470 question

[Blue t]

I have a 470 that is pushing the coolant into the over flow tank with out running hot. I have done a compression check and all cylinders are right at 140. I think I am going to try a new radiator cap and any other suggestions you may have.

 

[Rocky_Road]

Re: 470 question

I have a 470 that is pushing the coolant into the over flow tank with out running hot. I have done a compression check and all cylinders are right at 140. I think I am going to try a new radiator cap and any other suggestions you may have.

The correct (OEM) cap is only 14 psi...so I don't think this will help you.

I am sure that you will be hearing from other 470 owners about your problem!

Happy boating!

 

[stonyloam]

Re: 470 question

I have a 470 that is pushing the coolant into the over flow tank with out running hot. .

It is supposed to push coolant into the coolant recovery (overflow) tank when it is running. The reservoir should be full and the tank should have coolant in it to a level between the full and add level lines. When running the coolant heats and expands, the excess flows into the tank where it remains until the engine is shut off and returns to the reservoir as it cools.

 

[stonyloam]

Re: 470 question

The correct (OEM) cap is only 7 psi...

14 psi

 

[Rocky_Road]

Re: 470 question

14 psi

I am sure that you are right...the one I purchased from the Mercruiser dealer was 7 psi, but I have never trusted this dealer to do his homework as to my 470. The parts man always 'rolled' his eyes when I asked for a part that I needed.

I have corrected my post...!

Happy boating!

 

[Blue t]

Re: 470 question

I had the reservoir full and the over flow at the full line. It emptied the reservoir and over filled the over flow tank. I don't think it is a blown head gasket because there is no oil film in the over flow tank. I am thinking that the radiator cap is not holding 14 psi and it is pushing the coolant past the cap.

 

[stonyloam]

Re: 470 question

It emptied the reservoir and over filled the over flow tank.

OK, Well there is only so much coolant in there, so if it emptied the reservoir by pushing it into the recovery tank, it had to be displaced by air in the system. Go to Autozone and borrow their cooling system pressure test kit. I think you are probably pumping air into the coolant through the head gasket, even though your compression is OK. Good luck.

 

[Bamaman1]

Re: 470 question

+1 with stonyloam. The 470 cooling system operates just like a radiator--with a closed cooling system.

 

[EddiePetty]

Re: 470 question

.........and you may also be trapping air in the cooling system when filling.

Either jack the bow high when filling with coolant or run the engine a few minutes without the cap to expell trapped air.

 

[guyaverage]

Re: 470 question

I don't think it is a blown head gasket because there is no oil film in the over flow tank.

Thats not one of the typical tell-tales on this engine. Due to how this engine was designed, thats not something you are going to find to often, no matter how bad the head gasket is. Usually the other way around (coolant in the oil). If you pull the head, or look at the pictures in the Merc manual, it will make more sense why. By the time the head gasket got bad enough to let oil into the water jacket, the coolant would have belched into the lifter galley and caused all sorts of other problems first.