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will a thermostat gasket leak coolant into the engine? #5333736 01/27/20 12:55 PM
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motor_oil_madman Offline OP
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I just had a new 5.7 MPI marine engine installed in my boat. I got 12hrs on it now and noticed that the 2 bolt flange gasket where it mounts to the engine is leaking just a tad on one side. Looks like the gasket blew out or got damaged some how. It doesn't leak when running, but I do notice a very small puddle of coolant that must be seeping out. It's very small the size of my pinky nail. lol The thermostat is on the very very front of the engine unlike my older 350 where it was 4'' back close to the carburetor. I wonder if it's separate on the new engine? it's just on a flat portion of the intake, if that's still the intake.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333739 01/27/20 12:56 PM
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motor_oil_madman Offline OP
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Is that portion of the coolant separate from the intake or am I leaking coolant into the lifter valley? This engine has roller lifters btw.

Last edited by motor_oil_madman; 01/27/20 12:56 PM.

2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333779 01/27/20 01:37 PM
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Chris142 Offline
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No it won't leak into the engine.


02 Wrangler Napa high milage 10w40
87 F250 Valvoline 15w40
07 fjcruiser Car lube plus 10w30
Z400 castrol T 10w40
Can am Maveric edge 5w40
57 case tractor Chevron sae30
Re: will a thermostat gasket leak coolant into the engine? [Re: Chris142] #5333795 01/27/20 01:53 PM
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motor_oil_madman Offline OP
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Originally Posted by Chris142
No it won't leak into the engine.


How come? Does that only happen when the intake manifold gasket itself leaks?


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333803 01/27/20 02:01 PM
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Spktyr Offline
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Originally Posted by motor_oil_madman
Originally Posted by Chris142
No it won't leak into the engine.


How come? Does that only happen when the intake manifold gasket itself leaks?


Pretty much, yes.

Intake manifold gaskets seal intake air and coolant (and sometimes oil) passages from each other and the outside, so when they fail, everything can mix. Thermostat housings only seal a coolant passage. Nobody routes intake air or oil through a thermostat housing, so no, a blown thermostat gasket will not itself let coolant go into internal engine passages where it isn't supposed to or allow coolant to mix with other fluids.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333848 01/27/20 02:56 PM
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Donald Offline
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Did they reuse the intake manifold? Thermostat housing cover?

You need to take it apart and see if either surface is corroded. New gasket and a tiny tiny amount of Permatex Ultra (black).

If this is raw water cooled you are only leaking some water from river or lake. If you are in the ocean and raw water cooled I would not want salt water leaking on my new engine.


2015 Ford F-250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333863 01/27/20 03:06 PM
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motor_oil_madman Offline OP
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No it was a complete drop in motor. It's closed cooling also. (Anti freeze)


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333906 01/27/20 03:54 PM
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PandaBear Offline
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Not sure about that specific engine but every single thermostat I see is between the coolant passage and the outside, not between oil and coolant. I'd be pretty [censored] if a leaking gasket other than head gasket will mix between oil and coolant (that includes intake manifold gasket).


"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah
Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333943 01/27/20 04:36 PM
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Donald Offline
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Originally Posted by motor_oil_madman
No it was a complete drop in motor. It's closed cooling also. (Anti freeze)


You will still need to take apart the cover on the thermostat housing and check both surfaces. Check for corrosion and flatness.

You could ask the engine supplier to provide new thermostat housing and cover. I have a similar but older version of that engine in my boat. I have taken apart the thermostat housing but cannot remember exactly how it looks.

You want to get this fixed so you do not get low on coolant.


2015 Ford F-250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5333997 01/27/20 05:35 PM
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eljefino Offline
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Yeah, why is this your problem? Go get it warrantied.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5334110 01/27/20 07:15 PM
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tiger862 Offline
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Put tablet in radiator that GM recommends. 8.00 on Amazon.


Tiger862
2018 Grand Caravan
Re: will a thermostat gasket leak coolant into the engine? [Re: tiger862] #5334309 01/27/20 11:12 PM
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Originally Posted by tiger862
Put tablet in radiator that
GM recommends. 8.00 on Amazon.


An engine shouldn't need any kind of stop leak. Fix it right and move on with life.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: eljefino] #5334310 01/27/20 11:14 PM
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Originally Posted by eljefino
Yeah, why is this your problem? Go get it warrantied.


Because I want to use it while the weather is nice. This boat has been in the shop most of the time I've owned it due to people taking 4 times as long as they told me it would take.

Last edited by motor_oil_madman; 01/27/20 11:15 PM.

2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

Re: will a thermostat gasket leak coolant into the engine? [Re: motor_oil_madman] #5337176 01/31/20 09:31 AM
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WyrTwister Offline
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If you had any coolant in the oil , the appearance of the oil would visually change , as it got worse .

Excuse me , did you say you had checked the fasteners that attach the tstat housing ?


Wyr
God bless
Re: will a thermostat gasket leak coolant into the engine? [Re: WyrTwister] #5337203 01/31/20 10:10 AM
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motor_oil_madman Offline OP
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Originally Posted by WyrTwister
If you had any coolant in the oil , the appearance of the oil would visually change , as it got worse .

Excuse me , did you say you had checked the fasteners that attach the tstat housing ?


I didn't check. You can see the gasket is damaged, that's why it's leaking.


2007.5 dodge cummins 6.7 liter. Chevron Delo400 15w40. 7000 mile or 250-300hr intervals.

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