Oil pressure drops when engine gets warm.

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Galimor_001
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Oil pressure drops when engine gets warm.

Post by Galimor_001 » Thu Aug 08, 2019 3:18 pm

Hello there!
I'm new to Dnepr life after working on my MT10-36 for 2 years, and upgrading to an external oil filter fitted to the front cover. The problem I'm now having is that the oil pressure drops when the engine and the oil gets hot.
I'm running 20w50 oil and then the pressure at cold is about 40 psi at idle and 65 psi when giving some gas. This drops to 20 psi at idle and cruising and maybe goes up to 35-40 psi when revving it.
What could be causing it? And is it cause for concern?

Any advice is appreciated!

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Re: Oil pressure drops when engine gets warm.

Post by windmill » Thu Aug 08, 2019 3:29 pm

I have no experience with a Dnepr, but that's about what I'd expect to see on any vehicle.
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Re: Oil pressure drops when engine gets warm.

Post by rivers » Thu Aug 08, 2019 3:37 pm

Normal on any motor for the pressure to drop when the oil gets hot and thins out.
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Re: Oil pressure drops when engine gets warm.

Post by sKiZo » Thu Aug 08, 2019 3:57 pm

Yup - that's probably why they don't put oil pressure gauges on machines anymore. My Olds Aurora (Northstar) starts cold at around 90 pounds and will drop to 13 or thereabouts on hot idle ... pretty good swing that sounds a bit scary, but just as the factory built em ...

If you weren't getting a similar drop with the old filter setup, chances are good you had a plugged element or some such that wasn't allowing the pressure to drop as it should?
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Re: Oil pressure drops when engine gets warm.

Post by Mr Wazzock » Thu Aug 08, 2019 4:39 pm

One very hot August Bank Holiday in atrociously congested traffic my 850 Guzzi's oil warning light lit up every time I stopped and let it idle :lol:
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Re: Oil pressure drops when engine gets warm.

Post by Galimor_001 » Thu Aug 08, 2019 5:02 pm

From what I've read so far though Dnepr engines run on quite high pressures, anything higher than 40 psi when hot is acceptable hence why I'm making this thread.

I can't switch back to the old setup either, as I broke the flywheel and crankshaft last summer the first time we renovated the engine, but didn't tighten the flywheel not tight enough and the other clutch plate got caught on the gearbox and seized up good.

What I'm guessing it is is either a weak oil pump or busted oil pressure relish valve, but I'd like advice from people that have worked on Dneprs longer than I've been alive, preferably.

Thanks for your replies though.

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Re: Oil pressure drops when engine gets warm.

Post by RC20 » Thu Aug 08, 2019 8:39 pm

What Mfg and sub type oil?

I don't know if this helps but on our Diesel generator engine, oil warning was 20 psi

Shutdown was 10. A diesel engine has vastly more heavy loading that your machine will. My F250 has a fake analog gauge that does not go to zero until it hits 10.

Generator of that size runs 1800 RPM. Had to do some special stuff to get to idle.

That kind of pressure in an old style engine is plenty good.
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Re: Oil pressure drops when engine gets warm.

Post by Galimor_001 » Fri Aug 09, 2019 6:50 am

RC20 wrote:
Thu Aug 08, 2019 8:39 pm
What Mfg and sub type oil?
It's a swedish brand, Biltema.
Mineral oil with spec API SJ/CF, dunno if that tells you anything.

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Re: Oil pressure drops when engine gets warm.

Post by Claus » Fri Aug 09, 2019 7:10 am

Galimor_001 wrote:
Thu Aug 08, 2019 3:18 pm

I'm running 20w50 oil and then the pressure at cold is about 40 psi at idle and 65 psi when giving some gas. This drops to 20 psi at idle and cruising and maybe goes up to 35-40 psi when revving it.
I thinks that´s normal because the viscosity of the oil drops when warm.
40 psi at idle cold and 20 psi hot at idle is ok on Dnepr. The warning lamp comes on at 0,42 bar (6 psi). So everything above 10 psi in idle is safe.
40 psi at revs when hot is close to what Dnepr wants ist to be (3 bar= 43,51 psi) and safe as well.

What happens sometimes is that the centrifuge housing cracks when the central bolt is tightened up too hard or when wrong gaskets have been used. This results in a sudden loss of oil pressure.
When oil pressure is too low (oil lamp comes on in idle every time), most of the times the big end bearings are worn out. But in your case that doesn´t seem to be the case. Don´t worry about.
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Re: Oil pressure drops when engine gets warm.

Post by Galimor_001 » Sat Aug 10, 2019 9:50 am

Claus wrote:
Fri Aug 09, 2019 7:10 am

40 psi at revs when hot is close to what Dnepr wants ist to be (3 bar= 43,51 psi) and safe as well.

Don´t worry about.
Thanks, that puts my anxiety somewhat to rest. I'll drive around a while and drive in the new components before complaining again:P

Thank you all for your replies though, I'll be sure to return if anything else comes up :)

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Re: Oil pressure drops when engine gets warm.

Post by RC20 » Mon Aug 12, 2019 7:28 pm

It's a swedish brand, Biltema.
Mineral oil with spec API SJ/CF, dunno if that tells you anything.
Yes it does. I won't recommend synthetic but its an option if you run it in the cold. More along let sleeping dogs lie.

It should have a weight number on it as well, 20W-50 (European may express it differently)

https://www.biltema.se/en-se/car---mc/c ... 2000022963 :?:

With mineral oil you are in the vagaries of temperature and the to number is important. Down to about 5C then you need to shift to lighter mineral. If that i s the oil they say -10C but that is like honey until it warms up

Less so with Synthetic that does not break down, but you can get a lot of crud out an an engine in a switch and upset the happy apple cart.
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