Internal Oil Thermostat Question

[Hokie6]

Hey guys - this is my first real post on my '81SC. I've been trying to understand how the internal oil thermostat works - in specific, how it blocks and directs oil to the cooler. There are two slots in the thermostat - upper and lower, and I'm trying to figure out how the slots mate with the internal machining to direct the flow. Seems like the oil would flow around the unit as there is no real sealing other than the O-ring that prevents it from leaking. Also, is there a proper orientation for installing in the motor (in other words, can it be install backwards?) Doesn't seem to be too much info regarding the internal thermostat that I could find.

I just did a top end overhaul, and had the dreaded oil leak from the thermostat even after using a new O-ring supplied with my gasket kit. This was the black O-ring, and now will be replacing it with a green O-ring. I want to get this right and don't want to go through the hassle of re-doing this with the motor in the car (or out of it!)

Thanks for the help -

[uwanna]

You could try to install the thermostat backwards, BUT it cant be done! The mounting
bolt holes are offset so that it only mounts one way.

[RSTarga]

I believe it has a wax insert just like the external thermostat.

[Hokie6]

Tnx - I think I see what you mean. It's not much of an offset, but looks like enough to prevent it from going in the wrong way.

Based on the following diagram, it looks as if the upper slot goes toward the OP switch? I'm working blind, so would like to get it aligned correctly the first time.





What are the wax inserts? Are they suppose to be inside the thermostat, or in the block? I'm trying to figure out how the thermostat interfaces with the passages in the block and prevents or allows passage of the oil to the cooler. I guess since the thermostat is indexed and can't be installed incorrectly, it's moot point unless something is missing -

[uwanna]

The unit that activates the thermostat is a wax filled, sealed metal bobbin. The special
wax inside expands as it gets hot and liquifies causing the cylinder/piston with the slots to move into place
(over coming a coil spring pressure) to change the oil flow.

[Trackrash]

Drop the thermostat in boiling water. You will see it open the slots. It's an easy way to check it's operation.

[Hokie6]

Did the thermostat test and seems to be ok. Just need to install the right way and hopefully stop it from leaking -

[Trackrash]

The bore in the case where the T stat goes was rough on my SC's motor. I smoothed mine with some fine sand paper (my motor was apart).

You might want to check if the bore has scratches or gouges. Some silicone grease (not RTV) may help as well.

[Hokie6]

Thanks - I will check that

[KTL]

uwanna is absolutely correct. The t-stat insert has its bolt holes clocked in such a way that you can only install it in one position that allows the holes to line up with the studs in the engine case.

Here's a good diagram that shows you how the oil finds its way through the engine.



When cold, the oil goes through a window that doesn't allow flow through the the oil cooler. Instead, the oil goes straight to the vertical oil galley that supplies oil to the warning light and the emergency/overpressure valve. That galley is intersected by the galley that sends oil onward to the crankshaft and then the camshaft housings.

When hot, the oil goes through a window that directs oil to the port in the engine case which feeds into the oil cooler. Oil goes through the cooler and then returns through an adjacent port which the connects to the previously mentioned vertical galley that feeds the warning light, overpressure valve and intersects the crankshaft galley.

The thing to keep in mind is that the t-stat windows allow one direction of flow and the other direction is blocked. In other words, when the oil is hot, yes it's finding it's way to the same galley as when the oil was cold. But the hot oil cannot "back-feed" into the cold path because it's a dead end with the cold window being closed on the t-stat.

[Hokie6]

KTL - thanks for the great explanation. I guess the clearance between the block and the thermostat is tight enough to allow the majority of oil to flow through the thermostat. When hot, I'm guessing there's a little that flows around and bypassing the cooler, but not enough to affect the operation?

Looks my O-ring will be in today, so hope to get that finished up. I'm going with the assumption that the upper slot goes toward the OP switch, so will try that orientation. Since I'm doing this blind (motor in the car and doing everything by feel), I'm hoping for it to align correctly the first time to reduce my frustration level!

[chrismorse]

One day, (after a thorough warm up), I ran the engine to red line passing another car and was greeted with a humungous blue cloud behind the car - I shut it off and coasted to the side of the road, with tons, (well many quarrts) of oil dripping off of the engine and rear of the car.

Some previous "mechanic" had over tightened and stripped the tiny thermostat studs in the block, so the thermostat pulled up out of the block and doused the engine/trans/exhaust/brakes - everything - in 10 quarts of oil.

These are tiny studs, threaded into the magnesium case. Do Not Let This Happen To you.

When in doubt, helicoil the little muthers

FWIW, the clean up was a classic "slippery slope" venture that involved a new clutch, wiring harness, seals, oil lines, axles, senders, and lots of rubber parts.

chris

[Flat6pac]

For the past several years I have been putting a bead of 574 above the O ring because the O rings have been allowing oil to pass.
Bruce

[Hokie6]

An update on my thermostat leak -

I found that the upper slot in the thermostat does indeed point toward the OP switch, and the thermostat dropped right in. Unfortunately it dropped right in meaning the O-ring didn't provide the tight fit I was expecting. Really didn't want to take a chance on it leaking and going through all of this again, so added a second O-ring at the top to help seal between the block and thermostat and a little sealer to at least make me feel better about it Was careful not to tighten too much, but enough to compress the O-ring.

Only about 25 miles on the test drive, but so far, so good. My OP is a little high (~4.5 @ 2500) probably due to the restrictors, but so far no oil leaks and running well.

Thanks for all the help -