Engine overheating.

[Graham_Wright]

Jabsco ok and wet exhaust as expected.
Calorifier hose are cold.
Possibly engine water pump?

 

[tillergirl]

I'd suspect the thermostat first.

 

[scottie]

that is utilising your crystal ball and may even be the case !

 

[VicS]

Jabsco ok and wet exhaust as expected.
Calorifier hose are cold.
Possibly engine water pump?

Possibly the pump Obviously no coolant circulation if the calorifier hoses are cold but that could be air locked.
I'd expect there to be circulation to the calorifier even if the thermostat had failed
But you don't even say what engine so all crystal ball stuff.

 

[Graham_Wright]

Possibly the pump Obviously no coolant circulation if the calorifier hoses are cold but that could be air locked.
I'd expect there to be circulation to the calorifier even if the thermostat had failed
But you don't even say what engine so all crystal ball stuff.

The ubiquitous BMC 1.5 diesel.
It has given me continuing trouble. Time to change for the spare I think.
This was supposed to be a fair weather trip to convince the wife that the prop doesn't always fail to rotate with the shaft, the prop shaft doesn't always fail to rotate with the gearbox output and the engine doesn't always catch fire.
I don't think I have succeeded.

 

[Boater Sam]

Air lock. BMC 1.5D has a cast iron pump, practically always work until they wear out and then they leak but still pump.

Vent the cooling system high points and the calorifier coil connections.

 

[Graham_Wright]

Air lock. BMC 1.5D has a cast iron pump, practically always work until they wear out and then they leak but still pump.

Vent the cooling system high points and the calorifier coil connections.

The highest high point is the heat exchanger which is where the boiling water escapes.
I share your opinion of the water pump and cannot understand how it could suddenly fail.
I just hope it isn't a head gasket or the like.
We are out in the Bristol Channel with no wind and a losk to negotiate. We will taker tide back uip channel and drudge if necessary. It worked for the olds!

 

[Aja]

Jabsco ok and wet exhaust as expected.
Calorifier hose are cold.
Possibly engine water pump?

What do you mean by 'wet exhaust as expected'? Are you getting the expected amount of water or the back end?

Is it a little overheat where you can manage any rise in temp by keeping at tick over or is it a case of screaming alarms?

Have you checked impeller is not impaired - don't know the engine - but is it actually rotating. Is the face plate on the pump flush and not sucking air?

 

[Graham_Wright]

What do you mean by 'wet exhaust as expected'? Are you getting the expected amount of water or the back end?

Is it a little overheat where you can manage any rise in temp by keeping at tick over or is it a case of screaming alarms?

Have you checked impeller is not impaired - don't know the engine - but is it actually rotating. Is the face plate on the pump flush and not sucking air?

Usual amount of water from the transom rules out the sea water side I think.
We need to return to Cardiff Bay (with no wind at the moment) and I can run the engine for a few minutes to pass the lock.
Once on the pontoon, I can investigate.

 

[jlavery]

What temperature is the water coming out of the exhaust?

Cold indicates no heat being exchanged.

Hotter than normal indicates raw water restriction, partial blockage.

 

[Graham_Wright]

Back on the mooring. A fair wind fortunately.
Chief suspect in my mind is the thermostat due to the calorifier hoses being cold.
I'll report back.

 

[Rappey]

Does the engine lose cooling water ? May have got low and created an air lock.
Don't dispair, parts are very cheap. They are great engines. Mine been running faultless for 40 yrs and before that it spent 16 years being thrashed in a van.

 

[Boater Sam]

Back on the mooring. A fair wind fortunately.
Chief suspect in my mind is the thermostat due to the calorifier hoses being cold.
I'll report back.

Very unlikely the stat. If it had failed closed as you "suspect" the calorifier circuit would still be hot as the take off is on the back of the cylinder head and is a bypass around the stat.

 

[Graham_Wright]

Correct - the thermostat tested and ok.
The pump revolves very freely but, if I remember correctly, it is only a "water fan" not positive displacement.
The investigation continues. Pump off next if, nothing else, to eliminate it.

 

[B27]

If the seawater side appears to function and the calorifier is not getting hot, then ISTM the calorifier circuit is not circulating.
I would suspect an airlock.

One test is to take the calorifier out of circuit and replace it with a short hose.

The other potential fault is the coolant pump impeller not actually going around (not the seawater rubber impeller, the closed circuit's water pump centrifugal impeller).
Or it's blocked with dead spiders, gasket cement etc.

 

[Graham_Wright]

I've removed the pump and it is ok (as anticipated).
Water flows through the engine freely.
The calorofier circuit is free (but in parallel with the heat exchanger anyway).
What next?
I wonder if the pump could be sucking air from the calorifier connections.
Next investigation.

 

[Boater Sam]

Is the cooling system pressurising unduly due to a head gasket failure as you mention water loss from the header tank, which you will always get if you overfill when cold as it heats.

If you run with the cap off do you get constant bubbles of gas?

The high point for venting may be a pipe loop rather than the tank or the calorifier.

 

[Graham_Wright]

Vic and B27 suggest air problems and I think that may be the clue.
I disconnected the return from the calorifier and blocked the return entry it shares from the heat exchanger.
With a few minutes run, no sign of overheating but, but importantly, no water exiting from the calorifier hose.
If there is an air leak in the calorofier circuit, that could be the cause.
If I blow into the heat exchanger cap, I can force water through but it requires disconnecting the hose and reconnecting lose water again.
I have a separate header tank to take expansion (ex Vauhall Corsa). The takes the overflow from the heat exchanger filler cap but the feed from it is back into the return from the heat exchanger. If the header tank empties, that connection can suck in air.
Strange I've never had this problem over the last four years.
Where do others make their calorifier connections? We have never experienced more than slightly warm water from the taps.
Fingers crossed and thanks for all the help.

 

[Rappey]

Where do others make their calorifier connections?

There is a outlet at the back of the head on the right. The return is joined to the pipe that goes from the block to the heat exchanger.
I think it uses what use to be the out and in for the vehicle heater.

 

[Boater Sam]

The flow for the calorifier is from the tapping on the top rear of the cylinder head and the return is into the water pump inlet on the port side front of the block. It bypasses the thermostat. If that circuit is air locked the rear cylinders may be under cooled leading to boiling. If the header tank is also the exhaust cooler an air lock there will cause flash boiling once the exhaust gets hot.