Overcooling BMC 1.5

[theclans]

I have an interesting problem which appears to be seldom discussed on the various forums regarding my keel cooled BMC. It struggles to reach the correct operating temperature (82oC stat) and appears to cool excessively when under load resulting in constantly high oil pressure.

 

I tried replacing the thermostat but this didnt help. My current diagnosis is that somehow the coolant is getting passed the thermostat even when closed, and under load the cooling is increased due to increased water circulation through the brass jabsco assisted keel cooling circuit.

 

Does anyone else have any thoughts on what might be causing this and any possible remedies?

 

I was thinking of testing this tonight by removing the housing and holding the stat down and running the engine. Presumably (!!) no coolant should come gushing out while the engine is still cold?

 

If so, I guess the thermostat is not sealing correctly - are there any washers etc which may help?

 

Many thanks

 

Rob

Edited May 3, 2006 by theclans

[David Schweizer]

I have an interesting problem which appears to be seldom discussed on the various forums regarding my keel cooled BMC. It struggles to reach the correct operating temperature (82oC stat) and appears to cool excessively when under load resulting in constantly high oil pressure.

 

I tried replacing the thermostat but this didnt help. My current diagnosis is that somehow the coolant is getting passed the thermostat even when closed, and under load the cooling is increased due to increased water circulation through the brass jabsco assisted keel cooling circuit.

 

Does anyone else have any thoughts on what might be causing this and any possible remedies?

 

I was thinking of testing this tonight by removing the housing and holding the stat down and running the engine. Presumably (!!) no coolant should come gushing out while the engine is still cold?

 

If so, I guess the thermostat is not sealing correctly - are there any washers etc which may help?

 

Many thanks

 

Rob

 

This problem did come up a while ago, and from recollection it transpired that there are two types of thermostat and two types of thermostat housing fitted to the BMC 1.5 . One type had a by pass wheras the other type did not. I think that John Orentas came up with a solution last time.

[John Orentas]

Hi Rob.

 

First there is realistically no such thing as 'high oil pressure', if the pressure stays consistently high it means your engine is in good condition, are you sure you have the correct thermostat, it will have the temperature stamped on it, if you suspect it opening prematurely stick it in a pan of water and watch it open and close.

 

The thermostat does not close off all the water supply, just that flowing round the cylinder head even when it is closed water will continue to circulate around the block of the engine so in theory though not likely, if you have a very strong flow from the pump and a very light load on the engine I suppose the engine could over-cool.

 

You can't run the engine with the top housing removed, water will pump straight out.

 

Edit. Wasn't me David but it sounds logical. As I always say there were thousands of variations of these engines.

Edited May 3, 2006 by John Orentas

[theclans]

Thanks for your replies - just checked out the other thread regarding bypass-v non bypass stats, most interesting.

Not sure if my issue is related to that thread, since my problem is too much cooling!

Regarding the issue of whether my stat is the correct one and functioning - the new one I've bought is from ASAP and is the standard 82oC one they sell for the BMC 1.5. Didnt look exactly like the old one but close enough. Incidently the old one seemed in working order so I'm not convinced the stat is the problem.

 

I forgot to mention that the manifold and keel cooling hose are getting hot shortly after starting the engine (when gauge still reading 40oC - its minimum reading). I've taken this to mean that water is indeed getting into my cooling circuit too soon ie before the engine is up to temperature.

 

Having never replaced a thermostat before I was a little concerned when I dropped it in - didnt seem to be a particularly tight fit and there was no washers or o-rings involved. Should the housing effectively clamp down on the theromstat to make the seal?

 

Cheers

 

Rob.

[alan_fincher]

This problem did come up a while ago, and from recollection it transpired that there are two types of thermostat and two types of thermostat housing fitted to the BMC 1.5 . One type had a by pass wheras the other type did not. I think that John Orentas came up with a solution last time.

Not exactly David.

 

It was me who raised it, and there are certainly different types of thermostat possible that will fit the BMC B series engine, (but I don't know if there are different consideration between the 1.5 engine, and the 1.8 that I have....)

 

Here's a link to the gallery photo I posted before....

 

Link to image of 2 stats

 

What is on the left is a conventional stat, which is what Calcutt tried to tell me was correct for my engine. Despite them being the BMC experts, I don't think they are right about this, (sorry Calcutt!...)

 

On the right is the one fitted, which has an extra part. This I'm led to believe is what's called a "Bypass stat".

 

I believe the purpose of the extra bit on the bottom is to close off an internal pipeway, (in the 1.8 BMC, at least), which allows cooling water to recirculate directly in the engine, and to bypass the cooling circuit. As I understand it, this allows the pump to just recirculate water in the engine, until the stat opens. Once the stat's operating temperature is reached, as it moves down, and opens the pathway to the cooling circuit, the extra plate closes OFF this internal bypass in the engine, so water has to flow through the cooling circuit.

 

Even assuming the same issue exists for a 1.5, I'd still expect that if the wrong stat were fitted, (i.e. a non-bypass one, in an engine that needs one because it has the bypass circuit), then I'd expect the likely result to be OVER-heating, not under-cooling. (Because at least some of the water that was above the temp required to open the stat was just being recirculated internally, without going to the cooling circuit).

 

What Rob describes is the opposite, namely that water would appear to be going into the cooling circuit even before the stat should be opening, meaning that he never measures a temperature as high as the stat's operating temperature.

 

That sounds like the stat is open, or at least passing water, before that water is at the temperature stamped on the stat. (and he appears to have eliminated just a failed stat, by trying another...).

 

I can't immediately see how this could occur from using a bypass stat where you shouldn't, nor not using one when you should not.

 

I've just found this link, again, that may explain the possibilities better than my inadequate ramblings....

 

Link to web page about bypass thermostats.

 

But some questions.....

 

1) Does your thermostat look like the one on the left, or the one on the right ?

 

2) Were original and replacement in the same style ?

 

3) Have you tested both, just by hanging them in water in a saucepan, and heating it, to see that they open and close as expected ?

 

4) Whilst your engine heats up from cold, if you feel the hose coming away from your thermostat housing, towards your cooling circuit, is that getting significantly hot, even when the temperature guage indicates you are yet nowhere near the stat's operating temperature ?

 

5) Does the themostat housing actually contain a bypass hole at the bottom, that a bypass stat would close off ?

 

It if does, it would look something like the hole in the middle here....

 

Another gallery link

 

This is an obscure area, but I'm convinced that correct stat type is vital to correct operation of these engines, (despite some people thinking I was on a hobby-horse before). I found it an area where it's incredibly hard to separate fact from fiction, unfortunately, but the information in the web-link I have enclosed seemed scientifically sound to me, and is the only reliable stuff I've really seen written down about this.

 

Alan

Edited May 3, 2006 by alan_fincher

[alan_fincher]

Thanks for your replies - just checked out the other thread regarding bypass-v non bypass stats, most interesting.

Not sure if my issue is related to that thread, since my problem is too much cooling!

Regarding the issue of whether my stat is the correct one and functioning - the new one I've bought is from ASAP and is the standard 82oC one they sell for the BMC 1.5. Didnt look exactly like the old one but close enough. Incidently the old one seemed in working order so I'm not convinced the stat is the problem.

 

I forgot to mention that the manifold and keel cooling hose are getting hot shortly after starting the engine (when gauge still reading 40oC - its minimum reading). I've taken this to mean that water is indeed getting into my cooling circuit too soon ie before the engine is up to temperature.

 

Having never replaced a thermostat before I was a little concerned when I dropped it in - didnt seem to be a particularly tight fit and there was no washers or o-rings involved. Should the housing effectively clamp down on the theromstat to make the seal?

 

Cheers

 

Rob.

Sorry Rob, just cross posted with you.

 

You have already answered many of the questions I asked.

 

I agree with your diagnosis, if the hose is getting hot straight away. It's behaving as if no stat were fitted, or the one that is is stuck open, (but as you have tried two, it wouldn't seem to be that simple).

 

They do simply drop into the housing, not a particularly tight fit, and no washers or o-rings, just the gasket between the housing and its cover, (which should be trapping it down, stopping most vertical movement).

 

Some water must get forced around the sides, I guess, but this would be minimal, I'd have thought, not enough that you'd feel it as a warming pipe.

 

I'm really out of ideas, I'm afraid.

 

Except.....

 

And I'm not taking the p*ss, (honestly), but it is in there the right way up is it, (same way as in my pictures!).

 

Well, I'm trying to eliminate everything !?!

 

Alan

[theclans]

....just the gasket between the housing and its cover, (which should be trapping it down, stopping most vertical movement).

 

Hi alan, sorry I'm cross posting now! This gasket you speak of - could you provide more details. Does the gasket 'trap down' the stat or is the stat in direct contact with the housing (I mean cover thing..?)

 

Cheers

 

Rob

Edited May 3, 2006 by theclans

[alan_fincher]

Hi alan, sorry I'm cross posting now! This gasket you speak of - could you provide more details. Does the gasket 'trap down' the stat or is the stat in direct contact with the housing (I mean cover thing..?)

 

Cheers

 

Rob

From memory, the gasket has at least as big a hole in it as the diameter of the stat.

 

So I think the gasket is purely a seal, and plays no part on holding the stat in place.

 

I think the stat is trapped between the lower housing, (where it sits in a suitable indent), and the cover, (which I seem to recall is totally flat).

 

But I've only pulled one apart once - someone else may know better....

 

Alan

[bottle]

Thermostats, over-cooling, pipes getting hot.

 

Perhaps it is the temperature guage.

[alan_fincher]

Thermostats, over-cooling, pipes getting hot.

 

Perhaps it is the temperature guage.

 

But what about....

 

I forgot to mention that the manifold and keel cooling hose are getting hot shortly after starting the engine ......

 

Whatever the temperature guage says, I'd expect the engine to spend some time coming up to the operating temperature of the stat, before it opens and hoses in the skin tank circuit start to heat significantly.

 

If the hoses are getting hot almost as soon as the engine is started, it doesn't sound right to me, (and certainly not how mine works). That sounds like the stat failing to do what it should do, for whatever reason.....

 

I think it's more than an instrumentation malfunction....

 

Alan

[bottle]

shortly after starting the engine

 

How long (time) is shortly, going back to the original post, has this always been a 'problem' or has it just started.

[theclans]

How long (time) is shortly, going back to the original post, has this always been a 'problem' or has it just started.

 

Seems to have been a problem since I got the boat last year. I'm only just getting round to doing something about it, because of an endless list of other engine/boat issues that took priority.

 

Anyway, thanks for all the replies - feeling a bit bad as I couldnt get in to the engine last night so cant report back on findings.

 

From the responses I am thinking that it can only be due to coolant getting past the stat somehow, probably because its not sealing correctly (definatley not upside down!!) but possibly because of some faulty bypass system.

 

I'll try and get in tonight and have a look...

 

Cheers

 

Rob

[alan_fincher]

Seems to have been a problem since I got the boat last year. I'm only just getting round to doing something about it, because of an endless list of other engine/boat issues that took priority.

 

Anyway, thanks for all the replies - feeling a bit bad as I couldnt get in to the engine last night so cant report back on findings.

 

From the responses I am thinking that it can only be due to coolant getting past the stat somehow, probably because its not sealing correctly (definatley not upside down!!) but possibly because of some faulty bypass system.

 

I'll try and get in tonight and have a look...

 

Cheers

 

Rob

No problems.....

 

That's how it goes....

 

If you do have the stat out at any stage, and have access to a digital camera, can you take a photo both of it, and what's down the hole, inside the housing, and post in the gallery.

 

Perhaps also some snaps of your general arrangement of pipes / pump / skin tank, as I think you mentioned having a Jabsco in there, (whlist mine relies solely on the original engines water pump to circulate water through the skin tank circuit).

 

Pictures often give people more to go on than words, I think.....

 

Alan

[theclans]

Ok, this is a very difficult post to write.

 

...when I said "definately not upside down", what I meant was that I put it in the same way up as the one I took out. Given that the engine had supposedly just been "reconditioned", I assumed this would be correct and thought no more about it.

 

Knowing more now, imagine my surprise when I pulled the housing off and saw the spring sticking out of the top!!!

Inserted in correct orientation and now all is well and good.

 

What a fool, and sorry to waste peoples time - but thanks for all the replies.

 

Now just got to sort out the misfiring, diesel in oil, and oil pressure issues but thats another topic altogether.

I'll do some more investigations first this time!!!

 

Cheers

 

Rob

 

PS On the thermostat difference issue, didnt have a camera available but there were subtle differences between the old and new ones. However the old one was definatley not a bypass type with the lower washer. It just had a hole in the "rim" bit with some sort of pin in it (presumably to let a small amount of coolant/air out from engine side? but not back the other way). The new one does not have this - should it?

Edited May 5, 2006 by theclans

[alan_fincher]

...when I said "definately not upside down", what I meant was that I put it in the same way up as the one I took out. Given that the engine had supposedly just been "reconditioned", I assumed this would be correct and thought no more about it.

 

Knowing more now, imagine my surprise when I pulled the housing off and saw the spring sticking out of the top!!!

Inserted in correct orientation and now all is well and good.

 

Cheers

 

Rob

 

No problem at all Rob!...... At least it's a nice cheap one to fix, which can only be a bonus, (though I'd have some worries about the "reconditioner"....)

 

PS On the thermostat difference issue, didnt have a camera available but there were subtle differences between the old and new ones. However the old one was definatley not a bypass type with the lower washer. It just had a hole in the "rim" bit with some sort of pin in it (presumably to let a small amount of coolant/air out from engine side? but not back the other way). The new one does not have this - should it?

 

What you are describing for the old stat is a kind of vent plug, (sorry can't remember the exact name for it - I'm sure someone else will), and I believe it's main function is to allow any trapped air out, (and perhaps to allow water in), as you are attempting to fill the system without airlocks. Somewhat annoyingly newer replacements dont seem to have them, but I believe that the only impact is how difficult it is to get all the coolant in, and all the air out. I think, provided you have managed to do that, it matters not whether it has the hole with the littlre bobble thing through it, or not.

[Ricardo]

I had an old Viva once that airlocked under the stat every time the engine cooled down, because a breather tube was blocked I think, so I drilled a hole in it and it was fine after that.

 

So if there's a wee hole in the original I'd drill one in the new stat or you might have airlock problems.

 

Ric.

[Mr Shifter]

Hi Rob.

I have just read your thread and would like to put my 2 penny worth in .

About 28 ish years ago i used to work for a marine company that used to marinize

the bmc 1.5 engine,we used to get them new direct from the factory in coventry,

now at that time all our engines were indirect cooled (heat exchanger/wet exhaust) for cruisers and

work boats,a boatbuilder in the midlands got in touch with us to see if we could supply one for a narrow

boat,this we did,having no experiance with keel cooling we fitted it with our standard belt driven

jabsco pump,removed the tube stack from the bowman h/exchanger and re-plummed the cooling system.

Now this system worked fine in our factory under test,but in the boat the engine never reached normal working temp,after a lot of going back and forth trying different things,it was found that the problem was the jabsco pump all the time,as the pump is physically pumping the water around the system it is not in the engine long enough to get warm let alone 82 degrees,what we did in the end was to remove the pump and re plum to work on the natural normal thermo siphon system and everythink was oaky dokey.

Now i am not saying that this is your problem but it is worth thinking about.

[alan_fincher]

Hi Rob.

I have just read your thread and would like to put my 2 penny worth in .

About 28 ish years ago i used to work for a marine company that used to marinize

the bmc 1.5 engine,we used to get them new direct from the factory in coventry,

now at that time all our engines were indirect cooled (heat exchanger/wet exhaust) for cruisers and

work boats,a boatbuilder in the midlands got in touch with us to see if we could supply one for a narrow

boat,this we did,having no experiance with keel cooling we fitted it with our standard belt driven

jabsco pump,removed the tube stack from the bowman h/exchanger and re-plummed the cooling system.

Now this system worked fine in our factory under test,but in the boat the engine never reached normal working temp,after a lot of going back and forth trying different things,it was found that the problem was the jabsco pump all the time,as the pump is physically pumping the water around the system it is not in the engine long enough to get warm let alone 82 degrees,what we did in the end was to remove the pump and re plum to work on the natural normal thermo siphon system and everythink was oaky dokey.

Now i am not saying that this is your problem but it is worth thinking about.

Hi Mr Shifter......

 

In fact, I think this one was solved back in early May. If you go back a few posts, you'll see that when the engine was reconditioned, the thermostat had been put in upside-down, so was passing water when it should not have been.

 

I'm interested in your post though, as I'm sure I've seen a similar problem described elsewhere.

 

What happens if you have a Jabsco pump in a closed keel cooling circuit with a thermostat ?

 

I can see you are saying it over-cools, because the Jabsco is pushing the water round so fast.

 

But wouldn't that normally be prevented by the thermostat not opening until operating temperature is reached ?

 

So if there is a thermostat in the circuit, is it simply not effective in holding back the flow against the poiwer available in the Jabsco ?

 

Just curious, that's all!

 

Alan

[Mr Shifter]

Hi Alan

Sorry for digging an old thread up,must have missed the one where they resolved it.

As to you query,we found that the jabsco had enough pressure to force water through the bypass hole in the thermostat and also lifted the normal 7lb pressure cap of it's seat and blow water out of the rad cap overflow.

Now i have seen over the years both 1.5 and 1.8 leyland engines working fine with a jabsco pump,that is why i said that it may not have been his problem,but if you look at most keel cooled engines they do not use a positive pressure pump,but use thermo syphon principal instead,another reason is it takes it's toll on all the rubber hoses and mouldings.

[theclans]

Yes- interesting point about the Jabsco. Now everything is working fine with Thermostat correctly inserted ~(!!), but its true, as soon as the temp hits 80 and the stat opens, I get really rapid cooling down to about 70 and then it goes up again. So yes the Jabsco is probably not really required, but think I'll keep it there just in case...

 

Interesting to have a BMC mariniser adding to the discussion though - who was the company incidently? Think mine was done by "Tempest Diesels"???

[bottle]

Hi

Now just got to sort out the misfiring, diesel in oil, and oil pressure issues but thats another topic altogether.

 

Did you get these sorted or start another thread that I missed.

[Mr Shifter]

Hi There.

If the temp only goes between 70 and 80 degrees then i would not be to duly worried,if it goes any higher then further investigation is needed.

Ah good old Tempest Diesels,remember them well,very good in their day and reliable.

the company i used to work for (14 yrs) was South London based, (CT Marine).

[theclans]

Hi

Did you get these sorted or start another thread that I missed.

 

No, I'm still working on it ! Basically I'm getting erratic oil pressures - thankfully its never low but often on starting its right off the scale (max) and then flickers a lot when underway. Seems to have stabilised a bit after the last filter/oil change. The oil has been diagnosed with containing a lot of diesel, so I also need to check the lift pump. But more likely I think its the result of a bad recon job. Even after the recon the pump timing has been set well advanced and it still smokes. Not good.

 

Think I'll just live with it and run it till it dies!

Edited June 19, 2006 by theclans

[David Schweizer]

No, I'm still working on it ! Basically I'm getting erratic oil pressures - thankfully its never low but often on starting its right off the scale (max) and then flickers a lot when underway. Seems to have stabilised a bit after the last filter/oil change. The oil has been diagnosed with containing a lot of diesel, so I also need to check the lift pump. But more likely I think its the result of a bad recon job. Even after the recon the pump timing has been set well advanced and it still smokes. Not good.

 

Think I'll just live with it and run it till it dies!

Did you have the engine re-conditioned, or just the injection Pump ? Apparently it is quite normal for re-built BMC 1.5 engines to smoke a bit after a re-bore until the rings have bedded in, and this can take quite a while under the light load circumstances experienced by boat engines.

 

I have been told by the Engineer who re-built my engine that the best I could do to run in the engine would be to take the boat for a good hard thrash up the Thames. This has also been the xperience of other people I have met with recently re-bored BMC engines in their boat.

[theclans]

Did you have the engine re-conditioned, or just the injection Pump ? Apparently it is quite normal for re-built BMC 1.5 engines to smoke a bit after a re-bore until the rings have bedded in, and this can take quite a while under the light load circumstances experienced by boat engines.

 

I have been told by the Engineer who re-built my engine that the best I could do to run in the engine would be to take the boat for a good hard thrash up the Thames. This has also been the xperience of other people I have met with recently re-bored BMC engines in their boat.

 

Yes it was a rebore, and its had plenty of thrashings on the Thames (and lengthy canal trips too). The smoke does tend to dissapear when heavily underway on the river, but always comes back. What sort of running time does it normally take to get the rings bedded in?

Still doesnt answer why the pump timing has been overly adjusted though after refitting the engine (advanced as far as possible!!!). Surely this must affect the smoke ? Engine also sounds rough too, and someone told me they thought it was "missing" but I'm not really sure what that sounds like.