Some Comments on Thermostats

[ndutton]

One a side note, can you tell us what that ducting in front of the manifold is for?

Exhaust hot section heat shield?

Wristwister, my RWC engine ran between 100° and 120° with a functioning 140° Holley 3 spring thermostat. I did the vinegar soak and stove top test but still the same result. Low temp is not necessarily conclusive that the T-stat is dead.

[Marian Claire]

Makes sense with the exit hose from the manifold heading in the same direction.
Dan S/V Marian Claire
Edit: I believe wristwister has a Tartan. It may be one with the A-4 mid-ship and off to port with the standpipe exhaust so having the exhaust exit the flywheel end would make sense.
Slow day here in the mtns.

[wristwister]

Thanks for the quick advice folks. Yes, that's a heat shield. Like Marian said, it's a Tartan 30 with the engine up front just behind the mast. The exhaust runs forward and out.

ndutton, I'm curious how you'd be running at ~100 with a known good $140 thermostat. Bad temp sender? I my case, I've been running consistently ~180 for years, then one day started registering no higher than ~120.

Yes, I agree I should pop out the thermostat, test it, do the acid soak etc. I plan to do that. It's just that I've learned the hard way that anything can happen on even the simplest of tasks on a 44 year old marine engine. Busted screws, bad fittings, other weird anomalies. I just want to be fully prepared before I crack that first nut to prevent the boat being out of commission for too long once I get started.

[JOHN COOKSON]

Remember the lower the resistance in the sending unit, as the engine heats up, the higher will be the gauge reading.*
So if there is resistance in the circuit temp sending unit -> gauge the gauge will read abnormally low. Edit: Corrosion on the wire end fastener will have the same effect.
To test for resistance in the boat's wiring let the wire loose at the sending unit and loose at the gauge then connect a jumper wire at one end and measure the resistance at the other two ends. S\B zero ohms.
*By way of illustration, as best I can recall at the moment, the spec for my temp sending unit is something like 550 ohms at 70 degrees and 30 ohms at 212 degrees.

TRUE GRIT

[ndutton]

curious how you'd be running at ~100 with a known good 140 thermostat. Bad temp sender?

I cannot vouch for the accuracy of the gauge and sender at the time but the stove top thermostat test was done carefully and it began to open a little before 140°, was fully open by 140° so the stat was performing to spec.

I'm not so sure the front of the head right next to the thermostat housing (late model) is the best place to sense temperature.

[wristwister]

OK folks, the next chapter of the Tartan's running-too-cool saga:

I popped out the thermostat, it's definitely the single-acting with the bypass, but the bypass has no restrictor valve. The thermostat was pretty gunky, and closed. I did the vinegar soak, cleaned it up, and tested, opening at 160 just as it should. It definitely wasn't stuck open and likely was working fine.

So ... any ideas why the engine is running so cool? Could it be because there's no restrictor in the bypass loop? This would be weird, because it's been running at ~180 for the last few years, and then one day last summer it just started running cool, going no higher than 120. Ideas?

[JOHN COOKSON]

O
So ... any ideas why the engine is running so cool? Could it be because there's no restrictor in the bypass loop?

Maybe i'm not reading this right but no restriction in the bypass would cause the engine to hotter not cooler. The bypass is just that: water goes around the engine via the bypass and not through the engine thus not cooling it. Said another way restricting the bypass causes the engine to run cooler.
Did you check the wiring for resistance? Post #34.

TRUE GRIT

[JuniorAtomic]

Soot in thermostat

Hello guys,
Joined the forum to learn how to maintain properly my Atomic 4 which I have on Coronado 30. I'm new to the engines so please don't throw stones in my direction I have few issues with my A4 among others is milky oil/moisture in first two cylinders.
I'm trying to understand how would the soot/grime get into the thermostat per pics attached. Could it be the manifold has a crack sipping water in mixed with exhaust gas when operating? The engine is raw sea water cooled.

Any thoughts or ideas?

[scratchee]

Hello guys,
Joined the forum to learn how to maintain properly my Atomic 4 which I have on Coronado 30. I'm new to the engines so please don't throw stones in my direction I have few issues with my A4 among others is milky oil/moisture in first two cylinders.
I'm trying to understand how would the soot/grime get into the thermostat per pics attached. Could it be the manifold has a crack sipping water in mixed with exhaust gas when operating? The engine is raw sea water cooled.

Any thoughts or ideas?

Do you know the compression in the cylinders? Milky oil and moisture could mean a ruptured head gasket between those two cylinders with issues. That could also account for the dirty thermostat. You can get an inexpensive compression tester online, or borrow one from an auto parts store. It's an easy test to do.

I recommend you start a new thread on this issue.

[sastanley]

Jr.
Plus One...start a new thread on your particular issue so we can keep it all isolated to you! And, welcome aboard.

[JuniorAtomic]

Do you know the compression in the cylinders? Milky oil and moisture could mean a ruptured head gasket between those two cylinders with issues. That could also account for the dirty thermostat. You can get an inexpensive compression tester online, or borrow one from an auto parts store. It's an easy test to do.

I recommend you start a new thread on this issue.

Thank you for your reply and a suggestion. Now that I've been on this forum for few days I see that I should have probably started with oil changes and a compression test. What we did was to pull out the engine from the boat to take a look at it closer in a garage...
The moisture in 1,2 cyl is an ongoing issue that was fixed temporarily couple years ago by a local mechanic and now looks like it's back and I have some ideas on what is causing this which I will share in relevant Discussion Topics threads

[JuniorAtomic]

Jr.
Plus One...start a new thread on your particular issue so we can keep it all isolated to you! And, welcome aboard.

Thank you and will do!

[Captain Kirk]

installing MMI Thermostat, 150 degree (late model double-acting)

a hint for the community on installing a MMI Thermostat, 150 degree (late model double-acting). What appears to be a simple job becomes more complicated when having to remove the alternator to get at the hoses for the bypass valve and remove them to take the thermostat housing off. It took me 3 tries to get the new thermostat centered in the head so that the housing wouldn't leak. What worked for me on the third try was glueing the thermostat to the flange inside the housing with a tiny amount of Permatex seal-a-gasket, and clamping it overnight. On this attempt when I turned the housing with the thermostat attached, I was able to center it in the head so that it no longer leaks. I can think of no other way to center it without trial and error, because the 'hole in the head' (no pun intended) is larger than the diameter of the thermostat. The flange of the thermostat just fits in the lip of the housing, so glueing it in there just makes sense. It would be great if Ken could supply a tiny amount of Permatex seal a gasket for just this purpose.
I used the aviation Permatex for the gasket itself and even put a thin layer on top of the gasket (just to be sure) even though it's not recommended. With having to take the alternator and short hoses apart the whole process is very time consuming and frustrating if the housing leaks after putting it all back together again which is the only way to test the seal. You simply can't tell if the thermostat is centered until you start the motor.
Ken doesn't like the idea of using Permatex on the top of the gasket and the housing lip because of difficult cleaning at maintenance time. Personally I'd rather apply a little elbow grease to cleaning than having to re-install the thermostat and housing. Just my thoughts in case anyone else comes up against this issue.

[ghaegele]

Does MMI Thermostat eliminate need for bypass back pressure?

I am installing the MMI thermostat and Moyer's comments make me think it eliminates the need for any restriction in the by-pass loop. "This design also eliminates the need for any additional restriction in the by-pass loop." Which makes sense as the thermostat when fully open will close off the bypass. (My thermostat housing is in good shape.)

I assume that means I can remove the "Check Valve" with the 2-3 PSI back pressure installed in the bypass loop. I don't see that it does any harm to leave it in place, but it does make removing the thermostat when winterizing or doing an acid flush a bit of a PITA. Or does it mean any restriction in addition to the Check Valve?