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... another oil pressure thread


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Hello people. Not sure if I'm getting paranoid here but anyway, as my therapists I'd appreciate getting something off my chest.

 

Last year I took photos of my oil pressure gauge at idle, 2k and 2.5k. The readings were about 25 (can't see the 2 because hidden by needle), 50 and just over 50 respectively.... nothing to worry about thinks I.

 

Over the last few months I think I've detected different pressures (slightly dropping) from last year. <_<

 

Today, engine hot, readings are around 20 (can now easily see the 2), slightly less than 50, and 50..... anything to worry about here?? Engine feels as before and no different, not loosing any engine oil (same oil as last year), temp is between 1/4 to 1/2, acceleration is strong.

 

Now I know when oil is cold, pressure is high. So if engine hot, pressure is low. Therefore am I just detecting the difference in oil temp?? When oil ages does it loose pressure :unsure: ?? My engine oil has probably done around 2000 miles. Should I be changing at 3k or 6k miles? Oil currently used is Miller Classic. What pressure is too low? I've read on here that 15psi is ok at idle and between 40-60 psi at 2k is also ok. Do we all still hold to that?

 

Cheers and thanks for listening.

 

Dave

 

 

 

 

 

 

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Dave

Good morning

 

I will try to offer what little I know or understand;

When the engine is hot, the oil will thin and the viscosity (the measure of the oils ability to flow) will drop.

 

As a reference, the viscosity of water is 1 centistoke (cst) at 40°C.

Engine oil viscosity varies, but is generally between 150cst and 500cst, again at 40°C

 

A lower (not low) pressure reading is normal, when the engine is hot.

 

At this point, I should dispel a basic myth regarding flow and pressure.

The pump in a fluid system delivers flow only.

Pressure is generated by the resistance of the system components to the flow

The pump pressure rating is it's maximum ability to deliver flow in the face of the resistance generated

 

(Think of a garden hose. When you put your thumb over the end of the open hose, you restrict the ability of the fluid to flow, as a result the pressure increases and flow rate increases, so as to get the same volume of fluid through the smaller hole created when you placed your thumb over the hose end)

 

When oil ages, it is the additive package that will deteriorate first and it is the additives that protect the engine as much as the base oil.

 

Given that you have not maltreated the oil (allowed water / over heated) 2000 miles is not an issue.

I change the oil in my 6 annually, irrespective of mileage, just because that is my preference

I would change at 5000 miles as a maximum, it will do no harm and will ensure your engine is best protected

 

As for pressure (and this is only my personal opinion) I would worry at;

- idle, hot, oil pressure below 20psi

- hot engine at 2000rpm pressure of 40psi or below

 

I hope that this helps

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Hi Dave,

I wouldn't panic over your problem.

 

If you want to investigate further why not do an oil/filter change and use either a cheaper oil (Halfords works well) or another brand - Penrite etc or different grade.

 

This may reveal information to stop your worrying.

 

Roger

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Dave

 

Should have included this, in case you are not familiar with Cst

 

http://www.bobistheoilguy.com/viscosity-charts/

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Hi Dave,

 

back in the day the requirement was to change oil every 6K miles or 6 months, whichever came first . . . . .

 

Oil quality is better now than then, but it's still oil - and it's classic mineral oil, not modern synthetic stuff, and the car isn't in daily use.

 

Last year's oil is history, Change it.

 

Cheers

 

Alec

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Thanks all. I've read through Bobistheoilguy thread. Not sure whether I understand precisely what he is banging on about but two things did spring out..... 10psi for every 1k revs apparently ok :unsure: and thin oil is better than thick.

 

So to conclude this thread, I'm off to put the 20w60 penrite classic triumph oil into my car (to replace the thinner 20w50 already in there) before it goes off and turns waxy from being stored on my garage shelf over the winter :ph34r:

 

Oh yeah... and I'm probably not going to worry over the oil pressure reading at the moment.

 

Cheers all

 

Dave

Edited by aardvark
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Hello all.

 

Just to close out this thread. I changed the oil yesterday to Penrite Classic Triumph (from TRR shop). Pressure is now around 20 at idle hot but builds rapidly as revs increase. 50psi occurs earlier than before at around 1700 revs and 70psi is reached at 4000 revs. So much happier now.

 

Thinking about it .... I had a leaky (dribbling) injector around a month ago - misfire and spark plug reeking with petrol - cured with a new injector. Perhaps that thinned the oil?

 

Cheers

 

Dave

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