Are Sierra thermostats OK?

[amuller]

I just got a Sierra 18-3543 stat to replace a stuck one that is presumably original or at least OEM. The Sierra unit does not have the vent or bleed slot identified in manuals as a design feature. does this matter?

[collectorinspector]

What is the motor in question?

BnC

[amuller]

1962 5.5 hp Johnson.

[beerman57]

You should update your general location, If you’re in the far south you don’t need a T-stat, Just restrict the water flow with a T-stat grommet/gasket and a stainless washer the right size.

[Casey Lynn]

These days I usually refrain from posting. Sometimes I just can’t resist debunking a flat-out "wives tale" however.
Yes, you do need a thermostat, regardless of where you are located in the country. After all …where is the cut-off between the "South" and wherever it is that you do need a thermostat? I just looked at a map and don’t see that line anywhere…….
Secondly, the thermostat was designed to bring the engine up to higher temperature (around 130-135F) at idle for a very good reason. That reason being that idle quality can be noticeably increased. Increased smoothness at idle due to the fact that a warmer engine at idle can be leaned more than a colder engine. Leaner engines idle better and do not leave as much unburned fuel on the surface of the water. You do not have a cold block and a hot piston with the increased wear associated with that combination either.
A secondary reason is to keep moisture build-up out of the engine at idle. Moisture build-up is not a good thing on the steel and cast parts of an engine.
Also……What size grommet or restrictor is it that that is being recommended here ??? Will the same size restrictor that will supposedly take the place of a thermostat and restrict enough water to warm the engine at an idle flow enough water to cool the engine at WOT? Don’t think so. Maybe the originator of that suggestion will be there to help you with the costs of rebuilding that engine when you stick the exhaust side of a piston due to an over temp.

Now, to answer the OP’s original question about the aftermarket thermostat. All I can tell you is that Sierra makes points sets that do not line up, carburetor kits that are not complete, and water pump impellers that do not physically fit properly in some engines but some of the guys in here swear by them because they (the parts) are cheap. You apparently get what you pay for so take this advice accordingly.

[dan-in-tn]

Sierra is apparently making a stainless steel thermostat #18-3543 (housing). They were not doing that a few years ago, but they also make their brass bodied thermostat #18-3553. That is part of the confusion. BRP/OMC use to make a brass bodied thermostat #378065, but it has ss to #5005440 which has a stainless steel body. The pellets appear to be of different materials, but I’m not sure what they are. Sierra’s looks like brass while BRP/OMC’s may have a coating on it.
Of course there is a price difference between the brass stat & the SS stat. Also a difference in the BRP/OMC stat & Sierra price. I personally prefer the SS stats regardless of the type of water run in. Small price to pay for better protection.
We have talked lately about our older motors not polluting as much when we can help it. Running a properly functioning cooling system (with thermostat) is part of what we can do as our responsibility. The motors run better this way as designed.

Dan in TN

[amuller]

Thanks for the comments. I am not in any doubt that thermostatically controlled cooling systems are a good idea. I would not consider leaving out the thermostat. (I’m in Minnesota where water is often cold, but would feel the same if I were in Florida.) Just looked on Amazon and the 18-3553 (brass) is $11.07 and the 18-3543 (SS, and the one I bought) is $17.18. Pretty noticeable difference. The BRP thermostat 5005440, which if the pic is correct is a brass one, costs $23.36. (All prices shipping included) I am not sure what the underlying failure modes of thermostats are. I see them failed open mostly but don’t know what’s going on. In general brass does not do well in sea water as the zinc fraction tends to go away.

I do object to paying $6-8 for the little mounting ring.

[beerman57]

Well, I’m 60 miles south of Tampa, and on the coldest winter day your motor is going to have no trouble getting up to operating temp. Plus I run in salt water (OH NO), but salt water on a T-stat would be my only worry about running in it. I always flush my motors, but a T-stat is just one big salt collector.

[collectorinspector]

quote amuller:

I just got a Sierra 18-3543 stat to replace a stuck one that is presumably original or at least OEM. The Sierra unit does not have the vent or bleed slot identified in manuals as a design feature. does this matter?

You will be fine not having a bleed.

None of mine have one. There may be a small bypass in the head casting near the thermostat somewhere…..or is that the 6Hp.

Good job in asking as thermostats are important.

Cheers

BnC

[george-emmanuel]

Fortunately we have Pappy and Dan giving experienced advice as well as Frank. To back up what Pappy said, my 1988 OMC 70 would not idle properly. Every local dealer tried different things with no success. So I took it to Pappy who found the t-stat defective. Most folks wouldn’t tie the two together…..but it does affect idle.

George

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