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BWM

Oil pressure question

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I changed the oil and filter on the RN in my son's new boat over the weekend, the previous owner had used Halfords classic motor oil which is designed for petrol engines and is 15/40. The oil I put in is the recommended SAE 30, and also replaced the existing Fram/Coopers ft4777/LSF5104  with a Coopers LSF5104. 

  Before I changed them the pressure showed 60 psi cold and 20 psi hot, afterwards, with the new oil/filter the guage shows 40 psi cold and 14 psi hot - any idea why this would be, and should I be concerned?

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A correction to the above.

Halfords Classic Motor oil is rated both API-SE, so for "Spark" (Petrol) ignition, and API-CC, so for "Compression" (Diesel) ignition.

I would have no qualms whatsoever about using it in a narrow boat's diesel engine, if a grade of 20W/50 is suitable in that engine.

 

(This is no different to say the highly recommended Morris "Golden Film" oils, which are eqally OK for petrol and diesel).

However I note you say that SAE 30 is recommended by RN.

I have in the past experimented with using SAE 30 versus SAE 20W/50 in several of my engines, including in Flamingo's before it had a major rebuild.  Flamingo used to fall to quite low pressures when fully hot, (happily now fully cured), but I did not find the kind of massive differences in pressures between the different oils that you are reporting- I wouldn't expect that. However that was an air-cooled Lister not an RN, so a different beast.

 

You don't say at what revs you are seeing " 40 psi cold and 14 psi hot ".  Can you clarify that please.  I don't know RNs, but if I were seeing 14 psi hot on tick-over I doubt I'd be concerned.  However if however I was only getting 14 psi at full lick, I think I'd want to be understanding why.

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Switching from a multigrade to the recommended oil must be a good thing!!!The change in oil pressure is what I would expect,the ratio of hot pressure to cold pressure is consistent at 1 to 3=20 to 60,14 to40 .Any body disagree??😎😎

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29 minutes ago, Ian F B said:

Switching from a multigrade to the recommended oil must be a good thing!!!The change in oil pressure is what I would expect,the ratio of hot pressure to cold pressure is consistent at 1 to 3=20 to 60,14 to40 .Any body disagree??😎😎


No, I'm not following why you would expect the ratio to remain the same.

When cold the SAE 20W/50 should have been acting as an SAE 20.  That is thinner than the SAE 30 that has replaced it.  So if the SAE 30 is thicker than the multi-grade should behave in a cold engine, why should the cold oil pressure have fallen from 60 psi to 40 psi?   At the very least I would have expected it to stay the same.  (Perhaps not increase, particularly if a bypass valve is opening to stop oil pressure exceeding 60 psi).

I can see, however, why the pressure in a hot engine may be less with the SAE 30 than the multi-grade.  The latter should have been behaving as SAE 50, a much thicker oil, so the pressure might be significantly less, (as is being observed).

Can you explain why switching from an oil that should only have acted as SAE 20 when cold, to a thicker SAE 30 one should possibly reduce the cold oil pressure?  At the moment I can't, but perhaps I've missed something obvious.

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46 minutes ago, alan_fincher said:

A correction to the above.

Halfords Classic Motor oil is rated both API-SE, so for "Spark" (Petrol) ignition, and API-CC, so for "Compression" (Diesel) ignition.

I would have no qualms whatsoever about using it in a narrow boat's diesel engine, if a grade of 20W/50 is suitable in that engine.

 

(This is no different to say the highly recommended Morris "Golden Film" oils, which are eqally OK for petrol and diesel).

However I note you say that SAE 30 is recommended by RN.

I have in the past experimented with using SAE 30 versus SAE 20W/50 in several of my engines, including in Flamingo's before it had a major rebuild.  Flamingo used to fall to quite low pressures when fully hot, (happily now fully cured), but I did not find the kind of massive differences in pressures between the different oils that you are reporting- I wouldn't expect that. However that was an air-cooled Lister not an RN, so a different beast.

 

You don't say at what revs you are seeing " 40 psi cold and 14 psi hot ".  Can you clarify that please.  I don't know RNs, but if I were seeing 14 psi hot on tick-over I doubt I'd be concerned.  However if however I was only getting 14 psi at full lick, I think I'd want to be understanding why.

These pressures were taken near the lower end of the rpm range, a detail I should have included. I didn't check the full specs of the Halfords oil but it stated petrol only, on the website I believe. 

  14 psi is normal at full temperature on my Jp3, starting at 25 psi cold. I'd read some other threads on here suggesting 35 psi hot was normal for these engines but wether the age of this one has any bearing on that (circa 1940), I don't know. 

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I have always used Morris Gold Film 30s in my RN as did the only other owner of the boat with no problem. It runs at the same pressure as you mention at tick over when cold and hot. Pressure jumps back up when running at normal revs 'about 600RPM' even when hot. I've never had a problem and the engine has been in the boat for over thirty years. 

 

If you haven't done so already I would recommend joining the RN register, there forum is a great place for gleaning information and there are some useful workshops and discussion at their annual rally. 

Edited by captain birdseye

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23 minutes ago, captain birdseye said:

I have always used Morris Gold Film 30s in my RN as did the only other owner of the boat with no problem. It runs at the same pressure as you mention at tick over when cold and hot. Pressure jumps back up when running at normal revs 'about 600RPM' even when hot. I've never had a problem and the engine has been in the boat for over thirty years. 

 

If you haven't done so already I would recommend joining the RN register, there forum is a great place for gleaning information and there are some useful workshops and discussion at their annual rally. 

Thanks, when you say it runs at the same pressures, is that the 40/41psi? The pressure rises with increased rpm but I generally take tickover as a baseline. I did take your suggestion from a previous thread and told my son to join the register. 

  When changing the oil on my Jp3 I generally take the side cover off the block which allows me to clean out the old oil completely along with any combustion deposits (it has the marine dry sump), is there any similar access on an RN? Without doing This, the oil tends to blacken up immediately due to what little is left behind. 

Edited by BWM

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1 hour ago, BWM said:

I didn't check the full specs of the Halfords oil but it stated petrol only, on the website I believe.

Is it this one?

 

If so it is rated API  SE CC.

The CC bit means it is sited for diesels.

 

(I'm not saying it's the right oil for your RN, y the way, because it seems that should be a monograde not a multi-grade, but I'd be happy to use it in anything needing a 20W-50.)

1 hour ago, BWM said:

These pressures were taken near the lower end of the rpm range, a detail I should have included.

What pressure are you now seeing when at "cruising", (not past moored boats!) RPM, (cold and hot)?

Edited by alan_fincher

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36 minutes ago, BWM said:

Thanks, when you say it runs at the same pressures, is that the 40/41psi? The pressure rises with increased rpm but I generally take tickover as a baseline. I did take your suggestion from a previous thread and told my son to join the register. 

  When changing the oil on my Jp3 I generally take the side cover off the block which allows me to clean out the old oil completely along with any combustion deposits (it has the marine dry sump), is there any similar access on an RN? Without doing This, the oil tends to blacken up immediately due to what little is left behind. 

Usually the pressure is slightly over 40PSI at tickover when the engine is cold but doesn't rise much when revs are increased, when the engine is hot pressure drops at tickover but rises again when the engine is running at what for me is normal cruising speed of 600 - 650 RPM. 

 

I've never took the side cover off my engine but you can remove it (RH side ) but I'm not that sure how easy it would be to do. I'm afraid I'm not much of a engine man, I just do the normal maintenance and ring up Ian Crompton if I need any help, which thankfully doesn't happen very often.

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10 minutes ago, alan_fincher said:

Is it this one?

 

If so it is rated API  SE CC.

The CC bit means it is sited for diesels.

 

(I'm not saying it's the right oil for your RN, y the way, because it seems that should be a monograde not a multi-grade, but I'd be happy to use it in anything needing a 20W-50.)

What pressure are you now seeing when at "cruising", (not past moored boats!) RPM, (cold and hot)?

Yes, that's the one. In the drop down specification it does say petrol only but I take your point. 

  At mid range rpm it registers 35ish. 

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9 minutes ago, BWM said:

Yes, that's the one. In the drop down specification it does say petrol only but I take your point. 

  At mid range rpm it registers 35ish. 

That sounds about right when the engine is hot.

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12 minutes ago, BWM said:

  At mid range rpm it registers 35ish. 

I don't think that would scare me, but I dont know RNs.

What I can't get my brain around us why you should have seen a big reduction in the low revs COLD oil pressure when switching from a multi-grade to a monograde.  That makes no sense to me, so I wonder if anybody can give a plausible explanation.

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44 minutes ago, alan_fincher said:

I don't think that would scare me, but I dont know RNs.

What I can't get my brain around us why you should have seen a big reduction in the low revs COLD oil pressure when switching from a multi-grade to a monograde.  That makes no sense to me, so I wonder if anybody can give a plausible explanation.

Likewise, I have no idea. I assume the filter whilst not an exact duplicate wouldn't cause it? In size, visual appearance both inside and out, it is the same. 

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mine is running sae 30 cold first start runs at around 30-40psi after 5 mins it slowly drops down to about 10-15psi it then sits at that all day, dosnt matter if it's running saw or thermostats raw.

 

when I got mine it nearly made 15 cold and bounced like mad from 0-10 hot. I compleatly flushed it by my mistake at over 80+psi and I had cleared out all the gunk and build up from sump. after my mistake (tried to remove the old filter not realising it had the pressure control in it) and did another oil change its ran at the 30-40 & 10-15 ever sence. this was a rebuild engine (was told in 2008) but it's still got alot of proper national parts in.

 

yours sounds about right but the wrong oil could have put slight wear into parts as the tolerance would have been diffrent.

if really concerned check with Bob tidy he has helped me alot!

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On 19/11/2018 at 11:25, alan_fincher said:

I don't think that would scare me, but I dont know RNs.

What I can't get my brain around us why you should have seen a big reduction in the low revs COLD oil pressure when switching from a multi-grade to a monograde.  That makes no sense to me, so I wonder if anybody can give a plausible explanation.

I suppose that it is possible that either a: the old oil filter was a 20 micron element and the new one is 30 micron or bigger or b: that a bit of carbon / debris/ fluff etc has been displaced and is affecting the pressure relief valve so that it is leaking back a little. Assuming of course that the oil pressure gauge is working correctly.

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it will more than likely be down to the oil. 1 is thicker than the other.

 

i could go into the way oil works ect but the basics are a twin number say 5w 30 is an sae 30 oil at temp but has a cold start properly of sae 5 at low (it's thin when cold and dosnt go as solid cold) but a high number after works better and dosnt deteriorate at higher temps but is a slightly thicker oil. it's not the best way to describe it but it's a semi basic idea.

 

this dosnt mean a twin number is better or worse its all down to engine tolerances and materials. how quick they heat up and expand ect ECT

 

an old engine or design dosnt have the oil ways or lube design of a modern engine. you would prob find an old engine on 5w30 or 5w40 would prob not have the lube it needed on cold start due to the oil feed design and metals inside.

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16 hours ago, steamraiser2 said:

I suppose that it is possible that either a: the old oil filter was a 20 micron element and the new one is 30 micron or bigger or b: that a bit of carbon / debris/ fluff etc has been displaced and is affecting the pressure relief valve so that it is leaking back a little. Assuming of course that the oil pressure gauge is working correctly.

 

8 hours ago, billybobbooth said:

it will more than likely be down to the oil. 1 is thicker than the other.

 

i could go into the way oil works ect but the basics are a twin number say 5w 30 is an sae 30 oil at temp but has a cold start properly of sae 5 at low (it's thin when cold and dosnt go as solid cold) but a high number after works better and dosnt deteriorate at higher temps but is a slightly thicker oil. it's not the best way to describe it but it's a semi basic idea.

 

this dosnt mean a twin number is better or worse its all down to engine tolerances and materials. how quick they heat up and expand ect ECT

 

an old engine or design dosnt have the oil ways or lube design of a modern engine. you would prob find an old engine on 5w30 or 5w40 would prob not have the lube it needed on cold start due to the oil feed design and metals inside.

Thanks, interesting theories and food for thought. 

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