Coolant coming out of expansion tank

[poker player wayne]

Hello. New to boating and have a question. I got a Bayliner Capri 1950 for next to nothing from a friend's family. The friend had passed away. It has the AQ125A/270. I'm really good with mechanical stuff. I refurbished the expansion tank and heat exchanger. Replaced a bunch of stuff (fuel pump, carb rebuild, spark plug wires, and etc.). The local Volvo Penta shop has been real helpful with free advice. Anyway, took it out on Tuesday for a test run. The last registration sticker was 2001. I had a very experienced boater with me. At WOT the engine ran at 200 degrees and 5200 PRM according to the tach. At other settings it ran about 180. A few leaks at the heat exchanger and the exhaust hose at the manifold, but nothing that can't be fixed. My question is at WOT, coolant is coming out of the cap on the exp. tank. Not much, but I think it might be a concern. Any suggestions on what is causing this. I've searched the forums and didn't find anything. Thanks for any replies.

 

[Maclin]

Re: Coolant coming out of expansion tank

I see no mention of the raw water impeller being replaced, if it was not then it is time.

The cap itself needs to hold pressure on a closed system like that. Sometimes they are compromised and cannot hold the proper pressure.

It could also be overheating due to not enough raw water flow thru the heat exchanger, the raw water pump impeller is first suspect there.

Sometimes the exhaust manifold or risers can be rusted and clogged and restricting the spent raw water, that will cause overheating at higher speeds.

 

[Maclin]

Re: Coolant coming out of expansion tank

Welcome to iBoats! I just noticed your post count... :redface:

 

[poker player wayne]

Re: Coolant coming out of expansion tank

Maclin, thanks for the welcome. So can I assume (I don't like that word) from your comment that the engine is running too hot? Yes, I did replace the raw water impeller, but that was 3 years ago when I started this project. Could the impeller not work right sitting in one position all that time? It looks like the cap maybe is the original. I will go ahead and replace it just in case. As for as the exhaust manifold and risers, is there any way to check that?

 

[captmello]

Re: Coolant coming out of expansion tank

those engine can run close to 200 deg. under normal conditions, i believe they use a 195 deg thermostat, but that is just off the top of my head. The impeller should be replaced every two years as preventative maintenance. Your gauge may not be exact...

 

[Maclin]

Re: Coolant coming out of expansion tank

Wayne, 200 is getting hot for those, maybe not overheated but getting close. I meant more like "heating up" rather than overheating, the pressure rises as heat rises and the tank/cap needs to hold pressure, up to what they are specced for, before they vent. I do think the temp gauge should be a little more steady than that though. That much fluctuation in my opinion shows something going on that needs some attention.

I must add that 5200 rpm sounds a little high to me, and makes me want to pose a question: Does it do this at 4600 rpm? 4800 rpm? or just when pegged at 5200.

Generally low rpm temp problems that "go away" are impeller related, higher rpm temp problems are exhaust+riser related, and on Volvos the drive raw water routing connections (water neck, hose, etc.). If you can run at 4000 rpm on plane without the temps climbing rapidly then the drive connections are probably good.

Even with that, I would look at the impeller again, even when just sitting it is recommended to change them out every 2 years as the vanes can take a set.

No good way to check the spent raw water outflow thru the exhaust other than removing the riser and looking for clogged passages in it and the exhaust manifold. It sounds like the exhaust hose will need some looking at anyway, have to remove the riser I think to service that.

I can't remember if those drives had exhaust flappers, can't find my drawings I thought I had saved. But if it does (or did) those can melt and come apart from no water flow. You could look at the exhaust on the transom with the exhaust bellows removed to see if it is blocked by anything from a previous overheat. Rubber components that melted usually end up there.