Engine Coolant Problem

[meakinsl]

Was after some advice with an engine problem on a powerboat.

It is a friends boat and helped him drop it in couple of weeks ago and
we took it for a test run (bout 10 miles) and all was fine temp and oil
pressure wise.

Last night took it out for another run (flat calm), went five miles and
then anchored and then came back same route, when got to the lock it suddenly
overheated, killed the engine and discovered the radiator cap was loose.

What is strange is that cap hadn't been touched since it was serviced and
had been fine on the previous test run and until got back to the lock
last night. There was little coolant left but what is strange is no sign
that it had come out from the loose radiator cap as nothing over the block
or where the overflow is.

Was thinking that maybe a hose had gone and that maybe that contributed to
the cap coming loose or vice versa.

Someone suggested the intercooler might have dumped the coolant straight out
through the exhaust and that might be why no sign of coolant in the engine
bay - sounds a bit more expensive than a hose !

Be interested to get any throughts from people on what might be the cause,
unfortunately it was dark by time re-filled with coolant in the lock and got
it back the short distance to the berth so couldn't investigate further.

Many thanks for any help

Lawrence

 

[gjgm]

what engine is it?
What do you mean when you say there was a little coolant left? At all, or simply showing in the filler bottle?

 

[jfm]

Yep, need more precise info, and which exact engine is it? But the idea "the intercooler might have dumped the coolant straight out through the exhaust" is nonsense, so you can eliminate that one!

 

[meakinsl]

Apologies, thought after I had posted it that should have included more engine info. It is a friends boat so not entirely sure, the boat is 33ft and has a single large diesel 4 cylinder
engine. I think there is a salt water feed but not to the block but to a heat exchanger. There is then a separate cooling system with normal water and coolant which leads to an expansion tank. After the overheating which happened very quickly (< 1minute at end of 5 mile run) there didn't seem to be any coolant left. We re-filled it with about 7 litres of fresh water mixed with coolant and then ran it back to the berth.
Was pitch black when got back and couldn't spend any longer on the boat so not sure if it lost any more coolant on the short run from lock to berth. What was strange on neither the block nor the expansion tank was there any sign of coolant having leaked from those sources.

Regards,

Lawrence

 

[gjgm]

well some of the Volvo's should have virtually no water in the reserve bottle, as the expansion is such that if you top it up (even to MIN level) it ends up all over the bilge.
So I m not sure that IF your observation was that the bottle seemed low, that means anything much.
Still 7 litres does sound alot of top up. That does sort of suggest some leakage.
No sign of any green liquid anywhere about the engine or bilge at alll? Cant see how you can have lost coolant OUT of the boat, to be honest?

 

[carlton]

[ QUOTE ]

Still 7 litres does sound alot of top up. That does sort of suggest some leakage.
No sign of any green liquid anywhere about the engine or bilge at alll? Cant see how you can have lost coolant OUT of the boat, to be honest?

[/ QUOTE ]

Cylinder head gasket ?

 

[MikeL99]

I can answer some of the above questions as it is my boat we are talking about. (thanks Loz for starting this thread).

The engine is a Yanmar 4LHa STZP with a Bravo 3 leg. It has a closed loop cooling system which is cooled via a raw water heat exchanger pulling water in through the Bravo 3.

The temp had been fine for the run back to the marina and dropped off as we slowed to 4knts on the approach to the lock (all perfectly normal). the temp suddenly rose as we were tying up to the pontoon in the lock and on inspection the only problem we could find was a lack of water, but with no sign of coolant in the bilge or over the engine itself.

I spoke to the engineer who serviced the boat this morning and he thought it might be possible for the water to have escaped out through the exhaust if there was a leek in the intercooler, but he did add the caveat that he would need to check the schematics of the cooling system to see if that was possible.

Thanks in advance for any advice.

Mike

 

[MikeL99]

Head Gasket did cross my mind but have not had a chance to check the oil yet as it was dark when we finally got back to the berth. If it was the head gasket i would expect it to have been a more gradual loss of coolant.

Just to confirm the engine has a small expansion bottle which had no water in and the 7 litres went straight into the engine (not the expansion bottle).

 

[gjgm]

ok, we dont know the coolant level before..we are just assuming it has lost alot.
Might be the case, but it might just be worth running it up again to check it wasnt a plastic bag over the intake, or it isnt a slipping belt- or whetehr it loses more coolant.

 

[Firefly625]

[ QUOTE ]
but it might just be worth running it up again to check it wasn't a plastic bag over the intake, or it isnt a slipping belt- or whether it loses more coolant.

[/ QUOTE ]

Sensible idea. But first check oil, if it resembles cream of mushroom soup then it probably points to head gasket. BTW, for no other reason but being nosy, where are you based?

 

[MikeL99]

Unfortunately I did not do an engine bay check before we left (which I'm now regretting) but the fact that the boat ran perfectly at 25 knots for some time and then overheated on tickover suggests to me that it is either a sudden loss of coolant or a blocked raw water intake.
We checked for bags but did not find any. I also checked the belts as I have had one snap in the past which caused the engine to overheat so I am painfully aware of that problem.

I'm heading down after work to check the oil and maybe run it up to check for leeks so will let you know.

I'm based in Swansea which is a great place for boating when the weather is nice...

Cheers
Mike

 

[gjgm]

wont explain loss of coolant, but might as well check the impeller too.

 

[Firefly625]

good luck, on the basis it was OK at 25knts and overheated on tickover may well suggest blocked strainer. /forums/images/graemlins/smile.gif

 

[davedpc]

Once had water into oil via a gasket. As oil pres. is usually higher than water pressure this only happened on tick over. At higher revs. oil went into the cooling which was forced out through the fault. Check your oil level.

 

[[2068]]

Engine oil level going down for no apparent reason = bad
Engine oil level going up for no apparent reason = very bad

 

[scubaman]

Some volvos (Kamd-series) are prone to loosing coolant through the filler cap as it doubles as a overpressure relief, i believe. This may happen gradually without leaving much of a trace to be seen. I don't know if this is possible in yanmars.

When you check the oil, have a good look around the outside of the block to check for leak stains. Again talking about volvos, a leaking head gasket may also leak to the outside of the block, so your oil would be fine, but you'd be loosing coolant which would evaporate from the side of the hot block before reaching the bilges.

The coolant may have been lost gradually and eg. Coupled to some debris blocking the intake, the overheating occured.

Interesting though, please keep us posted.

 

[gjgm]

being ignorant, what causes pressure to go up ?

 

[[2068]]

oil level, not pressure

going up = contamination, either from water (=mayonnaise) or diesel

 

[Elessar]

Had to be Wales with a leek in your engine......