Can my engine overheat despite a good flow of cooling water?

[Geertje]

Having sorted out the fuel system of my 1955 40-plus (referred to in a recent post) and got it starting well on a 10:1 fuel mix, I now seem to have another problem.

When idling in a tank, and running gently in my dinghy, all seem fine and the motor runs smoothly (in a noisy, smoky sort of a way!). But after a time under load - such as against the tide - the running becomes less even, with occasional dips in revs, and what seems like a general dip in power. The last time this happened, the motor stopped suddenly altogether (at a rather awkward moment). And although restarted again a few minutes later then stopped almost immediately.

What I have observed is that the engine block become very hot under these conditions: not enough to burn the hand, but too hot to touch for long. However, the good flow of cooling water from the outlet on the underside of the block remains very cool - barely even warm.

So I'm wondering if its possible for the engine to overheat despite a good flow of cooling water - perhaps because of scaling or partial blockage - and if the symptoms are being caused by a resulting partial seizure. Is this likely or possible?

In the meanwhile, I'm trying some descaler inside the cooling passages to clean things out a bit, thinking this is at least unlikely to do any harm.

But what would others think/do in this situation?

James

[Mark]

I have wondered about that too.

I have looked at the FAQ, and there is a suggestion that the symptoms you describe could fit a faulty head gasket?

Just a thought. Look to see if there are any bubbles/smoke/steam coming from the head gasket after putting the engine under load.

[charlesp]

It may be a partial blockage. Sometimes muck and rust can build up and prevent a complete flow around the block, creating a hot spot. The only remedy is to take the block off, remove the head and have a thorough clean up of the waterways.

[CatiGull]

I will say your running symptoms identically match my posted experience of water in the petrol, so I would eliminate that as a cause before I tore into the motor!

[Charles UK]

You would expect the external water jacket part of the cylinder & the head to heat up for several minutes after the motor stops.
As with no water supply to cool the hot parts of the cylinder bore & cylinder head down, the temperature of the external parts would heat up far more than the normal running temperature as the heat is conducted away through metal to metal contact.

Give it a full service, that's points, plug lead, plug, complete fuel system & a compression test if it's none of those, your going to have to remove the flywheel it must be something under there.

You've got plenty of time to do that as it's almost winter in London & it will be too cold & miserable to use your boat.

[Geertje]

Thanks for all the helpful suggestions.

Just to clarify, the engine block is hot under running conditions - not after the engine is stopped.

Since my last post, I've had a chance to try my other new 40-Plus (1963) - and noticed that in comparison the block is cooler, and the water from the outlet is significantly warmer - which does seem to suggest that the 1955 engine is not cooling efficiently.

Just as I was feeling delighted with the functioning of the newer engine I noticed that previously good flow of cooling water had slowed to an intermittant dribble and then stopped altogether (at all throttle settings) . Quick inspection of the inlet failled to show any obvious blockage and as I couldn't restore cooling I ended up rowing home yet again.

So now I seem to have two engines with cooling problems! I'm really hoping some flushing will resolve the latest one. I've resolved myself that the first may need some more serious attention.

James

[RickUK]

Sounds like you've got to bite the bullet and take the cylinder heads off to descale the water jackets - it certainly seems the earlier engine is suffering from localised hot spots, which suggests that whilst water is able to make its way through the cylinder and out, an amount of the jacket is blocked. A healthy cylinder remains just warm to the touch under any running conditions.
You might get away with flushing or using a decaling solution as a temporary fix, but for long term peace of mind its a head-off job. Rick

[Mark]

I may have been lucky, but I have always managed to get water going again by using a high pressure hose put onto the water outlet.

[CatiGull]

I really like fresh water 'Gulling

[Geertje]

If I post much more on this topic it's going to start to resemble a Seagull-cooling blog.

But I'll just mention that I took the '55 engine - the one with good water flow, but overheating - out on the water again after soaking its insides in kettle descaler for a few days... and lo-and-behold it started to overheat again ... and then the waterflow stopped altogether! .But suddenly lumps of brown goo started to appear at the outlet and flow was restored! And subsequently it's been working really well with a noticably warmer water at the outlet, and the engine block significantly. I infer that a lump of rust or mud that was blocking one of the cooling passages became loosened and detached and now cooling is working more efficiently.

I've also restored cooling on the '63 by a bit of back-flushing and now this engine is working well too. It still feels quite strange to venture out in the dinghy and return without need for energency use of the oars.

Visitors to the Richmond area may notice the resulting increased levels of noise and smoke.

James

[bigoink]

One other point to remember..........If the oil mix in the fuel is too rich ,it will WEAKEN the mixture causing eventual overheating .