analog gauge as well. According to my 94 Owners manual the middle mark indicates 220 degrees F and the third mark 250 degrees oil temperature.
As our cars are getting older, with many pushing 30 years now, would be a good idea to check how your oil temperature is doing next time you have your ZR-1 out for an extended drive.

[tf95ZR1]

Great write-up!
Thanks!

So did this lower the oil temp (readout)?

[Jagdpanzer]

Originally Posted by tf95ZR1

So did this lower the oil temp (readout)?

Sure did. Back to running within a few degrees above the coolant temperature which ranges 195 to 205 degrees F driving around town and 190-195 on the open highway. A little higher during hot summer months.

[jss06c6]

Great write up Phil! Thank you! I'll check my '91 to see how it's doing and add this to my check list for client cars..

Steve

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[secondchance]

Thanks for enlightening me on the subject. Actually found the part and ordered on just in case.