Engine overheating.

[runner911]

Can anyone advise please ?

My fishing partner runs a Merry Fisher 925 fitted with a Volvo Penta D4 260, which now has 1600 hours running time on it.

The engine starts and runs faultlessly. It does not burn any oil and does not produce excessive smoke.

Towards the end of last season he noticed that the normal operating temperature of the engine had increased by around 5 degrees to 90 C.

Anything over 3500 RPM and the temperature shoots up to over 95 degrees which triggers the alarm.

The following work has been carried out to try to rectify the problem.

Heat exchanger removed and thoroughly descaled and cleaned.

Thermostat removed and engine run using a cleaner descaler for 4 hours.

New impeller fitted.

Full engine oil filter service etc.

Took the boat out yesterday. The engine now runs cooler by about 3 degrees but the problem has not been totally rectified.

Anyone any suggestions/ideas ?

Is a "cooler " running thermostat available for D4 engines ?

 

[superheat6k]

Starting from the seawater inlet ...

Coarse screen clear, Valve free and open, inlet strainer clear, was the pump impeller broken at all - if so have all the bits been found, oil cooler descaled - descaling the fresh water won't have touched this, after-cooler similar. Rydlyme is the best, but I find B&Q powder descaler works quite well. You need to work out how to 'pickle' the coolers, because the seawater system is straight through - drain the seawater and get the coolers filled with the descaler so it won't drain out.

Fresh water system fully vented, e.g. turbo vent (TAMD60 has this, not sure about D4).

Injection bend clear - often these get scaled up reducing flow through the whole system.

Then measure the seawater temp from the inlet to the point it enters the injection bend, preferably at sea under decent power. Measure the temp downstream of the injection bend - on my boat at WOT the exhaust after the injection doesn't rise above 43oC. If your discharge is running much warmer than this then something is slowing the seawater down.

My engines run steady at 85oC at WOT down to cruise. I do get a bit of steam following me which I regard as perfectly normal, as long as it isn't a fog bank. My exhausts exit just above the waterline.

 

[spannerman]

Starting from the seawater inlet ...

Coarse screen clear, Valve free and open, inlet strainer clear, was the pump impeller broken at all - if so have all the bits been found, oil cooler descaled - descaling the fresh water won't have touched this, after-cooler similar. Rydlyme is the best, but I find B&Q powder descaler works quite well. You need to work out how to 'pickle' the coolers, because the seawater system is straight through - drain the seawater and get the coolers filled with the descaler so it won't drain out.

Fresh water system fully vented, e.g. turbo vent (TAMD60 has this, not sure about D4).

Injection bend clear - often these get scaled up reducing flow through the whole system.

Then measure the seawater temp from the inlet to the point it enters the injection bend, preferably at sea under decent power. Measure the temp downstream of the injection bend - on my boat at WOT the exhaust after the injection doesn't rise above 43oC. If your discharge is running much warmer than this then something is slowing the seawater down.

My engines run steady at 85oC at WOT down to cruise. I do get a bit of steam following me which I regard as perfectly normal, as long as it isn't a fog bank. My exhausts exit just above the waterline.

All good advice, and don't forget the diesel fuel cooler just behind the diesel filter, and the charge air cooler above the starter motor, D4/6's have self bleeding turbo's so there will not be any air pockets in them.
If its an engine with a power steering pump, then another possibility is the servo oil cooler in the main seawater intake pipe just under the starter motor, have had overheating problems when these get blocked with weed, enough flow to run at mid range revs but not enough for full power, just like yours.

 

[julians]

I had a similar problem with my d4 260. Runs at normal 85 celcius if you keep revs below 3200, as soon as you go over 3200 the temp increases to 90 celcius plus, triggering an overheat alarm after a few minutes.

We removed and cleaned the following

Heat exchanger
Oil cooler
Intercooler

Found they were all clogged up to varying degrees. Now we sit at 85 celcius rock steady even at max revs.

It seems to be a common problem, but seems relatively straight forward to fix.

 

[Bandit]

You can descale seawater side of engine in the boat without dismantling using Rydlyme.

You pump it through for an hour with a little 12volt pump from a suitable inlet after the seawater impeller and out the flow before it goes in to the injection bend.

The injection bends do crud up after a while and that is a replace job, not that expensive .

Next time the boat is out of the water check if there is a slotted strainer grill over the seawater inlet, these get reduced by a build up of antifoul and barnacles so worth scraping out with a screw driver.