Overheating engine

[RosieP]

Hi there,

I would like some advice on what I think is an overheating engine. The engine is a keel cooled Mitsubishi 414.

We stopped after about 10 minutes cruising because of steam coming from the engine. This was about a week after doing an 8 hour cruise with no problems at all. We found that one of the water pipes (not sure if its inlet or outlet – the bottom one into the thermostat housing) from the thermostat housing had broken (cause unknown). We made a temporary fix with some hosing and went on our way again after topping up the water in the engine. The engine then cut out due to over heating with steam coming out of the water-cap. At this point our domestic hot water tank was not being heated via the engine any more (whereas there had been no problems with this before). After repeated stopping and starting we pulled up for the night.

The next day we tried taking the thermostat out in case that was causing problems but the engine still seemed to be getting very hot and it was still the case that no hot water was making it through to heat the domestic hot water tank.

Possibly unrelated and possibly not the belt which turns to make electricity also snapped at some point.

Also possibly unrelated the engine had just been serviced!

Please help!

[SamKingfisher]

Hi. Sounds like you have an airlock in the cooling system. You will need to bleed it, possibly by loosening hoses until water flows from the joints, then re tightening. The alternator belt isn't relevant to the overheating I wouldn't think. Possibly the servicing of the engine disturbed a hose, which then split. Others with more knowledge will be along shortly.

[Alan de Enfield]

One of the reasons for 'boiling up' was the fan-belt snapping.

 

Not only does this belt turn the alternator to produce electrickery, it normally turns the water pump to cool the engine.

 

The fact that the calorifier (hot water tank) is cold is probably that when the water boiled out of the engine, and you refilled it, there was an air-lock (air bubble in the system) that stopped the water getting to the calorifier.

 

Without wishing to be rude, I think that with the level of understanding shown in your questions it would be better for you to get an engineer out to look at, and resolve the problems - alternatively if you ask, and say where you are then someone may offer to help.

Edited September 14, 2014 by Alan de Enfield

[Captain Fizz]

Where are you RosieP?

[bottle]

Almost certainly an air lock.

 

Try running the engine (whilst moored) with the thermostat refitted but with the filler cap off.

 

Make sure the header tank does not run dry

 

Now be careful because you may get boiling water splashing out of this hole.

 

No guarantees but it may just work.

 

If it doesn't then bleeding of the systems is required and there may be bleed valves to do this.

[RosieP]

Thanks very much all.

 

That makes much more sense now. Can I just ask: if the belt came off, would that have caused the overheating by stopping the water in the cooling tank circulating? If so, is there necessarily an airlock there at all? Or could the absence of the belt be the sole cause of the problem?

 

I'm in central London at the min, so it hopefully won't be too much trouble to find someone. If it is just a case of replacing a belt,and bleeding the tank, though, is that something I'd need to call someone out for? Is the engine repeatedly overheating likely to have caused further problems I don't know about?

 

Thanks again for the help....

[MyLady]

If you have a subscription to RCR, call them. You may not get a final solution within their time limit, but you should get a temporary fix and a first estimate of the problem from a qualified engineer, all for free.

 

If not, then sign up ready for next time, IMHO novice boaters need RCR just as much as novice motorists need the AA or RAC. (BY 'novice' I mean anyone who knows too little to strip down and reassemble the boat/car systems that make it go and stop.)

 

Just my two-pennorth, for what that's worth, probably just a hapeny! (Meaning 2d & 1/2d respectively...)

 

Roger

Edited September 14, 2014 by MyLady

[MtB]

Thanks very much all.

 

That makes much more sense now. Can I just ask: if the belt came off, would that have caused the overheating by stopping the water in the cooling tank circulating? If so, is there necessarily an airlock there at all? Or could the absence of the belt be the sole cause of the problem?

Absolutely YES. The vee belt breaking or falling off would immediately cause overheating as the circulation of cooling water through the skin tank would stop. The engine would then boil away the cooling water. I very much doubt the preceding posts suggesting an air lock if the belt is still missing. The boiling of the engine could easily have caused that hose to burst too.

 

I'm in central London at the min, so it hopefully won't be too much trouble to find someone. If it is just a case of replacing a belt,and bleeding the tank, though, is that something I'd need to call someone out for? Is the engine repeatedly overheating likely to have caused further problems I don't know about?

 

Thanks again for the help....

Yes. Fit a new belt and fill with water and as likely as not, all the problems will vanish. get a new engine hose though...

 

 

MtB

[bottle]

Do not run the engine without the belt being replaced.

 

Edit: Mikes is the much better explanation

Edited September 14, 2014 by bottle

[MtB]

P.S. Once you've got the engine running at the right temp again, remove some water and add the correct type and concentration of anti-freeze

[matty40s]

Yes it would Rosie, your engine needs the belt to run your water pump. No belt means no water circulation.

 

The top hose was replaced following the rusted thermostat removal.

I am not sure I replaced the bottom hose or not.

There is a bleed valve on the top of the skin tank, there may be some air in this if you have overheated, loosen until the liquid appears then retighten.

Then loosen the top hose from the thermo housing until liquid appears, then retighten.

I can probably talk you through this if you want to give it a go as I remember the engine bay vividly!!!

Edited September 14, 2014 by matty40s

[RosieP]

.... hopefully a crisis averted, then.... Great explanations Mike and Bottle

 

I'm afraid I did run the engine quite a bit (maybe a whole day) - hope it hasn't done too much damage.

 

Thanks Matty - I'll give you a ring if we've more problems. Surprisingly, this is the first one we've had since this time last year...

[MtB]

I'm afraid I did run the engine quite a bit (maybe a whole day) - hope it hasn't done too much damage.

 

Oh dear, in that case there is every chance you have totally wrecked it. Were there no warning lights or buzzers?

 

MtB

[RosieP]

Oh dear - would there be any further signs if I have wrecked it? It still starts fine and there were no warning lights or buzzers at all.

 

It seems it probably is time to get a proffesional out,

 

Thanks again...

[bizzard]

Oh dear - would there be any further signs if I have wrecked it? It still starts fine and there were no warning lights or buzzers at all.

 

It seems it probably is time to get a proffesional out,

 

Thanks again...

Engine cylinder heads, especially diesels don't like being starved of water, they can crack and warp. However its probably ok. Do what's already been said. Let air out of the skin tank, fill system with coolant, squeeze hoses to help air to escape. Start the engine with the water filler cap off. Keep a keen eye on the water level. Blip the throttle up and down, if the water level rises and and falls by a large amount or keeps overflowing its riding on trapped air. Get the engine up to running temp topping up the coolant as needed. Keep revving the engine up and down, you should see bubbles of air escaping at the filler. Keep on and on doing this and topping up until all the air has escaped and there is no sign of air bubbles or fizzing streams of bubbles in the header tank and the water level remains steady with only a little change in level as the engines revved up and down. If no more air, top up and replace the cap and check the water level regularly.

If after a long period of this treatment the air bubbles escaping are still very evident then it would be best to call in a mechanic to check it out.

Be aware of hot water bubbling out of the filler and scalding you.