Thermostat question for 84 Mercruiser 5.0

[ThomW]

Hey all.
I just have a question regarding the thermostat gasket for an 1984 Mercruiser 5.0 (228). Motor serial # is 6834170. I am replacing the thermostat on this motor, and noticed the gasket that was under the thermostat cover looks like this:

The kit I have came with a gasket that is similar but has a square cut out on the bottom tab.

When I look at thermostat housing, it has an opening that matches the second gasket, but the parts diagram I look at for my motor shows the first gasket.
Just want to make sure I use the correct gasket. If it is the first one, why does the thermostat housing have that extra square hole that matches the second gasket? Is that something later models used for something? Thanks!

 

[Bt Doctur]

It all depends on the thermostat housing and the cooling configuration.

 

[ThomW]

Alright. Well, as I said the housing has a notch out of it, like the second gasket. Looks like this.

The gasket that was on it, did not have the notch. What do you need to know about cooling system?

Which gasket am I supposed to use?

 

[Bt Doctur]

going by the serial number you do not have the spring loaded check balls nor the hose going to the elbow. You use the gasket with the cutout. This allows some cooling water to flow thru the manifolds cooling the rubber couplings untill the thermostat opens fully.

 

[ThomW]

Are you talking about the check balls in the valve assembly/thermostat housing? Like this?


If so, my motor DOES have this part, coming from thermostat to the rubber hoses.

 

[Bt Doctur]

. The housing with the T has 2 hoses from the T to the elbow/riser, then 2 hoses from the therm housing to the bottom of the manifolds.This type uses the closed slot gasket because the check balls allow cooling water to the rubber compnents

 

[ThomW]

Alright, and by the way, thanks for all the help with this! So, since I have the "T" with the check balls, I will use the closed slot gasket, despite the housing having the open slot, right?

 

[Bt Doctur]

The check balls allow water to exit the engine with the thermostat closed. once the thermostat opens the check balls close and water exits from the top of the therm housing out the hoses to the bottom of the manifolds

 

[Bt Doctur]

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[Bt Doctur]