Engine overheating - help please!

[Guest]

Hello all - can you help with this

Volvo MD5A (9.5hp deisel 1980). Working like a dream until 2 days ago. The temperature warning buzzer (but not the warning light!) comes on after 25 mins from starting from cold, and after 10 mins when started warm (ish). I am a complete bozo when it comes to engines. Can anyone give me some pointers as to the likely fault(s) and, if possible, the cure(s).

Any comments gratefully received

 

[hlb]

Make sure youve opened the sea cocks for a start. Then check the water strainers. Fit a new impelor cos if it was not knackered before it will be now. Report back when these are checked to look deaper into problem.

No one can force me to come here-----------
----- I'm a Volunteer!!!

Haydn

 

[oldharry]

The overheat warning coming on means there is little or no cooling water circulating. Blocked seawater inlet (there should be some form of a strainer) is the most common cause, caused by seaweed, poly bag or some other rubbish being sucked in.

If thats clear check the pump impellor which may be damaged or have collapsed. If you do not know how to do this, get someone to show you now It could save your boat and maybe your life as well next time, and is essential safety knowledge.

After that it gets more complicated, and if you don't know what your doing, you will probably need an engineer as you will be looking for failed thermostat, faulty alarm, blocked exhaust, or some other engine fault causing the overheating.

DONT go on running the engine when the alarm goes off, except to save the boat. An overheated engine can make a VERY big hole in your bank account, and could possibly cause an engine room fire.

 

[webcraft]

Had a problem with a Volvo MD6A overheating the weekend before last on the way up the Sound of Mull.

Turned out the hose from the seawater inlet to the impellor was too long, resulting in it kinking when the companionway steps were replaced.

Shortened the hose with a sharp knife - no further problems.

- Nick

BlueMoment.Com
http://www.bluemoment.com

 

[Guest]

Thanks for the comments so far - I should have said that there is a healthy flow of water out of the exhaust. I am thinking it may be a knackered thermostat or a blockage in the circulation of some part of the engine. Is it possible to clean out the internal water ways if something has got in and gummed up the works?

Thanks again for your comments

 

[aztec]

do you use the boat in shallow water?

a mate had to clean out a block recently which had filled with silt/sand.

<A target="_blank" HREF=http://homepage.ntlworld.com/s.amos/index.html>http://homepage.ntlworld.com/s.amos/index.html</A>

 

[rogerroger]

My thermostat got blocked just due to salt build up - it wouldn't open to let the cooling water through when required.

Sea Start fixed mine and now having seen it done it's quite simple.

Roger Holden
www.first-magnitude.co.uk

 

[philip_stevens]

Following on from Rogers post, I have a BUKH - different engine, yes, but the same thing could happen.

At start-up when the engine is cold, the thermostat is closed. In my engine case, closed to the engine to aid warm up. At the same time, there is a good flow from the exhaust as the cold water is being bypassed by the stat. When the engine is warm, the stat opens to allow "trapped" water in the engine block to flow and mix with the bypassed water and be discharged through the exhaust.

By opening, it thus allows cold water to be able to pass through the engine block to act as a coolant - its purpose.

If after a while you are getting the high-temp alarm come up, I would look at the stat in the first instance, and in fact replace it to eliminate one source of problem. If it is not that, then you could well have a blocked waterway in the block.

regards,
Philip

 

[Thresher]

I have a Volvo MD5 also 1980 and had exactly the same problem earlier this year. I checked the impellor, it was OK. I bought another thermostat, took the old one out, put them both in a pan of water and heated them up. They both opened at the same time so the thermostat was OK. I ran it without the thermostat and it didn't overheat so I put the old thermostat back and the problem never re-occurred! there must have been some muck in there that got flushed out.

There are 3 pipes around the thermostat, one inlet, one exhaust and the top one circulates water through the engine. I found that I could get a picture of what was happening by feeling the temperature of the 3 pipes as the engine warmed up.

 

[Guest]

Thanks to you all. I have checked the impleler (OK) and ordered a new thermostat. I tried to run the engine with the old thermostat out but I couldn't get a seal and water gushed out. I put the old thermostat in a pan, heated it and it opened OK.

I suspect I have some blockage in the water system in the engine. Is there a method of flushing the system? I'm afraid if I just shove a hosepipe in I might do some damage

Thanks

Joe

 

[Thresher]

Joe

I've read in some previous posts about flushing the cooling system with brick cleaner (which I think is hydrchloric acid) to remove any build up of salts in the engine cooling chambers. I've also read about the head of the engine being taken off to remove an obstruction. I think just using a hosepipe wouldn't be vigorous enough.

I take it you have taken the feed pipe off of the thermostat to make sure there is a good flow of water in. Then, if you have a good flow out (ie. the feed and the outlet remain cool but the top recirculating pipe gets boiling hot) I'm afraid you have to try one of the above two options, I can't think of anything else.

Good luck with it, let me know how you get on. I'm not convinced my problem has gone forever.

Brendan.

 

[Paulka]

Hi, Jo,

I didn't intervene yet, not to make you afraid of what's lurking!
I don't know the details about the MD5, but my MD11 (2 cyl. 18 - 20 hp) had the same symptoms after 20 years of good service.
Taking the thermostat away, is of no use, as the total water flow is constant, the thermostat diverting some water TOWARD the engine when it opens, the remainig going strait to the exhaust. Actually, the thermostat looks that the engine doesn't remain too cold, not the other way 'round.
What happened to my engine : the waterways (all of them) inside the block were completely blocked by very hard deposit. To get at it, no other solution than to take the engine to pieces, not forgetting to dismantle the liners! The waterways between the block and the liners, were completly filled with the stuff.
.... And don't dream, there is no other way than hammer and chisel, and a lot of elbow grease to get rid of it.
That's the bad news!

The not so bad one is that Volvo sells - nothing FOC at V***o :-( - a "kit" including liners, pistons, rings etc. thus, no re-boring is necessary. Re-boring the liners may be possible, but you'll need oversized pistons etc. anyway.

Good luck!

Paul

 

[johnt]

descaling engines

sounds like limescale! ...and engines do suffer from scaled up waterways

Im just a little curious as to why you didnt use a descaler instead of a hammer and chisel !

Question; have you ever seen your missus take a hammer and chisel to the kettle?

 

[johnt]

you wont do any damage if you make sure the water comes out again before it gets to the exhaust ..you just wont do much good either ..it needs a descaler to flush it

 

[vyv_cox]

John is correct - kettle descaler is excellent stuff for removing the scale in engines. As someone said earlier up, hydrochloric acid will remove it but there is a risk that it will attack some components of the cooling system as well. Thermostat is one that springs to mind. Better to use kettle de-scaler, a mixture of citric and lactic acids that will not harm any metals. Cheap too, because no-one has recognised that it can be used on boats! Rig up a reservoir to allow you to circulate a solution through the engine and let it sit according to the instructions, from memory about an hour. It doesn't need to be very hot, so don't circulate it for long.

 

[Paulka]

Yes!

We tryied chlohydric acid (HCl) in various concentrations, at no avail!
Some of the stones were put into acid, just to see what would happen, and stayed there for one week without dissolving.
One important point in my opinion, if you want to use acid, is to take the thermostat out, because the "main" circuit for the cooling water bypasses the engine, and directs the water directly to the exhaust. Only when the thermostat opens (or is missing), is the water allowed, but not forced, through the engine. The consequence of this is that, the more slime, the less water, acid, .... whatever will go through the cooling "channels".
The above applies to the Volvo MD2 - MD11. I don't know the details about other engines.
Of course, we (the engineer, and myself) tryied all possible means before using the brute force!
I'm convinced, it was the only way to get rid of the thick (till 1,5 - 2 cm.) and b****y hard stuff.

BTW, except for the first two weeks, when we went through the Canal du Midi, the boat always was in sea water.