Running hot. 1973 Mercruiser 302

[Idodishez]

Bought a 73 Lund President w a 302 Mercruiser. Took it out for first time and in about 15 mins the temp gauge pegged. Shut it down and got towed back. Pulled the lower water pump impeller out and it was literally rubber dust, with a melted housing. I'm know for a fact the previous owner ran it without ear muffs hooked up. So I replaced the entire water pump kit. Reassembled and ran it with earmuffs to test. Water getting up to the motor now, confirmed by pulling a hose off at the t stat housing. It still got hot however. When it reached about 200 I shut it down. (Not sure if it would have gotten hotter).

Side note, the exhaust bellow on the stern drive is missing. Will this cause overheating issues for the lower unit? Does the lower unit get cooled by water/exhaust running through the unit then out the impeller?

I Pulled the UPPER water pump. No obvious damage to the impeller. Pulled t stat. No obvious damage but will likely replace just to be safe.

I noticed in the manual it says if the lower pump impeller is damaged, then the exhaust shutter valve in the exhaust elbow needs serviced as well. How factual is this? Would/could this be cause for it still running hot? Is this another 2 day project like the lower water pump was? (Could NOT get the driveshaft splines lined up. MAJOR PITA).

Assuming I don't have a gauge that's off, what else should I be looking at for the running hot condition?

Thanks

 

[Fishermark]

Re: Running hot. 1973 Mercruiser 302

Running it hot may well have damaged the exhaust shutter... but it shouldn't be the cause of it continuing to overheat. What was the last time you replaced the manifolds?

 

[Idodishez]

Re: Running hot. 1973 Mercruiser 302

I personally ave never replaced the manifolds. I've only had it a month or so. Why would you replace the manifolds as a maint item?

 

[Fishermark]

Re: Running hot. 1973 Mercruiser 302

Water runs through the manifolds and they can get clogged with rust and debris. This will affect the amount of water flowing through the engine and can thus cause an overheat. Being in Ohio you shouldn't be affected by salt water.... but since the boat is new to you it's hard to tell where it has been used in its life.

 

[Idodishez]

Re: Running hot. 1973 Mercruiser 302

Good to know. Thanks.

 

[cr2k]

Re: Running hot. 1973 Mercruiser 302

Power steering? Pull the water hose from the transom to the heat exchanger and clean out all the impeller pieces. Also check the thermostat housing. You are sure to need to replace the exhaust couplers (elbows to the Y pipe) as they have been toasted on the inside.

 

[Idodishez]

Re: Running hot. 1973 Mercruiser 302

No power steering. No heat exchanger, it's an open system.

Not sure I can explain it, but it ran today with no issues at all. I pulled the upper water pump and t stat as mentioned earlier. No issues found. I intended to replace the stat just to be safe. Couldn't find one locally on a Sunday. So put it all back together. Let it run at idle for 30 mins. Stayed at 140-160 degrees. Ok, I'll pump up the RPM. Let it run at about 2500 for 15 mins or so. Still no issue. Never got hot. All I can think off is me checking the stat and working it back and forth, freed up a previously stuck thermostat.

So next chance I get its off to the lake for a real world test.

That's for the input.