BMC 1.5 Diesel Questions

kevinbrown2021

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Hi All.
I need some advice on my engine.

It's a BMC 1.5 Diesel

Was wondereing if anyone knew what the operating temperature should be, and at what point is it classed as overheating.
At the moment it will run all day at 3/4 throttle and sit at 180 degrees, i was told not to push it to full throttle, but i figured it should be able to do it so i tried. when i did the temperature went up to 210 degrees.

is it overheating, or is that within the normal operating temperature?
how do i know if it is overheating? as there is no red mark on the temperature gauge.
I have got the repair manual for this engine but it dosn't give me this infomation.

Thanks
Kevin
 

SimonA

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I dont know the exact temperature. But mine sits at half way on my temp gauge up to about 1800 RPM, then it sits and slightly over half way up to 2200 RPM (top speed).

A while back it kept creeping up much higher and I found the seacock inlet was slightly fouled with weed.
 

alb40

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It should be set to 3000rpm for marine applications, although ex-vehicle engines will go to 4000rpm if they are propped correctly.

In my old boat, mine used to run at about 85oC at any speed upto about 3500rpm. Past that it would rise to about 95oC but didn't seem to get any hotter than that. Max rpm was 3900 for me.

I think the heat exhanger on them (bowman type) is a little undersize for the higher rated ex-vehicle engines. Mine was rated at 40hp @4000rpm. Limiting it to 30hp @3000rpm like thornycrofts did would prevent it being getting too hot.

Mine would run all day at about 3000rpm without trouble. The one time I held it full for a long period, it dropped a combusion chamber insert and smashed a piston, so it would be better not to stress it too much!

Hope that helps

Alex
 

PCUK

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Generally speaking 80--85C is the correct temperature for all heat exchanger cooled engines. My 1.5 wing runs at about 85C at cruising revs (2500rpm). If I open it wide and over-rev beyond 3500rpm (running the main engine at the same time) it goes well over 100C but soon cools when throttled back so I don't do it very often and then for only a couple of minutes to get the boat onto the plane.
 

PCUK

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Raw water cooled means the sea water runs through the block and is also known as direct cooling.
In this case the engine should run at 50-55C to prevent salts caking on the internal water passages due to the heat of normal operation.
Your engine is currently running too hot for raw water cooling and you should get a thermostat for the correct lower temperature.
 

Sgeir

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Plenty of really good advice in the thread, but I wonder if your engine really is raw water cooled, or whether, as I would expect, it draws sea water through a heat exchanger, which in turn cools down the fresh water and coolant that circulate around the engine block. Do you have a metal box with pipes going in and out, with a pressurised radiator cap fitting on the top?

They are great engines and will chug on forever. Two or three points
<ul type="square"> 1 If you do have a heat exchanger I'd suggest that it might be worth running a solution of oxalic acid through it - draw it in fully, stop the engine, and let it settle for a bit. Then thoroughly flush out. This is well worth while for cleaning out all the salts and gunge that may have built up.
2 It's probably not recommended, but also I've done the same with the sealed cooling system, ie around the engine block, taking great care to thoroughly cleanse it with clean fresh water afterwards.
3 Very often these engines were fitted with inadequate seawater pumps so the running temperature can be problematic - my pump was too small and so we deliberately kept the revs down to hold it to 80°-90°C. It should have been running at cooler temperatures and a bigger pump would have helped. [/list]

Until recently I was running exactly the same engine and, even with it running too hot, never had any real problems, except that it was impossible, owing to lack of space in the engine well, to do anything but the most simple maintenance. It had been in the boat since around 1973 and was a bit leaky in the oil department. Not too surprising really - I drove a BMC 15cwt van with the same J2 engine in the early 70s, and there were always oil patches where we parked up.

Then, one day, we found out that there were yachts that didn't have oil in the bilges! /forums/images/graemlins/blush.gif Taking it out and having it reconditioned was an option, but with the cost differences not being great we've opted for fitting a new Beta 37.5 - sea trials hopefully next week.

So, the BMC 1.5 J2 engine has done itself proud, but, a more modern, quieter, cleaner, less bulky, more fuel efficent engine also has its attraction. /forums/images/graemlins/smile.gif
 

alb40

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The engine in carefree is heat exchanger cooled. There will be no salt deposits in it as i fitted a brand new head to it a few years back!

Just don't use it right on full throttle and it wont get hot. It does go any faster with the final 500rpm anyway /forums/images/graemlins/ooo.gif

You could try cleaning the tube stack to help. Didn't make alot of difference but it helps.
 
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