Thermostat Gasket?

wyrman

wyrman

Well-Known Member
Jul 12, 2012
1,921
Tri-Cities, Wa
Boat Info
2007 310 Sundancer
Engines
Twin 350's, V drives
2003 Fisher 17 aluminum
90hp Honda 4 stroke
Just wondering if this gasket needs replaced.
Just kidding, was actually wondering how important the original gasket is with the metal grommets on the sides are.
I picked up a t-stat and a gasket at NAPA, and started thinking they must be there for a reason.
 

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So they can charge 3x the normal price? :)

No idea if needed. My old gms in my chris craft I just used "form a gasket." Things are so complicated these days.
 
techmitch said:
They are imperative IMO.
Click to expand...
Ok, thanks. I figured as much, but wanted to confirm it.
Our problem here is we have to order everything online. There are no stores locally that I know of.
I did get the t-stat and gasket for $10 at NAPA. They want $30 plus for the mercruiser stat online.
I only took it off to make sure there wasn't any impeller pieces in it from last year. There wasn't.
 
Your original post says "a" T/stat. With twins, are you not replacing both? Also, although the MC price does seem a bit high, without doing the shopping myself, on a newer boat like yours, I would advise the O.E. stuff with something like this.
 
techmitch said:
Your original post says "a" T/stat. With twins, are you not replacing both? Also, although the MC price does seem a bit high, without doing the shopping myself, on a newer boat like yours, I would advise the O.E. stuff with something like this.
Click to expand...
I hate it when someone calls me out. lol, just kidding. Everything has been working perfectly, I really hate to mess with that, but I will go get another t-stat and replace both. I might be wrong, but the t-stat should be ok with NAPA, there's nothing special with those.
I did order the gasket, and it is a two pack, and it is really easy to remove.
I appreciate the answers.
 
No calling out/bustin what so ever!
What brought us to the T/stat in the first place.
Glad you got the MC gaskets and I got no problem with NAPA but they surely have at least 2-3 different brands of T/stats. Which did you get?
 
techmitch said:
No calling out/bustin what so ever!
What brought us to the T/stat in the first place.
Glad you got the MC gaskets and I got no problem with NAPA but they surely have at least 2-3 different brands of T/stats. Which did you get?
Click to expand...
I'm kidding about the calling out, I appreciate it. The only reason I took it apart was I had an impeller fail last summer.
It wasn't due yet, but it was an aftermarket, so i guess it was due. I'm replacing it with OEM. I tracked most, if not all, pieces down, but since it's sitting at home right now I decided to check and make sure there isn't any pieces at the t-stat while it's out of the water, it was all clear. Just makes me feel better knowing there's not any more pieces floating around.
 
I would guess that is true also, but actually, the brass grommets provide the ground path for the temp sensor and the high temp alarm switch which are screwed into the t-stat housing.

On last boat, installed a bond wire between the t-stat housing (drilled and tapped a hole in thick part) and the engine. Never had a problem with temp gauge / alarm and used the std $1.50 t-stat gaskets form autozone there after.
 
As mentioned in a couple posts above, a gasket with a grommet is absolutely needed for the ground for the sensors in your t-stat housing. Unless you do something like Bill did.

Best to put the gasket on dry - or at least be very stingy with the goop if you actually need it for a rough surface.
 
Yes, I knew there was a reason for the grommet's, I remember that when I last changed the thermostat on my 4.3. Dennis confirmed, if you don't put in the right gasket on, the temp sensor will be out of whack.
 
BillK2632 said:
Yes, I knew there was a reason for the grommet's, I remember that when I last changed the thermostat on my 4.3. Dennis confirmed, if you don't put in the right gasket on, the temp sensor will be out of whack.
Click to expand...
The 2 wire sensor that reports coolant temp to the ECM is not affected by this. That sensor is just a variable resistor and doesn’t need to be grounded.
the ECM reads the resistance across the terminals.

However the single wire temp sensor that reports coolant temp to the dash gauges needs a good ground to operate properly.
 
The grommets are an interesting way of doing things. You'd think the mounting bolts would be sufficient. I have the ability, but not the desire to add a ground strap so I can use the cheaper gasket, this isn't something that gets changed to often.
The proper gaskets will be here Tuesday, I'll get other things done until then. I don't use sealant on stuff like this usually.
 
wyrman said:
The grommets are an interesting way of doing things. You'd think the mounting bolts would be sufficient. I have the ability, but not the desire to add a ground strap so I can use the cheaper gasket, this isn't something that gets changed to often.
The proper gaskets will be here Tuesday, I'll get other things done until then. I don't use sealant on stuff like this usually.
Click to expand...

Some of the t-stat housings are 2 piece with a gasket above and below the main body that hold the temp sensors, effectively insulating it, electrically, from the cover that has bolts into the top and manifold where the bolts ground. Actually it was a pretty effective method without needing a ground strap.
 
Espos4 said:
The 2 wire sensor that reports coolant temp to the ECM is not affected by this. That sensor is just a variable resistor and doesn’t need to be grounded.
the ECM reads the resistance across the terminals.

However the single wire temp sensor that reports coolant temp to the dash gauges needs a good ground to operate properly.
Click to expand...

Actually, not all Mercruiser engines are ECM controlled. Both my temp sensor and hi temp switch are 1 wire.
 
I used a cheap thermostat and gasket and it didn't fit properly and it leaked. Just use the factory MerCruiser gasket with the brass inserts for temp. Just don't use cheap knock off shit unless you like doing things twice, learned my lesson
 
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