Overheating problem

[Sea_Lark]

I have an aged, fresh-water cooled Perkins 4108 that has started to overheat this season. It runs fine for an hour or so, but then the temperature gradually creeps up and up. If I then leave it to cool and top up with coolant, the cycle repeats, but some coolant has definitely been lost.

On one occasion, the engine ran for about 3 hours and was slightly below normal temperature all the time. I discovered later that in the early morning top-up of coolant I had left off the pressure cap from the heat exchanger. Incidentally, after motoring, but whilst still hot, the heat exchanger was brim full.

So, are then engine experts out there who can diagnose the cause of the overheating just from these observations. My gut feeling goes towards the head gasket, but please, someone, tell me its something much simpler.

A short-term solution would seem to be to fit a plain (non-pressurised) cap to the heat exchanger. Is this likely to cause further damage to the engine?

 

[TobyJug]

Hi,

Before suspecting the head gasket, can you confirm that the flow of raw water is as it should be . The jabsco impellor has all its vanes, the raw water strainer is clear, no kinked hoses and that the heat exchanger tubes are all clear and fairly clean.
Any or all of the above could give rise to the symptoms you describe.
The pressure cap is important as this elevates the boiling point of the coolant in the engine.

Hope this is helpful.

Seadog owner

 

[Sea_Lark]

Yes, all checked and the raw water flow rate is good.

I feared pressurisation was necessary, but any ideas why it runs cooler without?

 

[Avocet]

Might be worth repeating the experiment just to be sure. It sounds odd to be honest. Is it possible that the engine wasn't working quite as hard on the run without the cap? My only other thought (and a pretty tenuous one at that!) is that maybe with the cap off and the fluid level higher up, it was using a bit more surface area to exchange heat. Are there any tubes in the exchanger that aren't quite covered when the level is normal?

 

[Sea_Lark]

Actually the opposite. The engine was working harder than I usually run it when I left the cap off. I have once run it as hard with the cap on but still got overheating, of course. Not really worse than usual, though.

When topping up I always tend to overdo it and leave too little for expansion, so I lose some coolant anyway. This was true with the cap off and the coolant overflowed onto the heat exchanger, leaving a right mess.

With cap on, the overflow gets piped into the bilge, but I lose more coolant than just due to expansion. If I don't top up the engine overheats very quickly and excessively when next used.

The only rationale that I can come up with is that the coolant is over-pressurised by gas leaking into the coolant due to a faulty head gasket and then blows out the cap overflow taking some coolant with it. Then when I leave the cap off, the gas has a larger area to escape from and a vertical exit so doesn't take the coolant with it. But I'm not convinced by this theory!

Anyway, thanks for your musings.....

 

[chas]

My T90 was overheating and loosing cooling water earlier in the season. It took me a long time to trace the problem to a thermostat, newly installed, which did not have a breather hole in its rim. I drilled one and the problem dissapeared. I suspect that an air was trapped under the thermostat, and its sensor would not operate in an air pocket and therefore it did not open, causing the overheating and loss of cooling water. Might be worth having a close look at your thermostat.

 

[david_bagshaw]

there is a small chance the leak of coolant is in or at the end of the tube stack.

would suggest remving tube stack fromheader tank or whereever & checking the end seals /fixing method.

good luck

david