over heats above 3500 rpm

[barmahn]

I have an 87 bayliner with a Volvo 125 in it and here is the issue that I have been fighting with.
The engine runs great and stays cool while I have muffs on it running water through it that way. Once I take it out on the water it will start to heat up and stop pumping water in the fresh water system when I have it above 3300 rpm's or higher. I have replaced the impeller housing and impeller for the fresh water. Have replaced the nipple on the lower unit as it was all corroded between the housing and hose. Once I did that it ran great all day up and down the river at full speed. Stopped and parked for a while on a sand bar and then outdrive didn't get into the sand bar only front of boat did. Took it back it worked great. Next time out it overheated when I had it above the 3300 rpm's. It just stops pumping water I think as I can't drive the boat and take the cover off and then check the water flow on the fresh water part of it. It has a cap that I can take off and clean a screen if it is plugged up with weeds before it goes into the heat exchanger. I have taken the heat exchanger apart and put new gaskets on it also after I took it apart and cleaned it even tho it wasn't clogged up. Any help would be great on what to look for next. Seems I do one thing and it works great for a day and next time I take it out it wants to overheat as it stops pumping the water on the fresh water system. The closed system is full of antifreeze and water mix. Holds psi with psi tester and cap holds air also. So don't think it is a head gasket issue.

 

[kenny nunez]

There is a “O” ring between the lower gear case and the intermediate housing. It seals the water passage where the lower swivels for steering.
All you need to change it is some allen wrenches. You should also drain the oil first.
What happens is air enters the the in coming water when the boat planes out and the “O” ring is not submerged.
Sierra # 18-3888 Lower gear unit seal kit.

 

[Scott Danforth]

And just above the Oring is the white metal fitting the hose connects to that should be replaced every few years because it corrodes

 

[barmahn]

And just above the Oring is the white metal fitting the hose connects to that should be replaced every few years because it corrodes

I have replaced the o rings and the white nipple/ elbow and still over heats when above 3500 rpm and out on plane. Any other ideas. Even had heat ex changer cleaned this past weekend and still overheats.

 

[barmahn]

There is a “O” ring between the lower gear case and the intermediate housing. It seals the water passage where the lower swivels for steering.
All you need to change it is some allen wrenches. You should also drain the oil first.
What happens is air enters the the in coming water when the boat planes out and the “O” ring is not submerged.
Sierra # 18-3888 Lower gear unit seal kit.

Did those along with the hose from the transom to the nipple/elbow on lower unit. Had heat ex changer cleaned and still over heats when out on plane.

 

[barmahn]

I have a 83 byliner with a 125B volvo motor in it. The boat runs great when not on plane and runs great when out on plane. My issue is that the boat will overheat when out on plane. Here is what I have all replaced in it to try and fix it. I have replaced the raw waterpump and housing, the elbow on the 270 outdrive, the hose from the transon to nipple, the 3 o rings on the lower unit. If not on plane the boat will run a cool 190. I just had the heat ex changer cleaned as the guy said that there was a lot of crap in it. He said that should fix the problem. I just thing that it is not picking up the water once it is out on plane. When I tried to run the boat in a tub that goes up half way up the lower unit it wont suck the water up. But with the boat in the water it will suck it up. Take the cap off of the heat ex changer where the screen it there is no water when out on plane. Can a heat exchanger cause this issue. The boat mechanic seems to be just wanting to throw more money at it as it seems to me. I have had a few people tell me that they have had this issue with no water pickup and they put a thru hull pick up and did away with the pickup from the lower unit and solved their issue. Any other ideas?????

 

[Scott Danforth]

I have replaced the o rings and the white nipple/ elbow and still over heats when above 3500 rpm and out on plane. Any other ideas. Even had heat ex changer cleaned this past weekend and still overheats.

maybe change from the raw water pump from the F5B pump to the F6B. direct interchange, 25% more flow

 

[barmahn]

maybe change from the raw water pump from the F5B pump to the F6B. direct interchange, 25% more flow

the whole housing or just the impeller?

 

[barmahn]

maybe change from the raw water pump from the F5B pump to the F6B. direct interchange, 25% more flow

Mine is driven by the timimg belt on the 125B motor. Is it the whole housing your talking about or just the cam inside of it along with the impeller