Mercruiser 5.7 thermostat check balls

marife

Cadet
Joined
May 24, 2009
Messages
24
This was previously posted with no replies. I hhave decided to repost and rephrase:

Engine is a 5.7 1994 Mercruiser S//N OF353346, (recently overhauled).
The original thermostat housing was corroded and has been replaced with Mercruiser part # 87290A23 as per Service bulletin 99-2.

I have researched the threads and find contrary advice as to how to set the check balls. From tight to loose... Any reference to a Mercruiser Manual? I have them all and can find no reference as to how to calibrate...

Also can I replace the riser gasket from "two large/two small slots" to "four large"

Experts out there please input
Regards to all :
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
70,465
Re: Mercruiser 5.7 thermostat check balls

Ayuh,... I donno the spec, but the balls run pretty Loose...
Also can I replace the riser gasket from "two large/two small slots" to "four large"

You have hoses from the T-stat housing to the risers, so No...
The 4 large are for a different application...
 

Brentathon

Petty Officer 1st Class
Joined
Dec 29, 2009
Messages
385
Re: Mercruiser 5.7 thermostat check balls

For the "check balls", you simply tighten the little lock nut(s) all the way down, until there's no more threads..........in other words, you bottom-out the nuts. There's no "setting" or "calibration" for the balls.....they're only to provide a slight back pressure to the "extra" flow from the drive, so the cool water doesn't simply go right out to the elbows without circulating through the block and keeping the system topped-off. Issues with the check balls usually cause overheating at low rpm's.
 

marife

Cadet
Joined
May 24, 2009
Messages
24
Re: Mercruiser 5.7 thermostat check balls

In a way I guess they act as a thermostat except they work with pressure and not temperature? It sounds as if they were removed we would have excessive flow resulting in poor cooling, (just as a thermostat-less engine would do)
Thanks guys!!
 
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