Coolant tank very very thirsty - BMC 1.5

[Horsehorn]

Hi,

 

The coolant tank on our BMC 1.5 is gobbling water like there is no tomorrow. We've had some problem with this for a while but have not gotten to fixing yet, so we've been topping up the water every time we use the engine. Having watched the engine in action what seems to be happening is that water is coming out through a small valve just under the coolant tank lid (like an overflow). Somebody suggested there might be an air bubble, but I'm not sure how to tackle it (novices...).

 

I've also heard it mentioned that there's an amazing website somewhere which is a guide to BMC engines? Suggestions?

 

Help much much appreciated, thank you.

 

Lucy

[cereal tiller]

the coolant in the engine does expand as it warms up from cold,

the water level should be 25mm or so beneath the filler cap,dont fill it right to the top,it will overflow till it has finished expanding.

[JonL]

Not a BMC expert , but if it was a petrol engine I would say its a blown head gasket.

A complete expert will be along very shortly

[alan_fincher]

the coolant in the engine does expand as it warms up from cold,

the water level should be 25mm or so beneath the filler cap,dont fill it right to the top,it will overflow till it has finished expanding.

Not just the coolant in the engine, the coolant in the whole system, to include the skin tank, and (if you have one) the calorifier coils.

 

By far the biggest amount of water is generally in the skin tank, though, particularly if not of a sensible design, (if "too thick" it worsens the problem).

 

Leaving the water an inch low in the header tank, when cold, may not be enough on some BMCs, and some are better with just enough water in the header tank that it will still circulate, but leaving a maximum expansion gap.

 

How much air space are you leaving at the top when cold ?

 

If it has started doing it though, but never used to, with the same amount of fill, unfortunately it could be a head gasket failure, as someone has mentioned.

[Guest]

Hi,

 

The coolant tank on our BMC 1.5 is gobbling water like there is no tomorrow. We've had some problem with this for a while but have not gotten to fixing yet, so we've been topping up the water every time we use the engine. Having watched the engine in action what seems to be happening is that water is coming out through a small valve just under the coolant tank lid (like an overflow). Somebody suggested there might be an air bubble, but I'm not sure how to tackle it (novices...).

 

I've also heard it mentioned that there's an amazing website somewhere which is a guide to BMC engines? Suggestions?

 

Help much much appreciated, thank you.

 

Lucy

I have never owned a BMC, but my Vetus did similar from new and the problem was indeed air locking. It required a modification, but this probably wouldn't apply to your engine. A few digital photos of setup might help others who are more knowledgeable pinpoint the problem.

[David Schweizer]

Not just the coolant in the engine, the coolant in the whole system, to include the skin tank, and (if you have one) the calorifier coils.

 

By far the biggest amount of water is generally in the skin tank, though, particularly if not of a sensible design, (if "too thick" it worsens the problem).

 

Leaving the water an inch low in the header tank, when cold, may not be enough on some BMCs, and some are better with just enough water in the header tank that it will still circulate, but leaving a maximum expansion gap.

 

How much air space are you leaving at the top when cold ?

 

If it has started doing it though, but never used to, with the same amount of fill, unfortunately it could be a head gasket failure, as someone has mentioned.

 

The coolant should not be filled to more than about an inch below the bottom of the filler neck or it will just pee out of the pressure relief cap overflow pipe when the water heats up and expands. Of course the other possiblity is that spring in the pressure cap has lost it's tension, and need replacing, the replacement cap should only be 4lbs.

 

If some water still comes out, one solution is to attatch a small length of plastic tube to the overflow pipe under the cap and collect any surplus water in a separate container, if you ensure that the plastic tubing reaches the bottom of the container, most of it will be sucked back into the header tank as the engine cools.

 

When the engine is cold, pour any excess in the overflow container back into header tank and check the coolant level. If it is similar to the previous day, you are putting too much water into the header tank, so next time throw the excess water away and check the following day. You will eventually find the correct level.

 

If the level is still much lower after all that, you have leak somewhere.

Edited September 11, 2011 by David Schweizer

[Mike Jordan]

As the other reply's say its normal to have a space at the top of the tank for expansion. You are right about the little pipe below the cap being an overflow, in some installations this is fitted with a rubber tube which connects to a (normally plastic) header tank which catches the spillage. When the engine cools down, the resulting vacuum will drawn back the spillage into the engine through a little one way valve that you should be able to spot at the bottom of the cap.

The advantage of this system is that you won't be constantly needing to add antifreeze and water in the winter.

An experienced scrap yard raider should be able to find a suitable header tank for very little cost.

Best of luck

Mike

[David Schweizer]

As the other reply's say its normal to have a space at the top of the tank for expansion. You are right about the little pipe below the cap being an overflow, in some installations this is fitted with a rubber tube which connects to a (normally plastic) header tank which catches the spillage. When the engine cools down, the resulting vacuum will drawn back the spillage into the engine through a little one way valve that you should be able to spot at the bottom of the cap.

The advantage of this system is that you won't be constantly needing to add antifreeze and water in the winter.

An experienced scrap yard raider should be able to find a suitable header tank for very little cost.

Best of luck

Mike

I made mine from a Boots screw top liquid soap bottle and a short length of copper pipe. It can be held in an old baked bean tin, fixed it to the bulkhead.

[Mike Jordan]

Calcutt Boats may be the information site you mention, they have a number of downloads available.

 

http://www.calcuttboats.com/engines.html

 

Mike

[Horsehorn]

Thank you everyone. Basic question - Is the header tank and coolant tank the same thing? There's isn't a skin tank.

 

We have been filling it right up, so understandable that the water has been expanding and leaking out of the overflow. I will try David's suggestion however although I am very much at the beginnings of learning I'm pretty sure not this amount of water should be escaping.

 

We bought the boat several months ago (our first) and experienced this problem about a month after purchase, so I can't comment too much on the engine's history. We're pretty sure there isn't a leak as this has been checked by a friend and a boat mechanic (we called him out from the marina where we bought it when there were problems and he said there's no leak - but suggested there might be an air block).

 

How can I tell if there is an air pocket, or far worse, the head gasket has blown? What would the signs be?

 

If the gasket is blown, as I understand it that part isn't so expensive but the problem will be more damage caused by oil/water making it's way to the wrong parts of the engine? If it is the head gasket, is it very urgent to get it fixed to limit damage caused by this?

 

Greatly appreciating your help!!!

[alan_fincher]

There's isn't a skin tank.

So does this engine rely on raw water cooling then ?

 

i.e. Does it pump in canal water and expel it over the side ?

 

If so that is a different set up to what just about everybody who has responded assumed you have, I think!

[Horsehorn]

http://nacnud.info/elysianboats/pdf/bmc.pdf

 

"Do not believe the rumours that you can overheat a 1.5 BMC, seize it solid then let it cool down and restart the engine with no long term damage. This abuse puts a ‘twist’ in the crankshaft, one day when youleast expect it, you will hear a CLONK and a CRUNCH and then complete silence. The crankshaft snaps near the centre main bearing. Overheating causes twisted cranks, reduces bearing life and warps cylinderheads causing head gasket failures."

 

In previous posts I forgot to mention that we had engine cut out, and this above text sounds familiar. If this were the case, would this mean the crankshaft and cylinder heads would have to be looked at in addition to the head gasket?

 

[Mike Jordan]

If the engine has a wet exhaust or or water flows from an outlet when the engine is running, this is normally an indirect raw water cooled installation.These have in inlet filter of some kind, if its blocked the engine will overheat rapidly. If no water escapes when running, there must be a cooling system involving a tank or external pipe/pipes. A photo would help someone to easily identify the cooling method.If you have a failed head gasket you would normally expect to find oil in the cooling water or more frequently water in the sump oil, after running the engine have a look at the dip stick.

Mike.

[Horsehorn]

It's not raw water cooled. When I say skin tank, I understood this to be a plastic expansion thing that catches overflow and directs it back into the system. This may not be a skin tank and so apologies for confusion! It is water cooled, but not direct from the canal.

 

I think it might be the gasket as the water looks pretty sludgy

 

Will take some pics and send them over tomorrow.

 

Thank you again

[alan_fincher]

No,

 

A "skin tank" is the large steel tank on the boat, (usually, but not always on the side of the swim), which actually does the cooling, by exchanging heat with the canal water on the outside.

 

It will have two hose connections to the engine, (should be top to top, and bottom to bottom).

 

If you have one of those, all previous comments apply.

 

It is the volume of water that these tend to hold that most contributes to water being pushed out of an over-full header tank as the engine heats, and the water expands.

 

Some pictures of your set-up might help people spot anything out of the ordinary....)

[Smelly]

Sludgy water might be a lack of antifreeze in the system and corrosion... When did it last have a coolant change?

 

Two ways to check for HG failure...

 

Check the dipstick. Is the oil milky? People refer to Mayonnaise... If so there's coolant in the oil and HG is prime suspect.

 

Second buy one of these. I didn't get brilliant results with one but there was a definite pH shift in the gases from the header. (However as my HG probs were solely related to the harsh cold I still suspect expansion/contraction probs before HG failure)

[alan_fincher]

Two ways to check for HG failure...

 

Check the dipstick. Is the oil milky? People refer to Mayonnaise... If so there's coolant in the oil and HG is prime suspect.

 

The lack of water in the engine oil doesn't guarantee the head gasket is OK.

 

It depends which bit of the gasket has failed, and what is escaping into what.

 

We had an engine eventually proving to have multiple failures of the head gasket, but there was no trace of oil in the engine cooling water.

[Bob18]

A couple of very simple tests, in addition to looking at the dipstick:

First take the oil filler cap off and have a look down the hole. It should be black and oily, but if it has a white fluffy film on it, or the filler cap has the same then its the head gasket that has retired.

Second with the engine cold take the water filler cap off, start the engine and watch surface of the water in the header tank, it should just gently roll as the thermostat opens, you may see the odd bubble (one small one every few seconds at the most), if you see lots of bubbles then the head gasket has almost certainly retired.

 

While these are "head gasket" tests the same symptoms can be caused by several other (far more expensive) problems, including a cracked cylinder head, a warped cylinder head, a cracked block, a cracked cylinder liner (but I don't think the BMC 1.5 diesel had separate liners).

The most common of this list is the warped head, which may follow excessive overheating.

[Evo]

FFS Horse...you need a competent engine guy to look at this...!! No point in you guessing and panicing about what it might be when it sounds like you wouldn't have a clue what you are being told anyway. Any competent bloke who knows anything about engines should know pretty much instantly what it is. In the meantime dont use it.

Edited September 12, 2011 by Evo

[gronny]

Hi there this is my first post on the site! I have a little knowledge (motorbike engines mainly) but i am a complete newbie with diesels and marine engines generally. I have just bought my first boat which has a 1.8 BMC engine (Skin tank but no expansion vessel) and have some similar issues i am working through. I am not discounting a blown CH gasket, but I have no specific indicators / emulsified oil/water so I am trying to discount everything else first.Mainly i am looking to check the items i am capable of doing myself before resorting to costly professional help. hence I hope my experiences and questions may add a little to this discussion.

 

1) i didn't notice anyone suggesting an inspection of all hoses and clips, i allowed the engine to run a while and then inspected (carefully to avoid belts and other running gear)and found a few minor leaks. Tightening the hose clips sorted them out and reduced (not removed!) overall coolant loss.

 

2) Also inspect overall condition of hoses (cracks,splits, overall ageing?

 

3)i wonder what more experienced others may think about the possibility of a faulty coolant tank cap? Could this be allowing excessive coolant leakage? I found white powdery deposits on the tank cover below the filler cap which suggests to me that i have some issues here in the past? As its a relatively cheap item, i wonder if it may be worth replacing this?

 

4)i am also wondering if the coil in the calorifier may have a leak. I get fairly constant drips from the pressure relief valve on the calorifier and wonder if this additional pressure is coming from a leaking exchanger. Is there a means of checking whether the hot water is contaminated with coolant (hence indicating a leak)?

5)some hoses and connections were difficult to view and I have heard you can buy a dye that shows leaks by depositing a bright pink/yellow "tell tale" at the site of a leak. Does anyone have any view/advice/experience on this?

6) Engine temperature when running? does it stay constant and within acceptable range? If not i suggest expert advice right away.

[Chalky]

The lack of water in the engine oil doesn't guarantee the head gasket is OK.

 

It depends which bit of the gasket has failed, and what is escaping into what.

 

We had an engine eventually proving to have multiple failures of the head gasket, but there was no trace of oil in the engine cooling water.

 

Exactly as Alan says. I've had a few petrol B series engines in standard and modified MGs. The petrol and diesel are similar when they let go. The failures I had never put water in the oil. The B series tended to blow between cylinders 1-2 and 3-4 (causes rough running and poor starting) or across the head into the water jacket. The location of the oil gallery in the corner of the head made a blow into the oil gallery unusual. If you keep loosing water then it's got to be going through one of several places. Usual favourite for a car is the water pump or a blown hose. Other locations are the core plugs ,especially if run for a long period with no antifreeze. The last place is into the combustion chamber. When this happened to me the blown head gasket caused the pressure in the cooling jacket to increase and would blow the water out of the header tank overflow. You can check this using a test kit since you'll have combustion products in the water.

 

Never changed the head gasket on a diesel, but on a petrol engine it's a job well within the scope of a home mechanic. I used to be able to change one on an MGB in about 4 hours (which meant I could get to work next day!) Main thing is the engine is cast iron which means the head is heavy...

Edited October 8, 2012 by Chalky

[STIG]

Sorry to be the bearer of bad news Lucy, but my vetus was doing similar earlier in the year, turned out to be 3 cracked cylinder head bolts, no idea how this happenned but costly job.

 

BOAT : Bring Out Another Thousand

 

Remember don`t loose the faith but try to get a `competant` mechanic to take a look

 

Where abouts are you

Edited October 10, 2012 by STIG

[bizzard]

If the cylinder head gasket is at fault i strongly recommend having the cylinder head when removed, crack and warp tested, especially if the engine has been known to seriously overheat and or run short of coolant.

[5thHorseman]

Had a similar problem of water loss, replaced the spring loaded filler cap. Problem solved. Suggest you try this first as it is cheap, quick and easy to do

 

5th

[alan_fincher]

Had a similar problem of water loss, replaced the spring loaded filler cap. Problem solved. Suggest you try this first as it is cheap, quick and easy to do

 

5th

Yes,

 

That is good advice.

 

It may not be that, but it's cheap enough to be worth ruling it out.

 

Generally the pressure cap on a BMC will be no more than about 7 psi - they come in lots of pressure settings, so make sure you don't replace with one that is set too high.