Warm starting problem

[Colin North]

Hi,

I have a hot start problem.

Cold starting has not been a problem - Glowplugs for 30 seconds, throttle out of gear and set to about 2/3 way up, twist key to start - starts within about 1 second, pull throttle back to fast tickover - great. It will happily run for as long as required. All very well tempered. No hesitation on acceleration, deceleration or idling. I would say it is pretty good for a 1980 BMC 1.5 diesel. The engine is water cooled, feeding a calorifier with all temperatures looking absolutely normal. In the unlikely event of the thermostat opening there is a swim cooler. I generally cruise slowly and have not been on rivers with flow. The fuel filter is a screw-on disposable (adapted from the CAV type) and does not leak, the fuel system seems to be in good order.

 

Most times the engine is only run once per day either to charge batteries or to move, so no problems, but...

 

We have just been on holiday and on two occasions decided to stop for lunch after about two hours of engine run time. After an hour or so of being stopped attempts to start the engine fail. It is as if there is no fuel.

The 'STOP' is pushed fully home, the glow plugs are OK etc. There is no white smoke from the exhaust. Releasing the injector connectors shows immediate fuel 'sputs'.

After a FULL bleed of the diesel system and a lot of cranking eventually it starts and then behaves perfectly for the rest of the day.

Any cold starts after this time are perfect.

Any suggestions please.

[Darren72]

Hi,

I have a hot start problem.

Cold starting has not been a problem - Glowplugs for 30 seconds, throttle out of gear and set to about 2/3 way up, twist key to start - starts within about 1 second, pull throttle back to fast tickover - great. It will happily run for as long as required. All very well tempered. No hesitation on acceleration, deceleration or idling. I would say it is pretty good for a 1980 BMC 1.5 diesel. The engine is water cooled, feeding a calorifier with all temperatures looking absolutely normal. In the unlikely event of the thermostat opening there is a swim cooler. I generally cruise slowly and have not been on rivers with flow. The fuel filter is a screw-on disposable (adapted from the CAV type) and does not leak, the fuel system seems to be in good order.

 

Most times the engine is only run once per day either to charge batteries or to move, so no problems, but...

 

We have just been on holiday and on two occasions decided to stop for lunch after about two hours of engine run time. After an hour or so of being stopped attempts to start the engine fail. It is as if there is no fuel.

The 'STOP' is pushed fully home, the glow plugs are OK etc. There is no white smoke from the exhaust. Releasing the injector connectors shows immediate fuel 'sputs'.

After a FULL bleed of the diesel system and a lot of cranking eventually it starts and then behaves perfectly for the rest of the day.

Any cold starts after this time are perfect.

Any suggestions please.

Sorry no idea, but as a fellow 1.5 owner I wait with you to find the answer. Wheres Tony Brookes when you need him!

[Geoff Taylor]

Hi,This is a bit of a strange problem, check that the stop lever on the injector pump is returning fully home after pushing in stop control (I guess it is cable operated). If the stop lever is sticking slightly you will get fuel showing at injectors but insufficient to start engine,do you find air when bleeding?,hope this helps.

[Tony Brooks]

Hi,This is a bit of a strange problem, check that the stop lever on the injector pump is returning fully home after pushing in stop control (I guess it is cable operated). If the stop lever is sticking slightly you will get fuel showing at injectors but insufficient to start engine,do you find air when bleeding?,hope this helps.

 

 

I agree.

 

I wonder if there is some water in the fuel and it is gumming up the governor. If you do have water in the fuel the hydraulic governors can do odd things. If you are bleeding from the bleed screw on top of the pump (as opposed to the one on the body) the as it vents from above the governor I think it could shift water droplets but you should see it has just spat out water if looking carefully.

 

I definitely think drawing some liquid from the bottom of the tank would be a good idea. Also every time you remove the filter empty it into a tray so you can get some idea of what it has caught.

 

Sorry no idea, but as a fellow 1.5 owner I wait with you to find the answer. Wheres Tony Brookes when you need him!

 

 

Only an email away.

 

Son has just bought a neglected house so am very busy with removing fire places, plastering and crack repairing at the moment - then I am trying to get the next lot of Q&As away for the magazine. Not much time for browsing the forum.

[Chalky]

If it carries on doing it get the compressions checked. I had an MG that would start when cold but not when hot. Tried everything - the fault turned out to be head gasket that was sealing ok when cold but not when hot.

[Phil Ambrose]

If it carries on doing it get the compressions checked. I had an MG that would start when cold but not when hot. Tried everything - the fault turned out to be head gasket that was sealing ok when cold but not when hot.

 

This kinda makes sense, would I be right in thinking that oil may be present in header or water in the oil (grey scum on oil filler cap) if this is the case.

 

Phil

[Chalky]

This kinda makes sense, would I be right in thinking that oil may be present in header or water in the oil (grey scum on oil filler cap) if this is the case.

 

Phil

 

Depends on where it's blown. If it's into an oil gallery and the water jacket then you may get that. My 1.8 B series petrol (40 thou overbore - 1840cc, big valve stage 2 head 9.75:1, 272 cam etc) blew between cylinders so no contamination. On another occasion I also had a blow between a combustion chamber and the water jacket. This pressurised the cooling system, but no water in the oil.

[Phil Ambrose]

Depends on where it's blown. If it's into an oil gallery and the water jacket then you may get that. My 1.8 B series petrol (40 thou overbore - 1840cc, big valve stage 2 head 9.75:1, 272 cam etc) blew between cylinders so no contamination. On another occasion I also had a blow between a combustion chamber and the water jacket. This pressurised the cooling system, but no water in the oil.

 

True but still worth considering.

 

Phil

[Colin North]

Thank you all for your input.

 

There are no signs within the water system of any oil, similarly no oil emulsion in the rocker box. No other sings of illness at all.

 

Is it possible that compression can be different between a hot engine and a cold engine?

Does compression rely on cold oil in the bore/piston rings to make a perfect seal?

Could it be that the bores are slack enough that with a cold engine and cold oil makes a seal and gives good compression but when 'hot'the bore has expanded, the oil is thinner? I think the oil is a 10/40 for common diesels.

 

Colin

[BEngo]

Thank you all for your input.

 

 

 

Is it possible that compression can be different between a hot engine and a cold engine?

Does compression rely on cold oil in the bore/piston rings to make a perfect seal?

Could it be that the bores are slack enough that with a cold engine and cold oil makes a seal and gives good compression but when 'hot'the bore has expanded, the oil is thinner? I think the oil is a 10/40 for common diesels.

 

Colin

 

The answers to your question are Yes, No and No.

 

A hot engine usually has better compression than a cold one.

 

The starting issue is getting the air hot enough to ignite the fuel. The compression temperature achieved is governed by the temperature at the start and the compression ratio. There are some worked examples in Chapman's "The Modern High-Speed Oil Engine" for anyone who wants the detail, but realistically any loss of compression through warm oil is going to be more than balanced by the increased starting temperature of air that is in a warm engine and continuing to receive heat from the warm cylinder walls.,

 

Additionally, the piston is designed so that as it warms up the fit improves ( Aluminium alloy expands more than cast iron), hence tyhe disappearance ( or reduction ) of piston slap once the engine warms up.

 

The compression rings seal against the piston lands at the bottom of the land and this is a near metal-to metal seal. There should be very little oil up there,if the oil control rings are working properly, because otherwise the oil will partly burn during the power stroke and clog the rings up. There will also be excessive smoke.

 

I think that (at UK temperatures) the BMC 1.5 uses either a monograde SAE30 oil or a 20W50 multigrade, to API CC in either case, but using a 10W40 is not likely to give the start problems you have.

 

N

[STUBAG]

If it carries on doing it get the compressions checked. I had an MG that would start when cold but not when hot. Tried everything - the fault turned out to be head gasket that was sealing ok when cold but not when hot.

......and are the valve clearances correct? Too tight, and the valves won't close when hot. Worth a quick look, won't take too much dismantling. Good luck.