Engine Overheating --- 25 HP 3 Cylinder Diesel

[Mike ROAM]

VETUS M3.09 25HP 3 CYLINDER aprox 5 years old 620 Hours

OVERHEATING.

The engine will run happily all day at around 1500 RPM but ... once the revs are increased

it will overheat in a matter of minutes triggering the warning light buzzer at aprox. 90

Centigrade and the temperature will continue to climb.

Plenty of water comes out the exhaust which is not at all hot. The exhaust elbow does not

get hot.

There appears to be NO problem with the raw water system.

I have performed the following WITHOUT improving the situation.

The tempreture sensor was placed in a kettle and boiled. The temperature guage showed

aprox 100 centigrade as it should have.

The engine has been run without the thermostat and still overheats.

* Replaced the Raw Water Imepllor.

* Opened both heat exchanger end caps and cleaned through each individual tube

thoroughly. ( Some were very clogged and I thought I had found the problem... again it

made no difference ).

* Replaced oil and Filter ( at it was on the overheating Troubleshooting List ).

* Checked V Belt Tension.

* Made a visual check of the Coolant pump ( usually it is the baring that goes on the

pumps and they become a little wobbly ..it appears fine.

* The coolant pump appears to pump well.. engine was run at idle speed with the

thermostat housing open with thermostat removed watter was pumped into the housing

and flowed over the top.

* I have removed the coolant pump intake ( pipe below the pump ) and blown hard on

it.. water seems tocirculate well as it begins to pour out through the top of the

thermostat housing which would indicate that there are no blockages.

* I have removed the exhaust and the exhaust elbow to look for excessive carbon build

up. It was only slight and removing it and replacing it made no difference.

Observations:

When I look into the top of the heater exchanger .. which is also where one fills the

coolant ... it appears that there is hardly any movement of the water .. it really only looks

like the only movement is from the vibration of the engine.

There is no oil in the coolant and there is no coolant in the engine oil.

Any help woule be greatly appreciated...
Thank you, Mike

 

[caiman]

Hi
Nobody has replied to your thread so here's my bit.
The symptoms describe indicate to me either the boss of the sea water impellor is spinning within the blades under load(ruled out by exhaust elbow cool and replacement impeller),or the thermostat is not opening properly(ruled out by removing the thermostat).
Have you checked the fresh, engine side, water flow into and out of the heat exchanger?Maybe there is a partial blockage between the thermostat housing and the heat exchanger outlet?That may account for only seeing vibration movement on the water?
Good luck.
Cheers.

 

[RogerMayne]

Hi, you seem to have covered the main possibilities. The only thing I can think of is that you may have a very small crack in the head, block or liner which is allowing hot gas into the coolant above a certain revs. Try filling with water, leave the pressure cap off and run it up and see if the coolant becomes pressurized as you increase revs.

 

[yoda]

Your own observation of the lack of flow on the freshwater side of the heat exchanger would to me be the first thing to look at. You say that the engine is no better without the thermostat so either the freshwater pump is not working ot there is a blockage. Only other thing that could possibly be a problem is an airlock in the freshwater side.

yoda

 

[Bilgediver]

Hi, you seem to have covered the main possibilities. The only thing I can think of is that you may have a very small crack in the head, block or liner which is allowing hot gas into the coolant above a certain revs. Try filling with water, leave the pressure cap off and run it up and see if the coolant becomes pressurized as you increase revs.

It seems your sea water side is fine as lots of water circulating,
I would suggest th touch process. Feel around the engine and the heat exchanger fresh water side to see if you can identify how hot the water is in different parts of the circuit.

You cleaned out the sea water side of the heat exchanger however you do not appear to have inspected or cleaned the fresh water side and this is where the problem might be.

 

[charles_reed]

Either the heat-exchanger has still got a blockage or, very unusually, the freshwater coolant pump, usually inside the head, needs attention.

If the latter, the coolant will still circulate due to thermo-siphon effect, but the flow will be insufficient when the engine is working.

 

[yoda]

Link below may be some help in case you don't already have it.

http://www.vetusweb.com/manuals/files/Vetus_M-Series/340102.04 r02 01-08 M2_M3 EN.pdf

Yoda

 

[bendyone]

Have you removed the heat exchanger stack and cleaned the outside of the tubes?

 

[eagleswing]

engine overheat -pressure test, & more things to check..

here is what i've done to trace a pesky cooling system antifreeze leak:

1) clean the engine compartment, all hoses associated with t he freshwater system and thebilge, dry them . you want t here to be NO antifreeze drips anywhere before you start the test. put a few white rags under the engine in the bilge so you can see an antifreeze drip. fill your radiator and overflow tanks with antifreeze to proper levels. if you suspect a hose or gasket leak, put a white paper towel, held on with duct tape, so you can track any drip, seep or leak. figure out where your f \reshwater pump is that pumps the antifreeze and clean its bottom 'seal' or weep hole area so you can check for leaks 'later..' in the pressure test

2) get a pressure tester from an auto part store and replace the engine radiator cap with the pressure tester. pressurize the radiator system to 15 psi and watch for telltale drips or antifreeze on any of your towels or rags. DONT move the towel or rag, the position of t he drip will alert you to which component is likely the source of the leak. IMHO it is safer to test for leaks this way than to run the engine .

3) take some pictures of the drips so you can run those by a mechanic...

in my case, a recent cooling system flush and sloppy reinstall of the coolant drain plugs resulted in a cross threaded drain plug . the plug was not sealing , and that was allowing antifreeze to flow out at the drain location... which i found by the tell tale marks on the towel right under the offending drain plug..

if you can't force the system to leak when under 15 PSI by the pressure tester, write back --as there are some more things to try...

good luck..