Overheating engine

[Squeaky]

Good evening:

Would appreciate some input on a question of overheating engine.

My neighbour has been complaining that his engine which was completely overhauled 40 or 50 hours ago is overheating and we have been trying to locate the problem.

We have removed and checked the neoprene raw water impellor which was ok. Tomorrow he will attack the heat exchanger to ensure that all the tubes are clear.

We have attempted to check the temperature gauge by measuring the resistance of the sender when hot and then applying the same sized resister to the gauge and the reading check out leading us to believe the temperature gauge is ok.

I have thought that he seemed to throw a lot of water against the quay when supposedly running at 800 rpm on the tachometre - personally to me it sounds much faster than that as that is my rpm in "tick over".

This afternoon I ran mine (29 ft - 23 HP) at 2000 rpm in gear while he ran his (32 ft - 30 HP) at 800 in gear and compared the amount of water thrown against the pontoon. I think his was pushing about 50 % more then mine leading me to believe that his tachometre was not correct or the propellor was much too big.

I am of the opinion that one can cause an engine to overheat simply by running it too fast - for example trying to make it exceed the hull speed etc.

My neighbour claims his engine will overheat at 800 rpm which if correct clearly indicates a problem but what if the tachometre is not correct and it is actually reving much faster trying to move an immovable object.

Would this not cause it to overheat????

By the way his exhaust seems to throw out more water through the exhaust then mine when running much faster.

Comments welcome.

Cheers

Squeaky

 

[Marsupial]

locate and remove the engine thermostate. test it to see if it works by putting it in a saucepan of water and heating it on a stove. it should open before the water boils. if it doesnt then buy another one.

 

[Liz_I]

Try testing the temperature sender.

We stripped our engine down only to find it wasn't overheating at all. The sender was telling porkies!

 

[branko]

!.Check and clean water filter
2 Clean heat exchanger
3. Check thermostat
Problem solved! /forums/images/graemlins/wink.gif

 

[silver-fox]

Squeaky

I think the first thing you have to do is identify where the problem lies by doing some detective work to isolate it, Hopefully the process below will help.

1. Is salt water circulating properly? Check exhaust to see if the expected amount of water is coming out. If not then check the following: -

a) Check inlet seacock fully open
b) Check inlet filter screen not clogged
c) Check output from water pump by disconnecting output pipe and running for a moment or two
d) Check outlet from heat exchanger using same method.

Typical problems you are looking for are: -

Blocked inlet ie polythene over the water intake
Blocked inlet filter
Failed raw water pump
Carboned up exit pipe from heatexchanger
Corroded/clogged up heat exchanger

2. If everything is OK and the raw water is flowing as it should then its time to look at the freshwater side.

Potential problems are

1. Water needs topping up
2. Loss of water via head gasket failure (check for milky engine oil emulsion, rough running of the engine. air bubbling through the water)
3 Fresh water pump failure - or maybe fan belt slack and slipping)
4. Thermostat may not be opening

A good check is to take the filler cap off run the engine and see what if you are getting turbulent water flow in the heat exchanger. If you are then you have water and you have water flow which narrows things down considerably.

As you run the engine the water should get hot fairly quickly, if it doesn't then suspect the thermostat. If it does get hot and you have already established that the salt water cooling is OK then suspect the heat exchanger is clogged.

Engines that overheat, when worked hard, are on their way to failure as the cooling system should cope with everything within the normal working load.

Hope this helps

 

[Squeaky]

Good evening:
Thanks for the comments however I guess I could have done better in framing my post if I had thought out the subject as my main aim was to determine what people thought about the engine overheating because of over reving the engine.

In my mind it is similiar to attempting to pull a heavy trailer up a steep hill behind a mini. I am sure that this will cause the engine to overheat if the transmission didn't blow up first.

As indicated we had done or were planning to do everything suggested. In fact today we opened the back of the heat exchanger and cleared all the tubes without any major change.

Tomorrow the elbow where the exiting water joins the exhaust pipe will be checked and the blades (metal) on the fresh water pump will be checked before taking the boat out for a run.

So far no significent change has been noted with the clean tubes but we are continuing to check.

At least my neighbour is learning his way around the engine in the meantime.

Cheers

Squeaky /forums/images/graemlins/smirk.gif

 

[grumpygit]

From what you are describing it sounds to be an engine fault for whatever reason. You are saying there is plenty water coming out the exhaust so the raw water side I would think is ok.

As others have advised try removing the thermostat but don't bother testing it, just replace the housing without the stat and try running it and see what results you get.

As far as the revs go I would think you should be able to judge whether it's over revving, it's quite a difference between 800 and 2000 revs. If the engine revs from a range of 800 (idle) to 2500/3000 (full throttle) I would say the tacho is reading the correct engine speed.

If all above seems to be ok the next thing to check is if the engine is pressurizing when it is showing hot. Be very careful checking this because you could get a face full of boiling water.
Let the engine get to its overheating stage, stop the engine and very carefully remove the pressure cap, preferably with a cloth between you and the cap. If there is not an excessive amount of pressure then I doubt the engine is over heating and it must be an instrument fault, (temp or tacho)

Anyway see how that goes and hope the above helps.

--------------------------------------------------------------

 

[Anonymous]

You've had loads of excellent advice and comment. I can only add that everyone should invest in an infra red thermometer (Maplins circa £20). Get used to checking the temperatures in the engine compartment (block, inlet water, fresh water outlet post stat, oil, header tank), and even the stern gland. Every few hours when motoring, when you do your greaser and engine checks, scan the engine. Oh, and do the batteries, too. You will pick up problems before they become an issue. One of the best bits of kit I have ever bought for the boat.

 

[grumpygit]

[ QUOTE ]
I can only add that everyone should invest in an infra red thermometer (Maplins circa £20). Get used to checking the temperatures in the engine compartment (block, inlet water, fresh water outlet post stat, oil, header tank), and even the stern gland. Every few hours when motoring, when you do your greaser and engine checks, scan the engine. Oh, and do the batteries, too. You will pick up problems before they become an issue. One of the best bits of kit I have ever bought for the boat.

[/ QUOTE ]

I agree with you as being a useful piece of kit but only if you know what you are looking for. In the wrong hands one could cause themselves a lot of flapping on no account. Useful in the help of diagnosis but not in prevention.

I've got this picture of someone looking into their bilges every 30 mins looking for problems. Nah ! /forums/images/graemlins/wink.gif

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[HenryB]

My engine overheated twice before I solved the problem. It was due to an airlock in the engine's water circulating pump. If your friends engine has just been rebuilt then this could well be the answer. I my case (Mercedes OM636 engine) it was due to a blocked pipe which leads from the pump - the sole purpose of this pipe is to stop airlocks.
Most engines have bleed points which should be loosened when being refilled to let any trapped air escape.

 

[Marsupial]

Squeaky, sorry but No, pulling anything shouldnt cause an engine to overheat. Engines over heat because the cooling system is faulty, either by design or wear and tear.

Furthermore it is not easy to over rev a diesel engine, unless you're descending a steep hill in a low gear -not the usual set of circumstances for a boat!

The more I read of this saga the more I believe the themostat is the trouble.

 

[TrevorSmith]

I’ll give you the benefit of my experience/ hindsight. I had a om636 that overheated. I tried everything. Just about everything that could have been renewed got renewed. No joy! After I re engined Westfield 4x4 told me the likely problem. Rust and other internal debris falls to the bottom of the block internal waterways. This blocks water flow and hence overheating. The way to clear is to take the engine out, remove the core plugs, flush jet wash whatever the waterways clear and then replace the core plugs. Unfortunately I found out this information after I re engined with a kubota 38hp. In hindsight I would have preferred to sort out the 636.

 

[Davy_S]

I would imagine they sorted it by now, as it was 13 years ago!

 

[Beneteau381]

locate and remove the engine thermostate. test it to see if it works by putting it in a saucepan of water and heating it on a stove. it should open before the water boils. if it doesnt then buy another one.

.

 

[Beneteau381]

Good evening:

Would appreciate some input on a question of overheating engine.

My neighbour has been complaining that his engine which was completely overhauled 40 or 50 hours ago is overheating and we have been trying to locate the problem.

We have removed and checked the neoprene raw water impellor which was ok. Tomorrow he will attack the heat exchanger to ensure that all the tubes are clear.

We have attempted to check the temperature gauge by measuring the resistance of the sender when hot and then applying the same sized resister to the gauge and the reading check out leading us to believe the temperature gauge is ok.

I have thought that he seemed to throw a lot of water against the quay when supposedly running at 800 rpm on the tachometre - personally to me it sounds much faster than that as that is my rpm in "tick over".

This afternoon I ran mine (29 ft - 23 HP) at 2000 rpm in gear while he ran his (32 ft - 30 HP) at 800 in gear and compared the amount of water thrown against the pontoon. I think his was pushing about 50 % more then mine leading me to believe that his tachometre was not correct or the propellor was much too big.

I am of the opinion that one can cause an engine to overheat simply by running it too fast - for example trying to make it exceed the hull speed etc.

My neighbour claims his engine will overheat at 800 rpm which if correct clearly indicates a problem but what if the tachometre is not correct and it is actually reving much faster trying to move an immovable object.

Would this not cause it to overheat????

By the way his exhaust seems to throw out more water through the exhaust then mine when running much faster.

Comments welcome.

Cheers

Squeaky

.