BMC airlock? or something more expensive?

[HappyBunny]

I'm a somewhat confused and concerned bunny ....

 

After my recent "mishap" (see another thread) the head came off, valves reground etc etc etc and went back on fine, and decoked too. She ran sweet for a couple of short slow days, with locks and swing bridges, then noticed she seemed hotter than usual and occasional bubble of air coming up into header tank. No hot water from calorifier.

 

Tested thermostat and removed as knackered, still seemed to be running hotter than before (temp sensor knackered too) (I know).

 

Thermostat replaced, system bled ..... hot water by the gallon ....hurrah .... but still the water header tank rising much more than before head work, and still getting the odd bubble of air coming up especially when cruising at normal speed (1500 rpm) for a long distance .... she is not boiling though ..... and today, no hot water again after 4 hours......

 

The head gasket was checked and seems ok .... and the water was forced through the calorifier system with a hose pipe

 

Any speculation welcome .... is it possible there is still some air in the system, and if so, how do I get rid of it?

.... or am I looking at other more scary / expensive causes?

cheers in anticipation

[Troyboy]

I suspect you still have some air in the system . I had the same problem with my calorifier many years ago and if I remember correctly I loosened off the pipe that connected from the engine to the calorifier at the calorifier end and let a small amount of water out before tightening the hose joint [ a hose clip in my case ] . I then done the same on the pipe that takes the water back into the engine . The experts will hopefully be along in a moment but that worked for me . My engine is also BMC 1.5 .

[Tony Brooks]

I have always loosened the calorifier return pipe at the engine end and twisted it to make sure I could pull it off.

 

Got assistant to stand by to top up header tank

 

Set engine to maybe 1000 to 1200 RPM

 

Pull said connection off and quickly place thumb over the engine side of the disconnected joint.

 

Allow coolant to spurt from pipe and after 30 seconds or so if no air has come out refit pipe & tighten.

 

If by chance the pipework is collecting air from elsewhere in the calorifier circuit see if you can fit a central heating bleed Td into the highest point.

[HappyBunny]

currently scouring the deserted towpath for a likely looking lovely assistant to press gang into action .... physically impossible to do alone with my set up..... thanks both of you

[bizzard]

If you can't manage to bleed the calorifyer ect, doing the following should-might do the job. There is probably air trapped in the cooling skin tank also. Run engine up until normal running temp is reached, remove coolant cap at header tank, heat exchanger or wherever, have some topping up coolant on hand. Rev the engine up and watch for air bubbles coming up and popping in the header tank, keep reducing to idle and blipping up the throttle lever alternately frequently watching for escaping air at the header tank filler, topping up with coolant if needed. If the coolant level heaves up and down by a large amount of its own accord this mean there's still a lot of trapped air present, keep revving and idling the engine until the big heaving up and down and bubbles stop entirely and the level stays more or less steady. Top up to your normal level and replace the cap.

[HappyBunny]

"Heaving" is the word .... I am going to get up to the water tap at Calveley (assuming my cunning plan to single hand Beeston Iron lock works, or I meet some helpful boaters/walkers) and have a good furtle, armed with all this advice.

 

I am also wondering how, if, and where, air might be getting in to the calorifier system? ..... I have always needed to top up my header tank, not much, each week but lately every few days .... maybe a leak somewhere .... or just the air leaving the system ....

 

The words "cracked" and "head" had been bandied about a liitle too much for comfort when discussing my "heaving" problems ..... maybe it wasn't my engine they were referring too .......

[Tony Brooks]

I notice you do not specifically say that you are bleeding the skin tank (assuming its tank cooled). If you are not and if there is no bleed pipe direct from the top of the skin tank (may be a filler pipe) then although it looks as if you have filled the system the tank will be mainly full of air which will begin to move once you start running the engine. So rule number one on tank cooled boat is to find the tank bleed screw/plug/cap and have several goes at bleeding it both while filling and while running and stopped.

 

You should also manipulate any hoses that have loops in the that can trap air so the air moves to the engine where it will exit the filler or to the tank where you can bleed it out.

 

I would also like you to run the engine with the filler cap off until you are sure the thermostat has opened - then a bit longer. This will maximise coolant flow and hopefully shift more air from the pipes.

 

If any small air or gas bubbles move around the system then they tend to collect at a high point and that is often in a calorifier feed or return pipe.

 

Either air or gas will produce these symptoms so once you are sure all the air has been bled out of the system you are left with gas from combustion and unfortunately that points to a head, cylinder, or gasket failure but the rising water in the header tank also speaks of expanding air.

 

Were the head and block faces checked with a straight edge and feelers for truth once they had been cleaned up? It is not unknown for BMC block faces to sink between two cylinders (often 2 & 3). Likewise the heads can also distort, especially when badly overheated and refilled with cold water while still hot.

 

You can get a fluid that you mix with a sample of coolant that reacts to exhaust gas and that will either allay or confirm your worst fears.

[HappyBunny]

Tony ... yes,skin tank bled .... and the head and block were checked and true ..... but I don't think the head was checked for cracks, which might have been advisable while it was off ...

 

Quick update ... I was using the bizzard method until an unsuspecting neighboring boater came to see "if I was having problems" and was then pressganged into action and the Brooks/troyboy method was employed......good job winding a baby isn't this complicated .... she has heaved once and released air, and let out a couple of small bubbles since, but otherwise seems to be running as she used to, with just minor fluctuations in the water level in the header tank ..... so paws crossed that it was just trapped wind ...... but I shall keep a watchful eye on her .... and maybe invest in some of the fluid to check for exhaust gasses

 

Many thanks for clear instructions and help

[bizzard]

Tony ... yes,skin tank bled .... and the head and block were checked and true ..... but I don't think the head was checked for cracks, which might have been advisable while it was off ...

 

Quick update ... I was using the bizzard method until an unsuspecting neighboring boater came to see "if I was having problems" and was then pressganged into action and the Brooks/troyboy method was employed......good job winding a baby isn't this complicated .... she has heaved once and released air, and let out a couple of small bubbles since, but otherwise seems to be running as she used to, with just minor fluctuations in the water level in the header tank ..... so paws crossed that it was just trapped wind ...... but I shall keep a watchful eye on her .... and maybe invest in some of the fluid to check for exhaust gasses

 

Many thanks for clear instructions and help

If you sniff at the header tank filler when hot you should smell exhaust gases if the coolant is contaminate with it.

[RLWP]

I'd wait until you have made a few trips out before worrying about the cracked head. Your boat will probably burp a few more times yet, so the level when cold will fluctuate for a while.

 

Also, you'll probably overfill the header tank a few times and she'll spit out the excess giving the impression of fluid loss*. Be patient and see what happens

 

Richard

 

*I often do

[HappyBunny]

I'd wait until you have made a few trips out before worrying about the cracked head. Your boat will probably burp a few more times yet, so the level when cold will fluctuate for a while.

 

Also, you'll probably overfill the header tank a few times and she'll spit out the excess giving the impression of fluid loss*. Be patient and see what happens

 

Richard

 

*I often do

 

Yes ... I have noticed this forum is such a great place to get help and soothe worries ...... much Happier Bunny now .... have a weekend of weddings and parties then a few days of relatively lock free boating (after Audlem) to see how she goes