f_inscreenname

Hey
Just had an issue with the tiniest piece of rust flake blocking the tiny bypass hole in my thermostat housing top gasket. Without the bypass hole the water pressure built up so bad that the back of the waterpump started leaking.
After looking I found that you can get a open, restricted and an closed gasket. Which one should I use?
BBC with merc raw water cooling. Have really tall risers also.

mike tkach

iTrader: (3)

it depends on what year and style your engine is.merc made a lot of changes through the years so you always need to use exactly the same as what it had to start with.

f_inscreenname

The motor is an off shore race motor. Just using the cooling system off a 330 merc 454. I have custom very tall exhaust risers and don't think back pressure is going to be an issue. Would like to have a lot of water flow out the exhaust all the time if possible with the open gasket. Running a 140 thermostat

35fountain

I use the one with the hole in it. My engines have a brass tee fitting on the thermostat housing that is the bypass.[ATTACH=CONFIG]542560[/ATTACH]
The hole in the gasket keeps a slight constant flow through the housing.

f_inscreenname

Mine looks like that but don't have the T. Just a cap with 2 outlets for the manifolds.

35fountain

Since you need constant water flow to your exhaust manifolds and you don't have the bypass tee then I would use the open gasket. This way your manifolds won't go dry. The one with the small hole is not enough bypass water and that's probably why you had high water pressure.