Pampered engine still overheating (BMC 2.2). Advice please!

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mikeakc

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Hi all,
I have a BMC 2.2 with a Bowman heat exchanger which is overheating. These are the works / checks I carried out this winter:
  • Oil change
  • Raw water impeller change
  • Thermostat replaced
  • Coolant changed (red)
  • Heat tube stack in the heat exchanger cleaned with vinegar
  • Raw water lines flushed with rydlime
  • Raw water intake checked (looks clear) and exhaust pumping water nicely

Despite the above, the engine reaches 100 C very quickly (10 mins or so). I have confirmed the accuracy of temp readings with an infared thermometer, so the sender and gauge are not giving false readings. I'm running the engine very gently, just above idle really which gives me 4.5 knots. If I push it any more she will hit 105-110 C in a heartbeat.

Just for comparison, a couple of weeks ago I sailed to Scilly on a mate's boat and we motored back due to lack of wind. His BMC 1.8 sat at 75 C for 13 hours without a hiccup. Having seen that I'd love to sort mine out. So, on to the golden question. What do you think it could be and how can I sort it?!

Thanks for any advice in advance,
Mike
 
Looks like your checks give the all clear to the raw water side of the system. So that means I think, the engine coolant circulation side is at fault. Did you test as well as replace the thermostat? Is the engine coolant pump testable/replaceable as Ian suggests? Can these engines get airlocks or blockages? Likely greater wisdom will be along soon.
 
Is it worth taking out the stat and running without to see results. Our is a bmc 1.5 and water pump is on the front face of the block and not easy to get at(bulkhead wise)
 
iantomlinson said:
Is it worth taking out the stat and running without to see results. Our is a bmc 1.5 and water pump is on the front face of the block and not easy to get at(bulkhead wise)
Click to expand...
Hi @iantomlinson, It had no stat in it at all until this season (only established this when I went to replace it). Thanks for the suggestion though.
Mike
 
dovekie said:
Looks like your checks give the all clear to the raw water side of the system. So that means I think, the engine coolant circulation side is at fault. Did you test as well as replace the thermostat? Is the engine coolant pump testable/replaceable as Ian suggests? Can these engines get airlocks or blockages? Likely greater wisdom will be along soon.
Click to expand...
A bit of research suggests the pumps are hard to source these days. Hopefully airlocks, do you have any suggestions as to how / where I can release or bleed these airlocks? Thanks again, all advice much appreciated.
 
mikeakc said:
A bit of research suggests the pumps are hard to source these days. Hopefully airlocks, do you have any suggestions as to how / where I can release or bleed these airlocks? Thanks again, all advice much appreciated.
Click to expand...
You are correct, the internal water pump is difficult to source and very expensive if you can and was part of the impetus for us to replace our BMC.

As the internal and the raw water pump are run off the same pulley (one will not run without the other), my suspicion as to your overheating problem would be the thermostat, as others have suggested. Remove it and test it on the stove top in a pot of water to check that it opens, which it should do at about 80 degr. centigrade.
 
mikeakc said:
Hi all,
I have a BMC 2.2 with a Bowman heat exchanger which is overheating. These are the works / checks I carried out this winter:
  • Oil change
  • Raw water impeller change
  • Thermostat replaced
  • Coolant changed (red)
  • Heat tube stack in the heat exchanger cleaned with vinegar
  • Raw water lines flushed with rydlime
  • Raw water intake checked (looks clear) and exhaust pumping water nicely

Despite the above, the engine reaches 100 C very quickly (10 mins or so). I have confirmed the accuracy of temp readings with an infared thermometer, so the sender and gauge are not giving false readings. I'm running the engine very gently, just above idle really which gives me 4.5 knots. If I push it any more she will hit 105-110 C in a heartbeat.

Just for comparison, a couple of weeks ago I sailed to Scilly on a mate's boat and we motored back due to lack of wind. His BMC 1.8 sat at 75 C for 13 hours without a hiccup. Having seen that I'd love to sort mine out. So, on to the golden question. What do you think it could be and how can I sort it?!

Thanks for any advice in advance,
Mike
Click to expand...
The engine water pump is a very simple device & seldom gives trouble - the mechanical seal may give in but that is a leak & not what you have.Test without thermostat as others have said.
Jim
 
Another thought! Stat out. Fanbelt off. Open each end of engine coolant. Hosepipe in one end. Just to make sure there's flow through engine system. See if pump spins.
 
Is the propeller the correct pitch? Check that you can reach the correct maximum revs. I've had issues with my Beta engine overheating when I push it and decreasing the pitch of the propeller by an inch solved it. If you've tried everything else it could be worth a shot.
 
mikeakc said:
Thanks for any advice in advance,
Mike
Click to expand...

I agree that the thermostat double checked to see it opens when placed in hot water in a pan also check the opening temperature using wifes cooking thermometer. As others have said make sure you still have an impeller on the engine coolant pump. However one thing not mentioned so far is wether your thermostat is the correct one. Some engines can suffer airlocks in the thermostat housing. This can prefent the hot water reaching the thermostat so it fails to open. If this is possible in your engine then check if your thermostat element has a small hole (<2mm) drilled through it to let this air dissipate and fill this space with water.
Is there a chance the thermostat is the wrong way round?
 
mikeakc said:
A bit of research suggests the pumps are hard to source these days. Hopefully airlocks, do you have any suggestions as to how / where I can release or bleed these airlocks? Thanks again, all advice much appreciated.
Click to expand...
Laminar Flow said:
You are correct, the internal water pump is difficult to source and very expensive if you can and was part of the impetus for us to replace our BMC.

As the internal and the raw water pump are run off the same pulley (one will not run without the other) . . .
Click to expand...

It may not be of help to the OP, but if others are suffering from a failing pump that is no longer available at a manageable price, they can be replaced by a proprietary pulley driven pump (will need to fabricate a bracket to mount it on) or electric pump. E.g. Flexible Impeller Engine Cooling Pumps
 
mikeakc said:
Hi @iantomlinson, It had no stat in it at all until this season (only established this when I went to replace it). Thanks for the suggestion though.
Mike
Click to expand...
Was it overheating last season without thermostat ??.If you PM me your email I can give you some tips if you want to take the pump out.I have just had a BMC 2.5 pump rebuilt,it should be the same pump & the impeller was cast iron & no sign of corrosion.
Jim
 
mikeakc said:
Hi all,
I have a BMC 2.2 with a Bowman heat exchanger which is overheating. These are the works / checks I carried out this winter:
  • Oil change
  • Raw water impeller change
  • Thermostat replaced
  • Coolant changed (red)
  • Heat tube stack in the heat exchanger cleaned with vinegar
  • Raw water lines flushed with rydlime
  • Raw water intake checked (looks clear) and exhaust pumping water nicely

Despite the above, the engine reaches 100 C very quickly (10 mins or so). I have confirmed the accuracy of temp readings with an infared thermometer, so the sender and gauge are not giving false readings. I'm running the engine very gently, just above idle really which gives me 4.5 knots. If I push it any more she will hit 105-110 C in a heartbeat.

Just for comparison, a couple of weeks ago I sailed to Scilly on a mate's boat and we motored back due to lack of wind. His BMC 1.8 sat at 75 C for 13 hours without a hiccup. Having seen that I'd love to sort mine out. So, on to the golden question. What do you think it could be and how can I sort it?!

Thanks for any advice in advance,
Mike
Click to expand...
check for gunge in the header tank.
have you had the tube stack out of the header tank, as therer could be an alu gell blocking the freshwater side. take it out and pressure wash. particularly if antifreeze hasnt been changed, until recently.
blockage, or air lock to heat exchanger.
thermostat is missing its jiggle pin or a small hole . or defective, boil it in a saucepan.
what happens if run without thermostat
fresh water pump impeller has failed.
 
The only things that can really fail on the internal cooling circuit pump are the bearing and the ceramic seal. I have fixed enough of these in various exotic locations to know, but for a BMC, Boulogne sur Mer is already a very exotic location, apparently.
If the belt is still intact and the pulley still turning, the pump is still working. Even if it were leaking from the shaft/drip hole and the bearing was rattling like a piggy bank.

If there is plenty of water coming out of the exhaust, the raw water pump is also working fine. If the engine overheats in idle after a few minutes without load, my money is on a defective thermostat.
 
Working on worst case scenario, you say stat was already out last year?? If that was from previous owner, that is a big hint of a cover up for head gasket going and sell quick. Just throwing all sides of the dice sorry.
 
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