How does the thermostat work?

[oneblueyedog]

I cleaned my thermostat today and I was curious about it. I always had a hot engine before the rebuild. Too hot acutally. I was thinking it was mis timed on the right bank (Stud replacement without resetting the timing- someone replaced the pin back in the same bore because I found an X scibed on the cam sproket.)

But after reading the oil circulation page on the fische, I found that this crucial valve, if misfunctioning, will keep every drop of oil from reaching the cooler.

I took it apart (easy) and found little wear. I remember reading years back that the units have a wax valve inside. I looked at this brass thing and saw some rubber fragment coming out of the junction between the steel pin (looks like a nail head )on the brass housing. The pin wouldn't budge. I heated it up and oil kinda bubbled out around the perimeter of where the pin goes in. I wanted to find out why this broken tidbit of rubber was wedged in between the pin and the housing. The heat finally let the pin move and I played with it up and down. I put it in the freezer and it froze it in place as before. I heated it up again to see how far the pin would telescope out. It came out and sure enough it does have a tapered end like a nail and wax residue was on it.

But mechanically I can't figure out what it's supposed to do. The spring of the thermostat keeps the valve sleeve up against the top of the aluminum housing. In the top of of the sleeve is where the wax device is nestled.

When the thermo is cool the valve is open at the top port on the side.

Does the spring get Hot and let the sleeve come down to let the oil go through the bottom port? If this is so what do you need the wax device for?

I can't imagine the wax device pushing the sleeve down, when I warmed it the pin stays stationary. I can move it manually. What's that pin for?

I'm suspecting the wax device is shot because that little tidbit schard of rubber was a seal of some kind that was KAPUT.

Anyone know the function of the wax device? There's one in the fender oilcooler circuit too.

Thanks for any help.

[rw7810]

put thermostat in a pan of water on the stove and heat to 180-190 degrees. The sleeve should move (can't remember which way), but it should open up a port for the oil to flow to the cooler. When it cools, the sleeve closes the port.

[jgparker]

I've had two oil thermostats go bad in the past few years, so don't belive anyone who tells you they never fail. Try Bob's pan of water trick, the movement is obvious if the part is working.

JP

[oneblueyedog]

Cool ! Will do and will share details.

Wulf

[Wayne 962]

They can get rusty/corroded and fail - I've seen one or two that are stuck shut...

In general, they rarely fail though...

-Wayne

[oneblueyedog]

I did some cooking. The kids came a runnin' in wondering what's for dinner. I said molybdenum disulfide. They said peweee.

I boiled the thing. The port to the cololer did not open. Not a sliver. I surmise that the wax device must push the sleeve down in some way. I don't see how though.

The big spring didn't shrink either. This would seem most logical to what I know (like a Detroit auto).

So it definately opens up under just general heating and not hydraulics?

[Pat S]

Definately opens...
See this thread for a quick T-stat cooking lesson.
engine oil thermostat test photos

[oneblueyedog]

I really appreciate the comparison thread. I had mine at a full boil!

It's a great testimony to the engine's durability. I'd been running it like this for 6 years. I even replaced the thermostat up to the loop cooler. I never thought to look at the engine thermostat. I'd skip driving it during the hot months because the temp would soar to the edge of the red on our 108° days in Dallas. Thus, junking the oil.

On teardown I found very little wear though. The bearings were worn but not galled. The journals all measured within the spec range. The Intermediate shaft was the only brearing showing brass.

The fan was the only thing cooling it. I was always envious of my friends 79SC in that his guage never went above the mid mark. I know why now.

Awesome!

[kstylianos]

Good catch. I had a very similar overheating issue.

I even went as far as replacing the semi-crimped brass lines with the Elephant lines with little or no improvement.

Turned out to be the internal t-stat.

IMHO: One of those items that should be replaced while the engine is out.

[Doug E]

I just replaced mine (thanks to Charlie) while the engine was out of the car ... at $75 from Pelican I don't see how you can go wrong.

Now I can't wait to get it back on the road to see if that was the cause of my high temps all along.

[echrisconnor]

Can this thermostat be removed with the engine in the car (without removing the CIS system)?

If so, how? Anyone have any pictures of access?

[oneblueyedog]

Yes you can but you must do a partial engine drop. I think there is an extensive article on the Pelican site. Or do a web search -partial engine drop 911.

I know this because I had to replace the o-ring seal on the t-stat.