Diagnostic help needed

[Brose]

My 1973 X-18 is running just fine, thank you. However, my boating pleasure quotient is directly correlated to the boating pleasure of my parents, who bought my old boat -- and it is overheating.

It's a 1980 SeaRay with a 260 Mercruiser. The boat heats up and cools down unpredictably while underway (mostly at speed). The lower unit impeller has been replaced. Compression check came out fine. Thermostat is good. I don't know where else to look???

Water pump?
Cracked block?

I know that this post doesn't necessarily belong here but I'm a Donzi owner in need of advice!

[Rootsy]

good beginning point scott! bubbles are bad...

On older merc stuff (#1 and older R) i've also seen that hose from the transom assy to the motor circulating pump delaminate inside and collapse.. you'd never know it from the outside... and it can drive you nuts...

also, when was the last time the hose was replaced in the transom assy itself... the scott clear hose test will tell you to check that one if there are bubbles!

just start at the water pickups and end at the exhaust... one piece at a time... so NOT fun :(

i'd much rather have no water than just barely enough water... least then you know it is REALLY broken! eek!

soooo much to check... the tip of the iceberg is barely visible... :rolleyes:

[MOP]

Does it have power steering? if so also check the oil cooler for debris, most the time you can back flush them and blow any junk out. Take the hose off from the drive, then use a garden hose blowing water back from the hose that attaches to the thermostat housing. Some over heats are tricky keep us posted.