hey guys ive had a high speed overheat problem since i got this boat 2 years ago.
It's a 78 mercruiser 898, with 305 engine, raw water cooled in a lake.
Since ive had it, i've replaced the raw water pump impeller 4 times just to be sure it was ok.
I replaced the hose from the drive to the transom and checked it for kinks, and made sure the connector that goes through the transom was clear.
I replaced the manifolds and risers using the restrictor gasket between the two.
Removed the heads and had them redone. All passages were clear in block and heads.
Replaced circulating pump on engine.
Took the engine out and check backflow flaps in y pipe
Removed the supply hose from the oil cooler, [which is clear of any obstructions] and checked for the minimum 3.6 quarts in 15 seconds, and got a little over 4 quarts. But on this test i didnt do it in the lake, i did it with the drive in a big tub of water.
And today I didthe clear hose test from the oil cooler to the stat housing and there was some air coming through the line, not tiny bubbles but a larger pocket of air running across the top of the hose.
I ran it up to 3000 rpm and the air pocket got a small amount larger but it seemed to be flowing lots of water but still overheated to 210 degrees.
Btw, thermostat is 143 degrees and always runs at least 160-180 and the temperature guage is accurate.
This engine uses the log style manifolds.
Sorry about the long post, just trying to give you all the info. Any help would be appreciated.
Richard
It's a 78 mercruiser 898, with 305 engine, raw water cooled in a lake.
Since ive had it, i've replaced the raw water pump impeller 4 times just to be sure it was ok.
I replaced the hose from the drive to the transom and checked it for kinks, and made sure the connector that goes through the transom was clear.
I replaced the manifolds and risers using the restrictor gasket between the two.
Removed the heads and had them redone. All passages were clear in block and heads.
Replaced circulating pump on engine.
Took the engine out and check backflow flaps in y pipe
Removed the supply hose from the oil cooler, [which is clear of any obstructions] and checked for the minimum 3.6 quarts in 15 seconds, and got a little over 4 quarts. But on this test i didnt do it in the lake, i did it with the drive in a big tub of water.
And today I didthe clear hose test from the oil cooler to the stat housing and there was some air coming through the line, not tiny bubbles but a larger pocket of air running across the top of the hose.
I ran it up to 3000 rpm and the air pocket got a small amount larger but it seemed to be flowing lots of water but still overheated to 210 degrees.
Btw, thermostat is 143 degrees and always runs at least 160-180 and the temperature guage is accurate.
This engine uses the log style manifolds.
Sorry about the long post, just trying to give you all the info. Any help would be appreciated.
Richard
