BMC engine oil presure loooow (also which oil)

[Chris Lingwood]

I've finally got my boat moving after goodness knows how long. The engine is a BMC 1.5 which in fact sounds OK, for a 35 year old diesel on solid engine mounts with a gear box hewn from the hills! I'm unimpressed by the oil pressure though. I've only just fitted the gauge so I've no idea what the pressure is normally like (the book suggests 15psi at idle 50psi under load). I get 10-15 at idle, and 20 -25 under load. More worryingly the oil pressure went down to as good as 0 on the gauge at one point, revving it got it back up to 20psi. Would you be worried?

 

It does need an oil change, I've not done it for ages but it's not been used much. What oil would you guys suggest? I can't remember what I put in it last time.

 

I'm intending to (until it's fixed/better)

- change the oil and filter

- clean the gauze on the oil pickup (and clean the sump while it is off)

- check/clean the pressure relief valve

- change the pump I guess (I hope I don't need to get this far)

 

Chris

[cereal tiller]

I've finally got my boat moving after goodness knows how long. The engine is a BMC 1.5 which in fact sounds OK, for a 35 year old diesel on solid engine mounts with a gear box hewn from the hills! I'm unimpressed by the oil pressure though. I've only just fitted the gauge so I've no idea what the pressure is normally like (the book suggests 15psi at idle 50psi under load). I get 10-15 at idle, and 20 -25 under load. More worryingly the oil pressure went down to as good as 0 on the gauge at one point, revving it got it back up to 20psi. Would you be worried?

 

It does need an oil change, I've not done it for ages but it's not been used much. What oil would you guys suggest? I can't remember what I put in it last time.

 

I'm intending to (until it's fixed/better)

- change the oil and filter

- clean the gauze on the oil pickup (and clean the sump while it is off)

- check/clean the pressure relief valve

- change the pump I guess (I hope I don't need to get this far)

 

Chris

[Tony Brooks]

I've finally got my boat moving after goodness knows how long. The engine is a BMC 1.5 which in fact sounds OK, for a 35 year old diesel on solid engine mounts with a gear box hewn from the hills! I'm unimpressed by the oil pressure though. I've only just fitted the gauge so I've no idea what the pressure is normally like (the book suggests 15psi at idle 50psi under load). I get 10-15 at idle, and 20 -25 under load. More worryingly the oil pressure went down to as good as 0 on the gauge at one point, revving it got it back up to 20psi. Would you be worried?

 

It does need an oil change, I've not done it for ages but it's not been used much. What oil would you guys suggest? I can't remember what I put in it last time.

 

I'm intending to (until it's fixed/better)

- change the oil and filter

- clean the gauze on the oil pickup (and clean the sump while it is off)

- check/clean the pressure relief valve

- change the pump I guess (I hope I don't need to get this far)

 

Chris

 

If its an electrical gauge it is probably telling porkies so the first thing I would do is to beg, borrow, or hire a mechanical gauge that screws into the sender hole and check the actual oil pressure.

 

AS you have 15psi on idle (assuming you still have it when hot) then its not likely to be the relief valve.

 

In this case I think I would give it a good flush with flushing oil before changing the filter - perhaps two or three goes because it might be the gauze strainer, but I favour the sender unit at present.

[Thewatchmaker]

I've finally got my boat moving after goodness knows how long. The engine is a BMC 1.5 which in fact sounds OK, for a 35 year old diesel on solid engine mounts with a gear box hewn from the hills! I'm unimpressed by the oil pressure though. I've only just fitted the gauge so I've no idea what the pressure is normally like (the book suggests 15psi at idle 50psi under load). I get 10-15 at idle, and 20 -25 under load. More worryingly the oil pressure went down to as good as 0 on the gauge at one point, revving it got it back up to 20psi. Would you be worried?

 

It does need an oil change, I've not done it for ages but it's not been used much. What oil would you guys suggest? I can't remember what I put in it last time.

 

I'm intending to (until it's fixed/better)

- change the oil and filter

- clean the gauze on the oil pickup (and clean the sump while it is off)

- check/clean the pressure relief valve

- change the pump I guess (I hope I don't need to get this far)

 

Chris

 

I had a similar issue with my BMC 1.8

Gauge and sender were either mismatched or faulty giving a reading of 15psi at tickover and 35 under load.

Connect a 'Smiths' capillary gauge up to it preferable one you know to be accurate.

Plenty on eBay but avoid ones with stuck needles!

I think if your oil pressure was genuinely as low as your gauge is showing there would be some other symptoms showing by now.

[nb Innisfree]

Our LPWS4 has indicated low pressure from new, I guessed it was the gauge not matched to the sender so carried on and it's now done 3000+ hours and still runs like a well oiled watch.

 

I will get round to checking it properly one day, honest.

[Chalky]

 

In this case I think I would give it a good flush with flushing oil before changing the filter - perhaps two or three goes because it might be the gauze strainer, but I favour the sender unit at present.

 

Don't over do it. On older engines the dirt is often what holds the oil in!

My first thoughts would also be the sender. Next I'd try changing the oil and filter (check you've got the right one - if its wrong it'd affect pressure).

If it's got a lot of hours on it it might be the main bearings. I had this on an MGB (1.8 B series) - no bearing noise but low oil pressure on tickover (70 psi running, 15 psi tickover). I changed the main bearings (1 day work in a car ) & left the crank alone and pressure went up to 50psi on tickover. The B used 20/50 oil and there was a noticeable difference in pressure between a hot and cold engine.

[Tony Brooks]

Don't over do it. On older engines the dirt is often what holds the oil in!

My first thoughts would also be the sender. Next I'd try changing the oil and filter (check you've got the right one - if its wrong it'd affect pressure).

If it's got a lot of hours on it it might be the main bearings. I had this on an MGB (1.8 B series) - no bearing noise but low oil pressure on tickover (70 psi running, 15 psi tickover). I changed the main bearings (1 day work in a car ) & left the crank alone and pressure went up to 50psi on tickover. The B used 20/50 oil and there was a noticeable difference in pressure between a hot and cold engine.

 

I would never normally advocate using flushing oil but I have also seen old BMCs with badly fouled strainers so trying to juggle the lesser of two evils I think a good flush may be worth while if the sender and gauge are telling the truth. Unfortunately so many of these older engines are full of muck and I would hate to soften but not remove the muck so the new oil brings it off and blocks the filter (no one will know because the pressure differential bypass will open and send unfiltered oil to the engine).

[Chris Lingwood]

I really really don't want to change the main bearings. I've already got a mgb engine that needs rebuilding....and a scimitar which needs a new gear box......

 

The sender and the gauge are definitely matched (I bought them at the same time), that doesn't mean that it's not just wrong though. It is an inexpensive electrical one. I've got a smiths one in my mg but I'd rather not take it out, those capillaries are easy to break.

 

The 15psi on idle was cold, the 0 was hot, not that it stayed that low, but it was definitely lower when hot 10ish I think.

 

I have no idea about hours, the previous owner found the gauges in the bilge and promptly binned them. Its old. People do comment on how not terrible it sounds for a b series diesel though.

 

I don't like the idea of flushing either. This engine hasn't got any leaks on it at the moment, I'm not sure I want to tempt fate. And it is almost certainly full of crud. I'd rather take the sump off and clean that first, then consider a flush.

 

It needs an oil change first so I'll do that with some cheap 20w50, it's probably not going to stay in there long. See what happens.

[Chris Lingwood]

I've also just ordered a mechanical gauge. If it gives me answers I prefer I'll put that in the instrument panel.

[sociable_hermit]

I really really don't want to change the main bearings. I've already got a mgb engine that needs rebuilding....and a scimitar which needs a new gear box......

V6 MGB. Job done

[Chalky]

V6 MGB. Job done

I've got an 80kW inverter sitting on my desk and I've seen a very nice 50kW induction motor to replace the B-series with. Just need to find a cheap 300V battery.

Electric MGB - full torque from 0 rpm. Very quick until either the battery goes flat or the plug comes out of the wall

[RobinJ]

I would never normally advocate using flushing oil but I have also seen old BMCs with badly fouled strainers so trying to juggle the lesser of two evils I think a good flush may be worth while if the sender and gauge are telling the truth. Unfortunately so many of these older engines are full of muck and I would hate to soften but not remove the muck so the new oil brings it off and blocks the filter (no one will know because the pressure differential bypass will open and send unfiltered oil to the engine).

I agree, especially with an engine that has been stood, got flooded or hasn't had an oil change since whenever, as the alternative is to strip them down.

 

But the other thing which I have never understood is the variation with pressure readings, I suspect it depends where the gauge is attached! Some regularly sit on 25psi and never move, others read 80 and drop to 40 or 50, I think it is related to whetehr the gauge is on the high pressure or low pressure side (of the relief valve).

 

The other point, what is the dipstick like?

If the gauge is dropping to 0, it is possibly running out of oil, so the level may be low. Revving up can help to flush the oil through and suck up more, so this may indicate that the oilways are a bit clogged?

[Chris Lingwood]

The level is fine, the oil is very black (it is a diesel) but fairly runny.

 

Can't rule out clogging, can you ever?

 

A friend of mine suggested I might just have diluted the oil a bit by flooding it, I was having trouble starting it, but it was heater problems (they weren't actually connected!).

Edited April 18, 2011 by Chris Lingwood

[RobinJ]

The level is fine, the oil is very black (it is a diesel) but fairly runny.

 

Can't rule out clogging, can you ever?

 

A friend of mine suggested I might just have diluted the oil a bit by flooding it, I was having trouble starting it, but it was heater problems (they weren't actually connected!).

Can't see you getting much fuel past the rings just by turning it over and chances are that when its fired up and warm, it will be recycled!

You can run these engines on some of the newer oils, but they seem expensive considering most of the additives are not going to do anything in a BMC?

Mine was never run on anything except HD30, but if you are experiencing a range of temperatures and conditions, a multigrade may help.

It is increasingly difficult to find API CC oils, but there are still a few out there!