Mercruiser 470. Overflow tank

[jabfd]

Hi guys as many of you know I did my cam seals and upgraded to alternator on my 470 . My question is I filled the riser /res. with a/f. And left nothing in the over flow tank I took the boat out and the over flow tank has a/f in it now . The next day I open the radiator cap and I was a little low . I think the a/f is in the overflow will it suck it back in to the riser like a car also there is a 13 psi cap is that the right cap thanks for your help guys

 

[stonyloam]

Re: Mercruiser 470. Overflow tank

There should be a " fill to" line on the tank. Add antifreeze to the line. Then when you run the engine the antifreeze should expand and push out any air in the system along with any antifreeze overflow through the tube into the tank. When the engine cools off antifreeze should be drawn back into the engine through the tube, keeping the system full. The hose needs to be airtight at both ends or air will leak in and the antifreeze will not be drawn back in. Just like a car. 13 PSI should be OK.

 

[jabfd]

Re: Mercruiser 470. Overflow tank

There should be a " fill to" line on the tank. Add antifreeze to the line. Then when you run the engine the antifreeze should expand and push out any air in the system along with any antifreeze overflow through the tube into the tank. When the engine cools off antifreeze should be drawn back into the engine through the tube, keeping the system full. The hose needs to be airtight at both ends or air will leak in and the antifreeze will not be drawn back in. Just like a car. 13 PSI should be OK.

Ok I filled the res/ riser took it for a ride got back to the dock there was some a/f around the radiator cap and antifreeze in the overflow Iam waiting for it to cool down before I open the cap but I think when the radiator cap releases pressure it goes in the overflow and leaks a little from around the cap is normally

 

[stonyloam]

Re: Mercruiser 470. Overflow tank

Yeah, sounds like the cap is not making a good seal on the filler, so when it cools air is sucked in and the antifreeze is not pulled back into the reservoir. Might be time for a new cap. If the filler neck is bad, new OEM ones are still available. https://www.mercruiserparts.com/Sho...+MANIFOLD+ASSEMBLY+AND+EXHAUST+ELBOW+ASSEMBLY or https://www.mercruiserparts.com/Sho...=EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW(ALUMINUM) depending on which one you have.

 

[jabfd]

Re: Mercruiser 470. Overflow tank

Yeah, sounds like the cap is not making a good seal on the filler, so when it cools air is sucked in and the antifreeze is not pulled back into the reservoir. Might be time for a new cap. If the filler neck is bad, new OEM ones are still available. https://www.mercruiserparts.com/Sho...+MANIFOLD+ASSEMBLY+AND+EXHAUST+ELBOW+ASSEMBLY or https://www.mercruiserparts.com/Sho...=EXHAUST+MANIFOLD+AND+EXHAUST+ELBOW(ALUMINUM) depending on which one you have.

stony i took the boat out on sunday for a 40 mile round trip when i got back to the dock i checked the overflow it was empty yesterday i pulled the cap off the riser/res and it was a little low i still had some it res but not full. i saw a trail of a/f running down the riser it was dry like it was burned off from the heat hopefully that is my leak. i put this 13 psi cap on last fall because of the probalem i was having. Someone told me to drop the pressure. i would try the old cap if i could find it lol and i dont remember if it was 15 or 16 psi do you think that could be my problem. thanks again

 

[stonyloam]

Re: Mercruiser 470. Overflow tank

I don't think that the 13 or 15 psi is going to make much difference. You should be running in the 165-170 temp range so you are nowhere near the boiling point of the coolant, unlike a car that runs at 200+. As long as the cap is making a good seal and releases af into the tank it should be OK. Sounds like gasket on the elbow might be it. Just for the heck of it, you might pull the plugs and look to see if the insulators are all tan or brown in color. A white insulator would indicate a coolant leak into the cylinder ( steam cleaning the plug). If they look good, probably nothing more than a poorly sealing gasket. I think there is a dye you can put into the coolant to help find leaks if it gets to that point. 40 miles is a good long shakedown cruse LOL.

 

[jabfd]

Re: Mercruiser 470. Overflow tank

I don't think that the 13 or 15 psi is going to make much difference. You should be running in the 165-170 temp range so you are nowhere near the boiling point of the coolant, unlike a car that runs at 200+. As long as the cap is making a good seal and releases af into the tank it should be OK. Sounds like gasket on the elbow might be it. Just for the heck of it, you might pull the plugs and look to see if the insulators are all tan or brown in color. A white insulator would indicate a coolant leak into the cylinder ( steam cleaning the plug). If they look good, probably nothing more than a poorly sealing gasket. I think there is a dye you can put into the coolant to help find leaks if it gets to that point. 40 miles is a good long shakedown cruse LOL.[/Q

i replace the gasket on the elbow last fall and after i was done with cam seals i pressure tested the exhaust manifold everthing was good there but ill check the plugs and oil to make sure everything is good. thanks

 

[Scott Danforth]

Re: Mercruiser 470. Overflow tank

yes, there is about 6% expansion of the coolant when you heat it up. the overflow is intended to have about 15% capacity so that when it draws down, it pulls your AF mix back into the HX from the overflow tank.

if the cap is not sealing properly, it may not draw back.