Subject: Saab marinized Mitsubishi coolant thermostat 


Hello, I have a kd4 Mitsubishi that was marinized by Saab engine and its reliable but parts seem non existent for it here in the USA. Was wondering if you knew of a parts supplier in Europe that I could order from on line.

I need a spare thermostat for safety and can't find one here in the USA. I have tried to order direct from the factory in Norway but they are reluctant.

Thank you for your time

Rich Jamsen

I have a boat with twin Volvo KAMD42 engines and one is over-heating.

It runs all day at low speed cool as I increase throttle it increases in temperature. Its max revs are 3800 as I get to 3000rpm this is as far as I can go to within its max working range BUT I cruise at 3300 rpm to get best speed and if I put the revs up to that I go past 210 degrees and keeps on climbing?

I know there is a good supply of RAW water ...you can see it plowing out of the exhaust. So that must leave the problem with the fresh water system?

I am going to assume the tube stacks in the heat exchanger are blocked or the thermostat is not fully opening or stuck. I can tell you that 12 months ago a belt snapped and the pump stopped, then she overheated and Bang she boiled and the exhaust gasket blew. I wonder if that excess heat on that day has affected the thermostat or caused the tubes in the exchanger to clog up?

What do you think?

One more question ( as Columbo says ) Where the hell is the Thermostat on my engine a KAMD42?

Thanks,

Paul

ANSWER

Dear Paul

I do not know exactly where the thermostat is on your engine, but it will be under a housing, close to the top of the engine, where a largish hose connects the cylinder head to the heat exchanger (which may well be inside the exhaust manifold).

I would expect the housing to be held down by two or three nuts or bolts and a new gasket is often required.

The overheating may well have damaged the thermostat, so that must be the first thing to replace, but if that does not solve the problem I think that the overheating has damaged the cylinder head gasket. This is far more likely that blocked heat exchanger tubes if you still have lots of water coming from the exhaust (blocked tubes reduce this).

The symptoms are classic for head gasket failure, but any sever overheat may force the wax out of the thermostat causing late or even not opening at all.

 

Tony Brooks

Hi Tony

I have a similar overheating problem to others published. I have a 60'narrowboat built in 2003 by Braidbar Boats with a Beta 1903 1.8 engine, keel cooled. At 1800 revs the temp is a steady 100C, but any higher revs pushes the temp up towards the danger level. Any prop fouling causes engine overheating rapidly. I recently had to punch the tide on the upper Warwickshire Avon, maximum revs being required. The engine overheated and the alarm buzzer activated - (this was scary in a cloudburst with the river in spate and absolutely nowhere to moor!).

It would seem that the keel-cooling tank is of insufficient size. I note your suggestion to add cooling pipes to the opposite swim, but this seems drastic and I am sure I would be forever concerned that debris or whatever would damage the pipes. Is it not possible to replace the existing tank with a larger one?

I have read that there is a possibility that air is trapped in the cooling tank, but I can't find any instructions anywhere on how to bleed the tank (I am inexperienced in marine engines and their cooling systems). There is a bleed valve on top of the tank, and I assume that this is used, but do I bleed it with the engine running?

It is understatement to say that I am peeved to find that my £80k vessel cannot safely be taken onto a river, and on a canal overheats with the slightest fouling of the prop.

I am surprised to find that the boat builders are able to install an inadequate tank - I would have thought that the safety element applies here- after all it extremely dangerous for a vessel to have an intrinsic design fault which can cripple the engine. I do have an engine test certificate signed when the boat was new, but I assume that this testing was carried-out when the boat was 'clean' and the keel cooling at its' optimum performance.

Any advice will be greatly appreciated.

Kind Regards

Ted K

ANSWER

Dear Ted,

The bleeding should be easy.

Ensure that the coolant level in the filler is higher than the skin tank, then simply loosen the bleed screw. When it stops hissing and bubbling with only coolant coming out of it (no air) do it up again.

Top the engine up as required with a 50% antifreeze mixture.

You should also be able to bleed it with the engine running, but I would wait until it reaches normal operating temperature to ensure the thermostat had opened. In this case take care to avoid being scalded by hot water and steam.

To do a rough check on skin tank area expect half a sq. ft. per horse power for about 65% of the engines rated power. I expect this will work out at something like 12 sq ft.

I do not recall which reply you are referring to, but in your case rather than fit simple pipes on the other swim I would advise a new tank on the outside of the swim once all other possibilities are ruled out (because of expense). Look up back copies of Canal Boat because they did a feature on this about a year or more ago.

There is no merit in having a thick (higher capacity) skin tank, you need a thin one to maximise the amount of cooling water in contact with the hull. The tank should also be baffled. Also note (ready for the inevitable arguments) that the thermostat will prevent "over cooling", the larger the skin-tank area the better.

Ensure the outer side of the hull that forms part of the tank only has two or three coats of blacking and not the build up of years. It is not likely, but ensure that the belt that drives the engine water pump is at the correct tension (about 1/2" deflection at the centre of the longest run).

You also need to ensure that your thermostat is correct for marine use and that the head gasket has not failed. Boiling can make modern thermostat fail, so a replacement would be a good idea.

You are in a bit of a cleft stick here because your builder is not known for cutting corners, so one always has engine faults like internal cracks or porosity at the back of ones mind.

It is the propensity of the "trade" to make mistake after mistake that prompted me to offer this service. I to am appalled at the standards (or lack of them) displayed by so many in the trade.

I hope this helps

Tony Brooks

i have a boat with a 212hp Mermaid all the normal things have been done all the raw water system has been doubled checked as has the raw water side but over 1800 it gets hot, I need a "new" pair of eyes to give it a kick, any ideas

Chris

ANSWER

Dear Chris

Have you checked the exhaust pipe and mixing elbow for blockages, delaminating etc. Any exhaust blockage will cause exhaust pressure to rise against the raw water pump as speed is increased. This reduces raw water flow and hence causes overheating.

If you have ensured any oil cooler tubes, the heat exchanger tubes, the raw water hoses are clear and in good condition and also that the raw water pump is not badly worn, has a good impeller and the correct gasket, we are left with an engine/secondary water problem. (I assume the sea inlet cap and associated suction hoses are vacuum tight!)

If the thermostat is ok, then I start to fear head gasket or internal cracks/porous castings, but unless you have suffered a "boiling" overheat episode these are not likely.

I hope this helps

Tony Brooks