Mercruiser 470 cooling system pressure question + heat ex-changer question

Hi all.

I currently have a 3.7 (470). Is it right that the cooling system when hot is so pressurized.

Unlike a car, when the engine is running you can remove the filler cap no problem, When its not running the pressure builds I know, but with my engine you couldn't because you would get a face full of very hot water and steam. It seems to hold a lot of pressure even when running.

Nothing pushes past the cap and into the header tank, The cap is 13 lb rated as advised in the manual. Would it improve if I lowered the caps pressure rating?

Heat ex-changer. The boat doesn't overheat but does run hot, about 3/4 on the gauge when under load. It currently has the standard 3" heat ex-changer and I notice that there is an upgrade available to a 4", I guess because this is a common question.

Is it worth upgrading and would the engine run much cooler, like 1/2 on the gauge?



Regards

Burkstar

Are you running the spec'd T'stat?
Before changing exchangers I would pull yours apart and pressure wash it thoroughly.
Depending on how many hours on the package, untold volumes of water have passed through the seawater side of the exchanger, and not all of it was likely clean.

Rod

Hi Rod
The stat is the correct one pat part purchased from a Merc dealer but not totally sure its working spot on, that can always be an issue so might get another one for the sake of it.

The cooling system is completly clear as I had the lot off recently and flushed it all through, also had the heat exchanger apart and made sure it was completly clear.

Still running hot though and at about 10 lb pressure??

When you say hot how hot?

If you have a guage that has NO numbers then you may be OK.

Those motors run typically at idle ~ 160 -170 degrees F

When running hard they can run as hot as ~180 -190 degrees F

They will for sure after shutting it off heat soak and get close to 200.........BUT once started it will cool right down.

Please try to get some actual temperature readings.

Also the way a typical marine cooling system works (yours specifically)

1. Water impeller in outdrive supplies water to heat exchanger and manifolds/elbows and voltage regulator. Is water pump impeller good?

2. Heat exhanger clean good?

3. engine mounted water circulation pump good?

4. elbow clean of scale and allowing water out of system. ( you can have plenty of water comming in but if it can not get out then you will over heat).

# 2 you allready answered..... so please answer as best as you can the rest.

True I have no exact temperature readings, I will try and work out a way to get those ??? (any advise)
From what you have said my motor really does run hot as standard so maybe I am worried about nothing.
All the other suggestions I have been through those and working perfectly and clean.

What about the pressure. Should my cooling system be under so much pressure when running. I am guessing from what you have said the answer would be yes as running at that temperature it would have to be a pressurized system as I believe water has a much higher boiling temperature when under pressure ????