Fluctuating engine temperature

[cliff]

[ QUOTE ]
Cliff,

Was it the Fernox DS40 you used ?
Here

Thanks
James

[/ QUOTE ]No, I used the DS3 - a full 4 KG of the stuff as there is some wastage due to spillage and steaming at the exhaust so I had to top up the bucket a few times and add more descaler. The concentration is given on the tub although I used a little stronger solution and remember as you are recirculating the coolant you can get a sea water cooled engine up to 90~95°C easily so the chemicals really work at the higher temperature. I have not used the DS40 on an engine - I think it may be a little fierce.
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo

 

[VicS]

I don't know how closely you have looked at the cooling system but the important thing to realise is that there is no forced flow of water through the cylinder blocks. In most (but not all) car engines the water pump discharges into the water ways of the block. The water then flows up to the head and exits to the radiator via the thermostat. In the MD series engines the water flows from the pump via passages in the exhaust manifold directly to the heads then around the heads exiting via further channels in the manifold to the thermostat. The cooling of the blocks is only achieved "by convection" through several (4 I think) smallish channels through the head gasket.
My theory is that once the flow becomes restricted in the blocks, at least through these connections between heads and blocks the water in the blocks boils ejecting steam and boiling water into the heads, the manifold and so to the temperature gauge sender (If I remember correctly that is behind the thermostat). Then fresh cool water enters and heats gradually until it boils again so repeating the cycle over and over again. It is only a theory.

We started with an engine that overheated, we replced the pump impellor checked the filter and the thermostat, of course, but eventually found the passages mentioned in the manifold were blocked, once we had cleared those we solved the overheating problem but then we noticed the flutuating temperature gauge. Somebody somewhere tipped us off about the probable cause of that so we then set about trying to rectify that the following winter. We tried a rather half hearted attempt to clean things chemically but eventually "bit the bullet" and took the blocks off. My friend, the owner, took them home and poked out the water ways as best he could, at least until he got a good flow from a hose in through the drains and out through all the holes at the top. It cured the fluctuating temperature.

(We found a broken oil feed to one of the rocker shafts during this so fixing that was on its own good enough reason for stripping down one cylinder)

Removing the heads is not a major problem but taking off the blocks is rather more difficult, at least the rebuiding is. It needs a particular type of piston ring clamp and you really should check the distance between the piston crowns and the top face of the blocks to ensure that the correct shims have been fitted between blocks and crankcase. If you can strip and rebuild a car engine then there should be no problems but if that is not one of your skills then perhaps this would be a job too far. Access to a workshop manual is, I would say, vital.

While you are thinking about the design of the cooling system think about the way you flush it out and fill with antifreeze for the winter. My guess is that most people run some fresh water through for a few minutes, but that only flushes out the pipework, and the heads if they keep going until the thermostat has been open for a while. Then they lob a couple of litres of antifreeze into the last gallon of water in the bucket and that whizzes through the by pass into the exhaust, a bit goes into the heads if they are lucky but virtually none gets into the blocks. Fortunately it is rarely cold enough and for long enough to freeze the salt water left in the blocks.
If the system is drained rusting will be more severe than if it is left full. As you will know air saturated water contains about 8mgO2 / litre or so but air contains about 256mgO2 /litre. Rusting will only proceed until all the O2 is consumed so a wet engine full of air will potentially rust 32 times more than one filled with air saturated water.

 

[PembrokeshirePromise]

Vic,

Thanks again for the comprehnsive answer - certainly sounds plausible. As the engine is currently running OK - I'm loathed to do anything in the short term thats too drastic (save that for winter !)

Stripping and cleaning the engine isn't something I relish - but would be happy to give it a go - I just do wonder how much cost would be incurred doing this - obviosuly head gaskets, seals etc - but my experience tends to suggest that once you start dismanting other bits will inevitably need replacing (as you found with your broken oil feed) - and then if I need to get anything machined etc etc.

When you say your friends engine overheated - was that a seize and stop type of overheat as opposed to just setting off an alarm ? Presumably once cooled it was OK again ?

Looks like my range of options are:
0) Remove gauge and carry on in blissful ignorance as before !
1) Check gauge a bit more thoroughly to see if it is charging fluctuation
2) Maybe fit an exhaust alarm to warn against any dramatic overheating
3) Flush through with boiler cleaner
4) Strip engine and clean channels - hoping to get a few more years out of it.
5) Cut my losses and look to replace this winter (new Beta drop in replacement - keeping sail drive -c. 4K, New Bukh - considerably more work to fit - and no option to retain sail drive apparently (sorry Cliff - I've seen your posts on tractor engines /forums/images/graemlins/wink.gif )- 7K + VAT)

When I factor in its other foibles (bit slow to start - though compression is apparently good - general condition in terms of the amount of rust it sheds - slight oil leaks - a bit smokey (though reliably told thats normal for an old volvo) I'm slightly loathed to spend too much effort / money on an engine that has to be in the twilight of its life ..

Of course what would be perfect would be total and catostrophic failure just as I motor upto the crane for winter lift out - at least it would be decided - but knowing my luck its more likely to be on craning in !

Thanks to everyone for advice and suggestions - at least I feel a bit better informed now. The good news is that at the present moment - it still goes - so isn't actually interfeering with sailing which is the main thing)

 

[VicS]

Overheating as in temperature gauge reading unacceptably high. For that reason don't disable the gauge just accept the fluctuations for now but be aware of its limitations.

The usual place for an alarm is in the exhaust after the water injection point (no we don't have one) that will warn of water low failure before the rubber and plastic bits get done for and also if you are lucky before the pump impeller wrecks itself. It won't warn of engine overheating though as there will still be adequate water flow through the bypass to cool the exhaust.

 

[pappaecho]

Forget the electrics. What is thet temperature uf the raw water after it leaves the engine - does it vary in temperature? If it does then you have some sort of cooling blockage. If the tempertaure of the water is warm to bearable hot, then throw away the electrics!
Remember that on the shuttle launch last week they had four sensors for fuel leaks - one read true and it was delayed, until they could find no leaks and decided to ignore it!

 

[PembrokeshirePromise]

Isn't the problme here that it can just be cooling water that has bypassed the engine block if the passages are furred up - and so is realtively cool - but still leaving the engine cooking.

But take your point about too many gadgets - put it this way - I can put my hand uder the exhaust outlet without discomfort - but then its come all teh way along the exhaust hose .... /forums/images/graemlins/confused.gif

 

[cliff]

Someone is pulling your plonker over the cost of a new Bukh. they are more expensive than the marinised tractor engines but not that much, HP for HP.

As for your problem I would try the obvious then go for a chemical flush running the engine to ensure adequate circulation if the descaling solution and give it time to work even up to 2 hours if needed seeing as Vic has described the crappy cooling system and the problem circulating through the block - what a sloppy design - you did say it was a Volvo didn't you? /forums/images/graemlins/grin.gif I rest my case your honour!
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillupo

 

[PembrokeshirePromise]

Thanks - reckon I will try the flush when I get a chance.

As for the engine price - came direct from Bukh UK - did say he might do a deal on the VAT though..

A large part of the difference was that the Beta can use my existing sail drive (110S) which whilst old in years appears to have virtually no wear on it (had it out last winter) and have a kit that will use the same mountings. Bukh appears to be starting again, new engine bay, mounts, sail drive the lot..

If the descaling works I'll put it all off for a while ....
You'll note that Volvo isn't on my potential shopping list /forums/images/graemlins/wink.gif

 

[cliff]

[ QUOTE ]
You'll note that Volvo isn't on my potential shopping list /forums/images/graemlins/wink.gif

[/ QUOTE ]Aah well, at least you are partially converted.
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“Artificial intelligence is no match for natural stupidity”
Skype id:cliffillup

 

[Birdseye]

You've got a lot of sensible advice here but let me add my bit. And that is not to do what most of us do and assume the most serious and expensive cause. Knock off the simple and cheap possibilities first.

After all, from what you say the only problem you currently have is funny numbers on a dial. Boat goes OK. Do you really need to do anything?

 

[paulsmith]

Had the same problem with a MD7B. It turned out to be blocked waterways in the exhaust manifold. its a simple job to remove the manifold, scrape/poke/fiddle the gunge out with bent wire etc and put it all back. Mine is now fine. Good luck
Paul