External T-Stat Bad?

[Ayles]

My SC has been running hot since I finished the build. I added an oil cooler and fan and that didn't seem to help much.

A couple weeks ago I drove in weather that might have hit over 80 and saw the temps climb to the upper white tick mark but didn't pass it and never got the feeling that fan turned on. Which leads me to believe hot oil isn't reaching it.

On Saturday I drove just a few miles to a local car show, it was very cool in the morning and maybe 65 on the way home. My gauge was showing about 9'Oclock by the time I got home. The lines to the rear of the thermostat were so hot I could barely touch them, while the lines forward of the t-stat weren't even warm. I would have assumed the t-stat should have opened as my understanding of the gauge is that 9Oclock is just over 210 degrees.

[Targalid]

Get a hand held thermometer gun to diagnose your oil circulation problems. You should be able to find the culprit. The external thermostat should start to open at around 186F (86C), same temperature as the internal engine thermostat. I tested mine and it is fully open at 90C (195F). Maybe something is not assembled correctly?
https://www.amazon.com/Etekcity-Lasergrip-774-Non-contact-Thermometer/dp/B00837ZGRY/ref=sr_1_1_sspa?ie=UTF8&qid=1530556467&sr=8-1-spons&keywords=hand+held+thermometer+gun&psc=1

[dap930]

The external thermostat can fail, it did on my Turbo. I was able to replace the internal element with the same one that goes into the engine mounted thermostat. But getting the big cap off the thermostat housing can be a challenge.

[Ayles]

Originally Posted by dap930

The external thermostat can fail, it did on my Turbo. I was able to replace the internal element with the same one that goes into the engine mounted thermostat. But getting the big cap off the thermostat housing can be a challenge.

Thanks for the response. What symptoms did you see as it failed?

[shoooo32]

I had the exact same issue with my '78 SC. Our host sells a kit with a new Tstat, spring and aluminum washer.

It's not fun to do; I ended up removing the housing from the car so I could get the leverage I needed to crack it loose. Once apart you can spray it with brake clean to get any gunk that had collected. Depending on how long it's been since the Tstat stuck, you might want to flush the cooler lines.

[Ayles]

Interesting! Everything in the circuit is brand new except for the thermostat and the hard oil lines. Cooler is new as are all of the oil lines to the rear of the thermostat.

[Tremelune]

Definitely buy the IR gun to help diagnose. These thermostats work by always allowing oil to flow to the front of the car. When the motor gets too hot, the thermostat opens to allow cool oil back into the tank. Great illustrations here:

How External Oil Thermostat Works - Illustration

The thermostat is a real pain to get off most of the time, so if you can manage to get the internals out with it attached, you might save yourself some headache. It sure sounds like yours isn't opening.

[Ayles]

That’s a great link, seems like I need to go on bit longer of a drive one more time and recheck with an IR gun.

I dread removing the oil lines from side that of the t-stat that hasn’t been removed yet. Maybe just cut the nuts off and use the replacements from Elephant Racing.

[Ayles]

Got the car out today, did a 22 mile loop with some city traffic. Maybe 75 degrees tops.

When I got home the lines forward of the thermostat were hot! I used my new IR thermometer and took some readings.

Oil lines 180 ish, oil tank was 190, engine was slightly over 200. Starting to think I may have a mismatched sender showing a delta of around 40 degrees. The engine is not original to the car and appears to be the brass unit. Going to order up a sender for an SC of my year and give that a try.

[7783911]

I am in the same boat..I just redid my gauge to add numerics and to confirm i was indeed over 200 degrees after a spirited run,,,and no heat whatsoever past the external TSTAT...so i guess i have to pull it apart and clean, flush all lines forward and back, maybe install new plunger and spring. This is going to get messy on a 40 year old car...I intend to remove tstat/lines and trombone all together so i can flush on the bench. Is it possible to replace the internals without removing the whole unit..maybe thats step one and then if need be go to step two and do all the lines and the trombone?

[fintstone]

I suggest you start here (theory) External oil cooler thremostat

and then here (read the links in the thread as well). Rebuilding thermostat:

Oil thermostat rebuild / set

[7783911]

I ve read so many great threads...i think now its just time to tackle what will be a messy job...try to change plunger still installed and test again..if that doesnt work, comes off the car for bench test and then look at flushing all lines and trombone. Since there is hot oil in the lines pre thermostat I assume the internal thermostat is functioning..they are very warm and i can only assume that its not just heat transfer from proximity to the engine...I guess I could test that output too but spewing oil doesnt sound like a great project to do....

[fintstone]

I suggest you read the theory thread posted because you may not really have a problem. Lots of misunderstanding on oil cooling and expected temps here. Many, many threads/posts are just wrong.

200f is really not hot. If you are not getting hotter than that...much hotter...you are within normal operating conditions.

Removing and flushing lines is never needed unless your engine grenates and fills the system with metal.

[Ayles]

Got my new sender in the mail today and pulled the old one. The sender in the engine reads 150c on the side while the new one (selected for a 1982sc) says 200c on the side.

Since my engine is not from this car its entirely possible the sender goes to something else.

[fintstone]

Assuming you are talking the sender for the temp gauge...it needs to match the gauge, nit the engine. If you have an old style numbered gauge, it takes the 150c...if the newer style, 200c.

[Ayles]

Thank you! I have the newer no number guage like this:

[fintstone]

yes...Pretty certain your 150c is the one that goes with this upgrade (preSC numbered gauge)

https://www.pelicanparts.com/More_Info/PEL911TMPKT1.htm?pn=PEL-911-TMP-KT1&gclid=EAIaIQobChMIrd6Z36Cb3AIVSFqGCh0woA01EAQYASAB EgKHIvD_BwE

[SCadaddle]

Originally Posted by Ayles

Got my new sender in the mail today and pulled the old one. The sender in the engine reads 150c on the side while the new one (selected for a 1982sc) says 200c on the side.

Since my engine is not from this car its entirely possible the sender goes to something else.

Say Ayles,

I'm curious on how the swapping of the 150 to 200 sender works out for you, as that is on my list of things to do. My 82SC has the same instrument gauge as you depicted.

[Ayles]

As far as the technical aspect it was quite simple. The 150c sender came out quite easil, i ordered a new crush washer with the sender.

I would just wonder why your car is mismatched? My engine is not original to the car so that is what led me down this path.

[SCadaddle]

Who knows why mine would be mis-matched. The engine in my 82SC is correct 930/16 engine with a serial number that would appear to be original to the chassis, I'm certainly not the original owner yet the engine has one of the "brass" senders installed. I ordered the supposedly "correct" sender as you from our host for model year 1982. Just have yet to install it* and drive the car in the same HOT outdoor conditions to see where the gauge winds up vs. what my infrared temp gun indicates as compared to the old sender.

* The 200C sender our host sent me was obviously repackaged in the original packaging with tape and staples. Not happy about that, especially since the packaging has a clear plastic side that one can visually inspect the sender with all of it's markings by rolling it around in the package, yet this package was opened with a knife/razor blade/other sharp object then folded over, taped and then stapled closed.