engine diagnosis

[snowleopard]

'my engine overheats if i do more than 4 knots' is all the clues i have though i do know that it's a fairly new engine.

once i've checked for impeller problems and blockages in the raw water circuit, what checks should i be making?

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[Talbot]

Thermostat broken in the closed position?
Air lock?


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[boatmike]

Is the engine properly aligned on its bearers? Does the engine reach peak revs easily when a) in gear b) out of gear? Does the propshaft freely rotate when disengaged? Is your overheating combined with smoke from the exhaust? Do you have the correct oil at the right levels in both engine and gearbox?

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[boatmike]

Good point! Check thermostat! (Take it out and boil it up in a saucepan to see if it opens)

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[gtmoore]

Definitely check the raw water inlet skin fitting. I've just helped a friend scrub his boat off who was having the same problem and the grating was virtually completely blocked with encrusted worm type fouling. I'm surprised his engine wasn't overheating at tickover!



<hr width=100% size=1><font color=blue>Gavin </font color=blue>

 

[brianrunyard]

Does it reach recommended max revs?
When you try to exceed 4 knots do you get black smoke?
If you can't get max revs and you get black smoke, you could be over prop'd causing the engine to labour.

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[Evadne]

Not just the skin, but the pipe too. Barnacle lavae are small enough to swim through any grating that may be fitted ... I found one when I closed then opened the gate valve (yes, I know,) and heard a crunching noise. Lots more cooling water after that one though.

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[snowleopard]

definitely not over-propped as this is a new problem.

i have raw-water cooled engines on snow leopard so not familiar with heat exchangers. what can i check on the fresh water side apart from coolant level?

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[Paragon]

Hi Chris

Given your mooring location, I'd be tempted to look at the heat exchangers themselves as they have become silted up so are working to some degree but not enough when over 4 knots (good fishing speed I recall!) Whilst I have not personally done it the unit (heat exchanger) should be removeable and some sort of end cap comes off to flush the thing through (just going on a piccy I've seen of another engine, not sure how your Yanmars are set up) I understand that this may even be an annual service job.

Anyway, that's my t'pennyworth!

Regards

John

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[steve28]

Is it actually overheating or is the sensor knackered ?

May be a swap with the other engine would prove this.

Thats my idea anyway.


steve

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[Nauti Fox]

Can you check the raw water strainer with the engine running?If there is an air gap at the top it may be as other posters have said fouled skin fittings.Got that on one of my engines at the moment.

<hr width=100% size=1>No dear,the water goes in the other one.

 

[snowleopard]

no john - the problem is on a friend's boat. mine is safely ashore now. hope to get more information about the motor sometime today.

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[oldharry]

If the engines are running normally otherwise - no smoke, starting etc, then almost certainly the problem is in the raw water cooling system. The fresh water cooler is like the one in the car - as long as there is water in it to the correct level and there are no leaks it will be OK.

The seawter side is another matter altogether, with all the mud, crud barnacles etc going through it, something has blocked somewhere: inlet fitting, strainer, pump impellor, heat exchanger can all clog up and cause overheating problems. I once had a hot running BMC, everything checked out fine - over and over again! Eventually we found a bit of rubbish had been drawn in and had stuck at the joint fitting of the outlet side of the pump. With the pipe disconnected there was ample water flow, connect it up and it reduced to a trickle - except you could no longer see it!

<hr width=100% size=1><P ID="edit"><FONT SIZE=-1>Edited by oldharry on 21/10/2004 13:34 (server time).</FONT></P>

 

[maxi]

Check out the raw water inlet pipe - these can delaminate internally and close themselves off whilst on-suction - similarly, if there is a bend in the pipe or any distortion, it is common for the pipe to be sucked flat as suction increases but appear normal with the engine stopped.
Try replacing the inlet pipe as a very cheap first step, or at least try a temporary replacement just to prove where the problem is, or isn't.,

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[silverseal]

Has anybody thought of looking at the raw water pump impellor to see if there is a problem with the impellor?

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[Keith]

I know it sounds stupid (but it happened to me) have you checked the v belt tension, my 2GM did the same and at low revs it was fine, at higher revs the belt would slip, after all they are weedy little belts, changing to toothed belts helps longevity.........keith

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[snowleopard]

stop press - more info

i've been in touch with the owner and got some more info-

the engine is an Alpha 40 (never heard of it, have you?)

it has a hydraulic drive and, wait for it, the raw water passes through the hydraulic oil cooler before the engine heat exchanger. in the past it has been ok up to about 5.5 knots but now overheats at 4 knots. the volume of water passing through the calorifier coils is good and the water in the calorifier gets v. hot. the heat exchanger has been checked and the flow is ok.

sounds like it's a raw water problem. a higher-lift cam has been fitted to the raw water pump in the hope of increasing the volume but limited success.

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[sailorman]

Re: stop press - more info

Lister/ petter engine
Lister made good engines
Petter ?????.

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[brianrunyard]

Sorry my mistake, I read "fairly new engine", as meaning you'd just reengined.

<hr width=100% size=1>Brian
http://homepage.ntlworld.com/brunyard

 

[anabel]

If you have tried all the very sensible suggestions mentioned so far you and still no joy , you might consider the soundproofing. A couple of years ago I had problem with engine overheating at high revs. The problem was the soundproofing. I had improved (!) this so much that the engine compartment was almost airproof. Consequently the air being drawn into the engine via the air-intake was getting hotter and hotter which inturn caused the engine to get hotter which in turn caused the temperature of the air being drawn in to get hotter and so on. Cured same by attaching exhaust type tube to air intake filter unit & leading it into the end of the quarter berth. This solved the problem.

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