"Custom" thermostat?

[holmen78]

The water comes in left corner of exhaust cover (see picture), then it goes into the block through 3 bigger holes (yellow in picture). The block fills up and water goes out through thermostat on top when warm. The tell tale outlet is at the bottom right of exhaust cover . Roughly explained cooling system.

[mitch184]

That picture says a thousand words...thank you.

So while the thermostat is closed, how does the incoming water pressure from the water pump bleed off? I would imagine it’s not good to run higher rpms while the thermostat is closed if that pressure is hitting the thermostat itself??

how does the pressure relief valve play into everything?

[boscoe99]

That picture says a thousand words...thank you.

So while the thermostat is closed, how does the incoming water pressure from the water pump bleed off? I would imagine it’s not good to run higher rpms while the thermostat is closed if that pressure is hitting the thermostat itself??

how does the pressure relief valve play into everything?

The thermostat is dimpled so that air can be bled off as the water enters the block and displaces the air. When the block is filled with cold water some of that water will bleed off via the dimples.

At the same time water is being bled off to the tell tale port.

If and when the water pump creates excessive water pressure (say at a high engine RPM) the pressure relief valve will open. Either with the thermostat closed or with the thermostat open. But moreso when the thermostat is open since the motor is running and creating lots of power. Pumping lots of water. More than is needed to cool the motor. The pressure control valve diverts water and keeps the pressure under control.

[mitch184]

thanks for the explanation. So the pressure valve is a valve from the block cooling system, pre-thermostat, out to the t stat housing that lets it go down back into the motor. Essentially the thermostat and the pressure relief do the same thing... just one via temp and one via pressure.

There’s not much cooling done after water passes thru the thermostat or the pressure relief valve though I’d imagine.

[99yam40]

I believe the PRV dumps cold water out into the exhaust stack before it runs thru the block

[walleye1]

I have an idea on this. Was the original owner and scuba diver?

I've noticed more and more scuba divers doing this. They Jerry rig their motor up to pull hot water out of the engine. They run a hose into a 5 gallon bucket. When they get back in boat from a cold dive they dump the hot water on their wet suits to warm up.

Don't need a lot, just enough to fill a bucket or two. And it's useful for lion fish stings and stuff.


Very interesting.

[holmen78]

I believe the PRV dumps cold water out into the exhaust stack before it runs thru the block

Not on this engine. I think PRV is not operating at all except for extreme conditions. Water exiting PRV and thermostat goes between cylinder head cover and gasket down to exhaust, before that water has gone through block and cylinder head

First pic is where water goes after block is filled.

It then pours around the chambers on its way down through 2 holes to the outer side of cylinder head(pic 2).

In pic3 the water goes up to the thermostate/PRV assembly between head cover gasket and cylinder head.

[mitch184]

Ok. So by moving the tell tale to the thermostat housing... it’s going to create more water pressure in the block before the PRV opens, remove more air from the block and be a strong sign of when the thermostat and/or PRV opens. Cause the tell tale pressure will increase a lot.

adversely it’s going to pull pressure and flow away from water going to the cylinder head cover and exhaust. Possibly increase cylinder head and exhaust temps?

that sound about right? I’ll probably get a new stat housing and change it back regardless.... just curious on the theory/thought process at this point.

and no clue whether he was a diver.

[holmen78]

I would buy a new thermostate/PRV cover and unplug original tell tale like it is designed to be. Like you have it now only escape route for excess water pressure is through PRV if motor is not hot enough for thermostate to open. The tell tale is like a pressure relief on the “cold” side of cooling system, like 99yam40 said.

The cooling in the exhaust housing is none if the thermostate isn’t open.

I really hope there isn’t any other mods inside that could explain the modified tell tale solution.

[TownsendsFJR1300]

I would buy a new thermostate/PRV cover and unplug original tell tale like it is designed to be. Like you have it now only escape route for excess water pressure is through PRV if motor is not hot enough for thermostate to open. The tell tale is like a pressure relief on the “cold” side of cooling system, like 99yam40 said.

The cooling in the exhaust housing is none if the thermostate isn’t open.

I really hope there isn’t any other mods inside that could explain the modified tell tale solution.

The "tell tale" is NOT a pressure relief, period. It is simply is a visible way to show that water is making it to the power head.

The PRV valve opens when there is too MUCH water pressure inside the engine and releases that excess water/pressure.

And water is always pumped to the exhaust..


I do agree thou, replace the cover, inspect thermostat and PRV. Lastly, repair the "tell tale" ("Cooling water pilot hole" as shown below) system back to stock and everything functions as designed..


The water flow chart for my F150. Yours should be very close if not the same:

[holmen78]

Yes walter is always going to exhaust. It comes in through exhaust guide under power head. In exhaustguide there are some passages that cools the exhaust tuner with water that never enters the block. I regret that I didn’t analyze the cooling system further when I had it open. This is interesting when you start to think about it.

[99yam40]

dang you are joining in the someone else on another thread about what some write?

[TownsendsFJR1300]

dang you are joining in the someone else on another thread about what some write?

Not dragging you into anything 99.

Just pointing out to a ***** about his "half assed" responses. He doesn't have a clue what he's talking about..

[TownsendsFJR1300]

Yeah right. And throwing up a flow chart of a 4-stroke is full-assed?

That post was meant for the *****.

Not for you Holmen98, my apologies..

[BQUICK]

I was trying to remember who on here ran a hose like that not too long ago.
And though maybe you had sold the motor to the OP

Yeah, that was/is me. Made a big difference in cooling since my lower crossover was clogged and leaking from corrosion.