Over-Heating Kubota Diesel

[snapdragon747]

Help, help, help!

I have a 2 cylinder Kubota diesel on my C&C 29

This overheated on my attempted crossing of the North Atlantic and resulted in my being becalmed on the George Bank for 6 weeks and then being hit by a hurricane on the Grand Banks. After that I was towed into Newfoundland.

Anyway, during my stay in Newfoundland I had the engine totally rebuilt. New pistons, rings, big ends, crank reground, rebored, new valves, new fuel injector pump, new injectors etc etc

On trials it was fine tied to the dock but over heated withing 5 minutes of leaving the dock. I put in a bigger heat exchanger, 3 times the size of the original! Still over heated. I by-passed the exhaust manifold and this has improved matters a little.

Now it is temperamental. sometimes it will o0ver heat after an hour, sometimes after two hours, sometimes after 3 hours. but it will always overheat at some point.

When it over heats its does so very quickly, fine one minute and 1/2 a minute later, whoosh up goes the gauge and it boils all the coolant out of itself. I then let it cool down and re fill the system via the top of the thermostat housing (themostat has been removed) It will be fine for 1,2 or 3 hours whatever.

Before strting th3e engine these days I always make sure the system is topped up via the thermostat housing.

The damn thing is fitted with an expansion tank with a new 7lb cap and a over flow bottle fitted below it.

Currently sitting here in Sydney Nova Scotia but we will be setting sail to halifax tomorrow or the next day and then onwards down to Florida. So if I don't answer immediately, then you know we are sailing from A to B


any ideas?


Thanks


george

[goboatingnow]

did you get the head re-skimmed, it could have warped.

[forsailbyowner]

Tried removing thermostat? Would run too cool but would seem to do less damage than overheating. Since it heats up so fast seems like something is obstructing coolant flow. Knew one guy who went through much anguish over cooling system. After doing everything possible including hiring a mechanic, he found a vane from a prior impeller blocking a passage.

[snapdragon747]

yes. The head was re skimmed. the whole thing engine was taken off to an engine rebuilding shop and returned fully rebuilt.
I think it may be an air lock but I don't know how to cure it

[cgaskell]

I had a hot water heater plumbed into the fresh water circuit and, although I have a remote tank that feeds the expansion tank from a higher point than the water heater, the circuit was air locked. I broke open the water heater hoses at the heater and the hose that fed the fresh water pump. I then manually filled the heater hoses, using a funnel and raising them as high as possible, until coolant leaked steadily from the break I made by the fresh water pump. Believe it of not, this worked... or at least it allowed me to run the engine at moderate rpms. If this is the problem, it would be much simpler for you if you have bleed screws on the expansion tank or water heater (if you have one). This theory of an airlock is feasible, although the fact that it recurs suggests that the coolant itself is boiling and creating airlocks while the engine is operating. Thus the quick overheating. Have you tried a more robust coolant?

[snapdragon747]

I haven't got a water heater on this boat,
I havew tried using 100% coolant of a good quality but it makes no difference

[cgaskell]

impeded cooling tubes in the main block?? were these cleaned when you did the rebuild? you could try something called penray off-line which is a two part cleaner for fresh water cooling systems. Available at truck stores, I think.

[Starbuck]

Sounds like a senile thermostat. Have you checked/replaced/removed that?

[Chief Engineer]

Never use antifreeze at 100%. It needs water in it to work properly.

Sounds like you have an impeller vane brken off in the hose near the water pump.

[Rex Delay]

Check your raw water intake hose. If not stiff enough, they can randomly collapse under suction causing such a fault.

[watersportgirl]

Is the same amount of water coming out the exhaust?

Sea strainer unblocked and working properly? (I knew of a fish getting sucked up past the strainer in one boat...yuck).

Was your heat exchanger new? Any leaks?

Muffler?

I'm curious (and totally a newbie) because I am looking at a rebuild myself.

[Chief Engineer]

Is this the type of cooling system with the thermostat mounted externally...recycling the water to the intake?

If so, look for obstructions anywhere

[osirissail]

- - Here are some ideas: As to raw water impellers - the little rubber vanes break off and sometimes lodge in the bends and curves of connecting hoses and pipes as the raw water makes the circuit from pump to heat exchanger to exhaust injection.
- - Restrictions in your raw water to exhaust injector. Closing off of the hole that allows the raw water to inject into the exhaust pipes "backs up " the system resulting in insufficient raw water flow over the heat exchanger.
- - If you have the wrong size water lift muffler it can create too much back pressure in the exhaust gas stream. In the same vein - blockages or too many restrictions down stream in the exhaust hoses that exit the boat can cause back pressure and overheating.
- - Over-propping the boat can also load the engine at low rpm's and cause overheating.
- - Use a handheld infrared thermometer to check the real temperatures at the various parts of the engine when it is "over-heating". It could be a faulty temperature guage (but from your description that seems unlikely) - however the infared thermometer can see if there is a specific part of the engine that is running extra hot which might help localize the source of the problem.
- - If you have a water-cooled exhaust manifold there might be a flow restriction happening there.
- - Speaking of fish in the sea strainer / raw water inlet - I had that a couple of years ago. Hired a diver to ream out the through-hull and then cleaned out the other end of the supply hose as best as possible and still insufficient water flow. I pressurized the hose end and out popped a perfectly dead 1.5" diameter fish. Close the seacock valve and take the strainer lid off. Open the seacock and there should be a serious fountain of water gushing into the boat. No serious fountain means something restricting the hose. Barnacles and other sea life love to grow inside the hoses restricting the flow. At idle or low power everything is fine but when cruising power is applied there isn't enough water coming through the hoses to keep the engine temp down.
- - I have both a port and starboard raw water system - the port side feeds the engine and the through-hull on the starboard side of the keel feeds the sea-water needs of sinks, air-conditioners, wash down pumps, genset, etc. I installed two tee's and a ball valve with a piece of hose to connect the port raw water intake to the starboard raw water intake. If I see the engine temp climbing I open the ball valve to allow the starboard side to also feed the engine. If the temp decreases then I know the port intake is clogged. But I can continue on using the starboard intake to keep the engine running.

[hpeer]

Believe it or not, I have had a similar problem with my Volvo MD7A - in Newfoundland.

The MD7A is salt water cooled. Water goes through the transmission, through a hard copper pipe, then to the impeller hosing on the engine. The connection at the transmission relied upon a copper compression washer. The engine had been removed and rebuilt just before I bought it and the "mechanic" created two problems.

1. He didn't replace the compression washer. He used some kind of goop. Once the problems started I didn't realize that the fitting took a compression washer and spent countless hours trying to refit the fitting before some old geezer fisherman set me straight. Once I got the right washer the seal sealed.

2. The "mechanic" didn't completely tighten the bolts holding the forward and mid transmission housings together sufficiently. After about 100 hours of running the transmission housings separated sufficiently for me to loose oil and forward gear. However, since the hard water line also connected the engine to the transmission that line must have been under stress and that was likely also causing the seal to fail.

I don't know which of these failure mechanisms caused my problems, or if both contributed. But in either case I would have gotten a small, intermittent air leak on the suction side of the impeller, which caused the overheating.

To be honest I have not run the engine a lot since finding these issues and it is possible that the problem will return. None-the-less I am 99% confident that at least one of these issues was responsible for the problem.

Good luck.

[SkiprJohn]

I always check to see if someone has added a larger prop. It'll make an engine overheat before reaching efficient rpm every time.
I think someone else said that already but its the first thing I check.
regards,