diesel engine heat alarm at low revs

[charles_reed]

The cooling water path in these engines is something of a mystery that has had some discussion on the forum. This pic shows the layout.

Unlike other engines there is no diverter valve to push water through the thermostat after cooling the engine, in preference to passing straight through the tube to the manifold where it does no useful cooling. It seems that cooling depends upon a small restriction at the end of the brass tube but this cannot be excessive or the back-pressure before the thermostat opens would destroy the impeller.

Known problems are that the perforations in the brass tube become blocked by salts. It sounds as if that is what is happening in your engine. At tickover more of the water is passing the restriction at the end of the tube rather than going through the perforations, so the engine is less well cooled. Once the pump output increases the flow through the perforations increases and all is well.

I would not worry a lot at present but if the situation deteriorates it is fairly easy to solve by filling the coolant circuit with a chemical that removes the salts, such as Rydlyme http://www.rydlymemarine.co.uk/

The probability is that the little gods of diesel engines have descended on Dylan's motor and some form of diversionary sacrifice is necessary. Certainly purchasing a Volvo diesel is an open invitation for them to visit.
However, if Dylan can suspend his world-view for a few minutes and try:-

1. Vyv's very practical suggestion (rather than Radlyme I'd use a sulphamic acid descaler http://mistralni.co.uk/products/sulphamic-acid), before trying anything else. Run it through a hot engine, don't pollute the environment so collect from the exhaust and recirculate.
2. If that doesn't work have the waterpump out, machined internally and rebuilt with new seals, bearings etc.

Fiddling about with other things may help to single out the cause but won't solve the problem. It's not super-urgent but is probably better done sooner than later or ignoring it will add the risk of something seriously expensive.
Whatever you do don't use a "qualified marine engineer" - IMHO no such thing exists and it's about time Dylan learnt self-sufficiency, stiff upper lip, understatement and other Brit virtues.

 

[JohnGC]

I had the same symptoms with my MD2020. Not quite as severe but very low flow from the exhaust at idle and overheating at idle after motoring hard.

I traced the problem to a leak in the strainer which was allowing air in (no water leak). In my case one of the hose fitting spigots had collapsed.

It was relatively easy to diagnose using a dinghy pump.
Remove the impeller and refit the pump plate.
Remove the hose from the heat exchanger and connect it to the dinghy pump. Keep the end above the water line if you're afloat.
Pump and listen.
With the raw water inlet open you will hear bubbles under the hull and you may clear mud from the intake.
With the inlet closed, listen for air leaks in the pipework and fittings. You could smear washing up liquid over the joints and look for bubbles but I didn't find that necessary.

This procedure takes about 10 minutes and costs nothing. Personally I'd start with this and move on to the blockage and pump possibilities if you don't find a leak.

 

[James_Calvert]

....

she overheats if on tickover for about five minutes

maybe three minutes on tickover in gear ...

Just a thought, is the engine actually overheating, or has the sensor become oversensitive? That can happen on Bukhs, I don't know about your Volvo. (Hopefully someone will shoot me down if this is rubbish...)

I like your pic of Harmony alongside the pontoon, she looks very smart and purposeful.

James

 

[BruceDanforth]

What is the point of doing the job to fit an impeller and fitting an old one when a new one is about £15?

 

[concentrik]

Four possible causes I can think of:

1. The cooling system itself is fine but not enough external (from the sea!) cooling water is available

2. Enough cooling water is available but it is not being forced (pumped) into the cooling system

3. There is enough external water available and it is being forced into the system but the flow path is constricted resulting in low flow

4. The engine is producing too much heat for the cooling system to dissipate even if that system were in perfect order.

You say that there is no obstruction to the inlet so (1) is probably OK

It seems unlikely that (4) is the reason - there is plenty of overcapacity for cooling so the engine would need to be producing far more heat than normal. I'm assuming you don't have it wrapped in a duvet.

So that leaves (2) and (3).

If you disconnect the output from the pump and run the engine for a short while you should see a unmanageable quantity of water emerging. You should get very wet if unprepared. Putting your thumb on the open end will be difficult. You have shown that the intake, pump and strainer are good.

If you reconnect the pump output and disconnect at the next available point you can check water flow through each section of the cooling system. I don't know the engine so there may not be so many points to do this. But the principle is the same - establish good pump pressure then find where the pinch point is. The fact that it does cool sufficiently at higher revs when not under load (more heat) does suggest flow constriction to me. You need to find out where. My personal favorite is the oil cooler, lots of tiny tubes bunged up with twenty years of old impellor bits, nuts, studs, old crisp packets etc

 

[dcr]

Don't forget to remove and inspect the exhaust elbow. We had similar problems with our 2003 - fitted new imeller then complete new pump. Plenty of water "in" but not enough flow out so overheated. Inspection of the elbow showed it was badly choked with carbon deposits which after removing and cleaning the engine performed OK.
Good luck
dcr

 

[dylanwinter]

Before you go spalshing out on spares and getting involed in engineering work measuring clearences and cam runout etc. Check that the strainer lid isn't leaking air in. Start with the simple stuff first is my motto..........

The prize goes to BarryH and JohnGC

unairtight water strainer

There was a pot of vaseline in the tool box

when I opened up the strainer there was no rubber seal in the top - as I had on the slug

she is now pumping prodigous quantities of water through the exhaust at tick-over

been running for ten minutes and no alarm

thanks guys

Bog problem is as yet unsolved

D

 

[JohnGC]

Bog problem is as yet unsolved

D

If the vaseline doesn't work, try sennapods

 

[Colvic Watson]

If you disconnect the output from the pump and run the engine for a short while you should see a unmanageable quantity of water emerging. You should get very wet if unprepared. Putting your thumb on the open end will be difficult. You have shown that the intake, pump and strainer are good.

If you reconnect the pump output and disconnect at the next available point you can check water flow through each section of the cooling system. I don't know the engine so there may not be so many points to do this. But the principle is the same - establish good pump pressure then find where the pinch point is. The fact that it does cool sufficiently at higher revs when not under load (more heat) does suggest flow constriction to me. You need to find out where. My personal favorite is the oil cooler, lots of tiny tubes bunged up with twenty years of old impellor bits, nuts, studs, old crisp packets etc

Thanks, that's a really helpful description.

 

[Billba]

So back to the OP ref slow starting. It has been mentioned more than once but I haven't seen any reply confirming your understanding of the starting from cold procedure. It will result in reducing your start time from 10 secs plus to 2 to 3 secs. I watched the video of the first start and it didn't feature but may have already been done. Simply set the throttle (out of gear) and pull and release the 'stop' lever which will engage a cold start/extra fuel in the right place set up in the fuel system. Saves flogging the battery and every little bit counts.

 

[dylanwinter]

yup

So back to the OP ref slow starting. It has been mentioned more than once but I haven't seen any reply confirming your understanding of the starting from cold procedure. It will result in reducing your start time from 10 secs plus to 2 to 3 secs. I watched the video of the first start and it didn't feature but may have already been done. Simply set the throttle (out of gear) and pull and release the 'stop' lever which will engage a cold start/extra fuel in the right place set up in the fuel system. Saves flogging the battery and every little bit counts.

no manual for the engine

but found a tear out from PBO that told me to do half throttle , lift the stop, then dropit back then fire it up

it started after about eight seconds - I will post the film, think I need full throttle next time

never heard of such a weird procedure

the button on the beast to supply extra fuel made sense

not sure I understand how this works

on the boat - wind starting to pip up again

D

 

[Billba]

See if this works for you...

http://vppneuapps.volvo.com/ww/PIE/...1-25-08-47-27&t=PDF&a=7746291&p=T403&d=Owners Publication&s=2512225&lang=en-GB

 

[dylanwinter]

See if this works for you...

http://vppneuapps.volvo.com/ww/PIE/...1-25-08-47-27&t=PDF&a=7746291&p=T403&d=Owners Publication&s=2512225&lang=en-GB

bless you for that link

downloaded and being carefully scrutinised, read, learned and inwardly digested

http://vppneuapps.volvo.com/ww/PIE/ViewFileFrame.aspx?n=172231&r=2006-01-25-08-47-27&t=PDF&a=7746291&p=T403&d=Owners[/url]%20Publication&s=2512225&lang=en-GB

 

[parbuckle]

Pleased you have solved the problem I had a similar thing on my Perkins Perama I used a good method of temporarily substituting the hoses connecting the raw water both sides with transparent pipe this gives a good indication of flow especially when underway as the best size and layout of the inlet pipe is not easily known.

 

[Bilgediver]

no manual for the engine

but found a tear out from PBO that told me to do half throttle , lift the stop, then dropit back then fire it up

it started after about eight seconds - I will post the film, think I need full throttle next time

never heard of such a weird procedure

the button on the beast to supply extra fuel made sense

not sure I understand how this works

on the boat - wind starting to pip up again

D

This does exactly what you did on the beast......Gives extra start fuel till the governor takes over
however the manual says full throttle ( fuel ) ..... Check the copy front page you just downloaded.

If you have a miss start then REPEAT the cold start procedure before the next attempt.

For some mysterious reason these instructions are not in all world wide manuals!!!

 

[VicS]

bless you for that link

downloaded and being carefully scrutinised, read, learned and inwardly digested

There is also a workshop manual on Bluemoment which might be worth keeping a note of http://bluemoment.com/downloads.html

BTW it struck me that the overheat alarm came on very quickly. Normally it takes much longer to get an engine up to normal temp.
Was it actually an alarm on the exhaust ... that would come on very quickly if there is little or no water flow