gradual overheating

[stuartwineberg]

Port engine on my Hardy 36 (semidisplacement) is overheating. Sabre Perkins 265. When I tootle along at 7 knots runs all day at around 82 degrees same as Starboard. When I wind her up a bit to around 10knots at 2100 revs the temperature creeps up over about 5 minutes to around 95 before I lose my nerve and slow down. Strainers clear, inlet not easy to ream out but a quick "flood test" with the top off the chests shows water coming into the strainer on both port and starboard sides at about the same rate. Ditto coming out of the exhausts on tick over. Water flow appears to increase signicantly out of the exhaust when I rev up in neutral. Impeller cover quite cold.

My thoughts - vane gone on impeller. Thermostat jamming. However a fairly well informed contact tells me that modern thermostats tends to fail open not shut and so wouldn't cause this problem.

Over to the wisdom of the forum. (BTW it is a pig of a job to get at the port impeller!)

 

[Latestarter1]

Port engine on my Hardy 36 (semidisplacement) is overheating. Sabre Perkins 265. When I tootle along at 7 knots runs all day at around 82 degrees same as Starboard. When I wind her up a bit to around 10knots at 2100 revs the temperature creeps up over about 5 minutes to around 95 before I lose my nerve and slow down. Strainers clear, inlet not easy to ream out but a quick "flood test" with the top off the chests shows water coming into the strainer on both port and starboard sides at about the same rate. Ditto coming out of the exhausts on tick over. Water flow appears to increase signicantly out of the exhaust when I rev up in neutral. Impeller cover quite cold.

My thoughts - vane gone on impeller. Thermostat jamming. However a fairly well informed contact tells me that modern thermostats tends to fail open not shut and so wouldn't cause this problem.

Over to the wisdom of the forum. (BTW it is a pig of a job to get at the port impeller!)

How often do you change impellers??

 

[Oscar24]

"Pig of a job to change port impeller" says it all.

Possibly never changed/checked?

Other item i would check would be the heat exchanger. My dad's engine was overheating recently and that turned out to be the heat exchanger being clogged up..

 

[volvopaul]

I changed them last year, as the water flow is good I'd say either there is a partial blockage in the outlet flow, or as the perkins has a gear driven freshwater pump it could be that the plastic impeller has broken off the shaft.

 

[stuartwineberg]

Impeller

Thanks for the reply Paul - hope you are well. When you say the plastic impeller may have broken off - do you mean the impeller itself or something relating to the impeller drive within the pump? If the impeller had broken off surely there would be no water flow at all??
Thanks
Stuart

Just noticed what you wrote - did you really mean the freshwater pump - how do I check that - I didnt know I had one - my attention has been completely on the seawater side

 

[Greg2]

Worth checking the actual temperature with one of those laser thermometers. I had a similar issue and found the engine temp was fine but the gauge was giving an incorrect reading.

 

[Latestarter1]

I changed them last year, as the water flow is good I'd say either there is a partial blockage in the outlet flow, or as the perkins has a gear driven freshwater pump it could be that the plastic impeller has broken off the shaft.

Well I never realised that! Certainly requires checking.

Old 6.354 cast irion volute was pressed on to shaft, Phaser base motor with gear driven circulating pump was plain nuts, however to use plastic volute on steel shaft even simply dumb. Many manufacturers have tried it and it ALWAYS ends in tears.....GM Bedord 330 for example plastic volute just ends up spinning on the shaft. More couch engineering.

 

[volvopaul]

Well I never realised that! Certainly requires checking.

Old 6.354 cast irion volute was pressed on to shaft, Phaser base motor with gear driven circulating pump was plain nuts, however to use plastic volute on steel shaft even simply dumb. Many manufacturers have tried it and it ALWAYS ends in tears.....GM Bedord 330 for example plastic volute just ends up spinning on the shaft. More couch engineering.

Yes nuts for sure but tams 61 and 71 has gear driven plastic vane pump, maybe driven into production by the same boffin!

 

[Assassin]

Thermostats can fail in any position but the spring closes them, it could be a sticking thermostat which is corroded and prevented from opening properly or fully.

 

[longjohnsilver]

Could be the heat exchange becoming furred up. Worth cleaning out, I've had good results with a product called rydlyme.

 

[PCUK]

As per Long John, heat exchanger tubes, oil cooler tubes (engine and gearbox), sea water inter-cooler tubes (if fitted). May not be as bad as this one, but if you've never checked!?!?!

 

[stuartwineberg]

Sounds like a potential issue

Yes nuts for sure but tams 61 and 71 has gear driven plastic vane pump, maybe driven into production by the same boffin!

On balance of the replies I think I am going to go:
Check mesh interceptor in the seawater feed from impeller to heat exchanger to see if it is blocked
Change impeller

Then either change thermostat (easy to access) or check freshwater impeller but where on the engine do I start undoing bolts to find this freshwater impeller. I guess not as easy to access as the seawater one

Thanks for the suggestions around blocked tube stack but the boat is only about 6 yrs old (approx 500 hours) and Paul checked those last year - all clear

Not sure if it would make a difference but I think I will have a look to see if there is anything round the prop

How does that sound?
Thanks
Stuart

 

[stuartwineberg]

Don't think this is it

Worth checking the actual temperature with one of those laser thermometers. I had a similar issue and found the engine temp was fine but the gauge was giving an incorrect reading.

Thanks Greg but the temp is so stable and so similar to the other engine when going slow and then so predictably goes up and down with speed I doubt it is this. if it was the sensor I think it would just read the "wrong" temperature all the time