In real need some friendly advise

[gazza]

has your bmc got a bolt on water pump if so it could be your problem ie not pumping check belt is tight

 

the raw water pump belt does not need to be tight, it should be tight enough to drive the pump and that is it. if you did it as per an alternator belt you will wear out the shaft and pump housing in very short order.

 

 

the elysians BMC must have at least an inch of slack in the raw water pump belt.

 

 

 

the impeller should be in good condition though, 2 yearly replacement is a good idea.

Edited October 26, 2009 by gazza

[slowlane]

Can you explain further, please Robin ?

 

I have a standard BMC set-up with the 82 degree stat.

 

If the skin tank is adequate, the temperature really should never go significantly over that temperature, and in my experience doesn't, even if pushing on quite hard.

 

I can't see why "boiling" even with no anti-freeze, should occur below 100 degrees, and if the system is lightly pressurised, (usual cap is I think 7 psi), then even at 100 degrees, it shouldn't "boil", should it.

 

18 degrees (Celsius) seems a safe headroom to me, and since we got a bigger skin tank, adequately designed for the engine, I can't imagine why a stat over 80 degrees should be a source of worry. (Calcutt sell the 82 degree stats, after all).

Sorry to bother you again Alan!

 

they (the boat yard) told me that they had run her up hard for 2-3 hours on the dockside and never went over 80c, but when i took her out it overheated to 95c after 45 mins?,the same happend last weekend when it was ment to be fixed again they say they tested it and no overheating??.

 

how can that be?

 

If the engine is fitted with a calorifier, it should be taken from one of the ports on top of the engine at either end of the rocker box cover. The connection is usually a hose type spigot onto which the rubber hose is jubillee'd feeding the calorifier coil, there is no definitive answer to where it goes back?

A thermostat will help to heat up the calorifier quicker by passing all the hot water directly through the coil until the engine is up to temperature, then the thermostat will open and cool the engine (hopefully stopping it overheating).

It also helps by bringing the engine up to running temperature faster and thereby improving efficieny and/or fuel consumption?

The skin tank should be connected to the exhaust manifold (normally underneath at the front) and should return to the water pump which is on the front of the engine close by!

You say the system is unpressurised, so I am assuming there is a header tank of some sort without a pressure cap?

 

At your convenience you need to ensure:-

1) that the skin tank circuit is flowing freely. Do this by disconnecting the hose to the water pump and back flushing using the hose connected to the manifold. This should remove any sludge and sediment settled in the skin tank.

2) that the calorifier circuit is clear too. Find the return pipe and flush though by disconnecting the one connected to the top of the engine.

3) if you want a thermostat installed find one that is stamped at about 75C, anything over 80C and you will need to use a high concentration of 'antifreeze' to prevent boiling (I use that term as most people understand it, but the smae applies to 'summer coolant').

4) when the system is filled that you run the engine with the filler cap on the manifold removed until the air is expelled (there should be no more than about an inch between the water and the cap. Then you replace the cap and top up the system using the header tank.

5) after some time running you check the manifold cap again (you may have to put your hand over the header tank to stop it emptying) to ensure no more air has accumulated (usually from the calorifier circuit, but possibly from the skin tank).

 

Hopefully this will solve your overheating problems.

 

On the BMC/Hurth combination, it is usually necessary to remove the bellhousing in order to extract the gearbox, but this is usually a simple job unless there is very little space at the stern gland end or a complicated coupling is used.

Hurths can be a bit clunky, but should take up drive quickly. Check the oil (for ATF) and make sure its up to the mark, if it has another sort of oil in it, you will have to flush it/run it and flush it again to make sure the system is clean.

I don't see any point in worrying about failure as these gearboxs fail when they feel like it, so I would wait until you loose the drive and then exchange it!

 

Robin,

Robin,

 

May me sincerely thank you for taking the time to answer me in such detail, an amazing in depth reply!, you sound like a man who can!! Thank you so much!

[alan_fincher]

Sorry to bother you again Alan!

 

they (the boat yard) told me that they had run her up hard for 2-3 hours on the dockside and never went over 80c, but when i took her out it overheated to 95c after 45 mins?,the same happend last weekend when it was ment to be fixed again they say they tested it and no overheating??.

 

how can that be?

These things are notoriously hard to comment on remotely, particularly with not all the information.

 

Basically to my simplistic way of thinking, either you are running the engine up a lot harder than the boatyard is, or some other parameter is getting changed on the way.

 

I stand by my claim that a system that doesn't overheat if the thermostat is omitted should still not do so if the correct one is in place.

 

But if it's a wrong, or a faulty, thermostat, I don't understand why the yard cannot replicate it.

 

I suppose it makes sense to take it out, and see what happens then.

 

Are you able to....

 

1) Post a series of pictures of your whole set-up.

 

2) Fully describe your skin tank, (length, height, thickness, and whether it is known to have internal baffles in, or not.

 

Ideally a tank to correctly cool a BMC will be at least 6 feet long, full depth of boat's swim, "thin", (little more than 1"), and will have internal baffles to ensure the water can't bypass large areas of the cooling surface. Anything less may be "marginal".

 

I've got the Tee-shirt, but need to know more if I am to may halfway sensible suggestion.

 

If all else fails, can you not persuade someone from the yard to come out with you whilst you over-heat it. (Could turn into the dead parrot sketch, at weorse though, I suppose!)