low oil pressure is common at idle

[BOBBYR]

HI guys,
I hope you are all doing well. I was wondering, why is it so common to have low oil pressure at idle with these motors? My father owned two austin healeys and one MG and all of them,had the same problem. I would like to know, what would be perfect oil pressure at idle and what do we want when running at high speeds? Also, What is the most common problem causing this? As always, I appreciate your input.
Bobby R

 

[abarth69]

Bobby

How low?

What type of oil should be a good 20w50 like VR1.

I would shim up the oil releif value and see what happens

Cheers

Mark

 

[HEALEYJAG]

Warm idle 40lbs would be nice..

Pete

 

[Keoke]

HI guys,
I hope you are all doing well.

Boby was wondering, why is it so common to have low oil pressure at idle with these motors?

Old Age,Excessive wear, Inadequate cooling, Worn Oil Pressure relief valve/Spring. Loose Plug in an oil gallery, Oil Viscosity too low.

As Mark pointed out the Oil Relief Valve can be shimmed to temporarily raise the oil pressure.


My father owned two austin healeys and one MG and all of them,had the same problem. I would like to know, what would be perfect oil pressure at idle; As Pete said 40 Psi would be nice.


what do we want when running at high speeds?--55-to-60 Psi is a good number.

Also, What is the most common problem causing this? Excessive wear, usually shows up in the Rocker shaft assembly my opinion.---Keoke

 

[LEERIVAS]

Keoke;

As Mark pointed out the Oil Relief Valve can be shimmed to temporarily raise the oil pressure.

Are we talking about the "bullet-shaped" thingamajeegee or the actual spring of the relief valve?

What would decrease and what would increase the oil pressure?

A "shim" to me is a wedge.

--so many questions, so little time--

 

[Keoke]

Keoke;

As Mark pointed out the Oil Relief Valve can be shimmed to temporarily raise the oil pressure.

Are we talking about the "bullet-shaped" thingamajeegee or the actual spring of the relief valve?
\
Both; The "Bullet- Shaped valve can be worn, Or it could be the wrong one, its seat in the block buggered and/ur the spring could have lost some of its pressure.

Shimming effectively shortens the spring increasing its pressure on the valve and its seat,

What would decrease it;
Oilpessure is reduced when spring pressure is lower than specification. Dirt or burs in the block's seat will also lower it,

what would increase the oil pressure?
Increasing the spring 's pressure on the valve. Ie Shimmig

A "shim" to me is a wedge. Nww in this case its just washer
placed inside the Bulet shaped valve
--so many questions, so little time--

Yeah--- --Keoke

 

[BOBBYR]

Hi Keoke,
I'm really glad to hear from you again.I was wondering if you personally had a problem with a rocker assembly.I know that worn rod and main bearing can cause this condition, but I don't think that is the problem with my 65.I too, am betting on a worn rocker assembly.This week, I am changing out all the fluids in the motor ,trans and differential and I did get a new pressure relief spring to install.When I get that done, I'll get the oil heated up and check out that rocker shaft for excessive play and wear.
I would like to thank all the guys, for their help on this problem and if anyone come up with any other ideas, I would appreciate the help.

Bobby R

 

[healeynut]

Keoke;

A "shim" to me is a wedge.

For cars, shims are usually round washers of varying sizes. He's saying to put an appropriately sized washer between the pig and spring.

 

[Keoke]

Hi Keoke,
I'm really glad to hear from you again.I was wondering if you personally had a problem with a rocker assembly

.Yes, on My Miss Blue. Little geysers of oil coming off the assembly instead of a very light flow.--Keoke

I know that worn rod and main bearing can cause this condition, but I don't think that is the problem with my 65.I too, am betting on a worn rocker assembly.This week, I am changing out all the fluids in the motor ,trans and differential and I did get a new pressure relief spring to install.When I get that done, I'll get the oil heated up and check out that rocker shaft for excessive play and wear.
I would like to thank all the guys, for their help on this problem and if anyone come up with any other ideas, I would appreciate the help.

Bobby R

 

[stever]

I still had fairly low oil pressure at idle after rebushing the rocker arms. However, when I went to using the Penrite oil which is designed for our vintage cars my oil pressure at idle problem was MARKEDLY reduced. I forget the gent's name who it was that I used to buy the Penrite oil through but he was a Healey List member in Texas, but anyway, he assured me that the oil pressure would increase at idle if I used the Penrite oil and he was correct. so, my recommendation would be for you to change your oil out to one of the vintage type oils. I use Penrite and I get it via the mail from California. My Texas friend no longer distributes the Penrite oil so I did a 'google' on Penrite and found the USA distributor and ordered it - arrived in a few days. Now, just to be clear the oil pressure still reduces from where it runs at higher RPMs, but does not reduce to a very low pressure level now at idle.

 

[red57]

Another thing to check is the gage itself, it's not impossible for the gage to be off in it's calibration.

I would look at the rockers when running and fully warmed up, you should just see a 'dribble' coming out of the rockers. If this looks good, I would hook up known good gage temporarily to confirm you really have low pressure before staring to tear it down.

An old racers adage is a minimum of 10psi for every 1000rpms.

BTW, ALL motors will have low oil pressure at idle. It's just that a lot of cars have warning lights instead of gages and you don't know how low the pressure is at idle (unless the light comes on).

Dave Phillips

 

[BOBBYR]

Hi Dave,
I know what you mean about the warning lights and I agree with the 10 psi for each 1000 rpms.With the motor that's in this car, the crank and rod bearings look great and it runs really strong.I'm just trying to avoid problems before they happen.I do have a snap on pressure gauge so I'll hook that up and see what that reads.Keoke said that his rocker assm. gave him this problem and I've heard this before from other posts.Thanks for your help.
Bobby R

 

[tahoe healey]

So with the formula of 10 psi / 1000 rpm idle could be 7 or 8 psi? I get 35 to 40 idle and 60 at running speeds.

 

[Keoke]

So with the formula of 10 psi / 1000 rpm idle could be 7 or 8 psi?------ -----Yep---

I get 35 to 40 idle and 60 at running speeds.------OH!!-You spot on & LuckEEEEEEEEEE --- :laugh:

--------------------------Keoke------------------------ :cowboy:

 

[TimK]

My 100,000 mile motor shows 60 lbs. on startup, but after driving 5-10 min. it drops very rapidly to 40 lbs. at 3,500 rpm. Then it shows about 20 lbs. at idle. I've had the rocker shaft rebushed. I have purchased a new relief valve spring, but not yet installed it.

 

[Keoke]

My 100,000 mile motor shows 60 lbs. on startup, but after driving 5-10 min. it drops very rapidly to 40 lbs. at 3,500 rpm. Then it shows about 20 lbs. at idle. I've had the rocker shaft rebushed.


Hi TimK, That sounds about right for a well cared for high mileage Healey engine.--- :thumbsup:----------Keoke

I have purchased a new relief valve spring, but not yet installed it.

 

[twas_brillig]

Our engine (about 65000 miles from new; stored the last 20 or 30 years)had idle pressure when fully warmed up of a bit less than 20 psi. I pulled the oil filler cap and peered in and the rocker flow looked okay; pulled the valve cover and the rockers were fine (just the proverbial dribble).

I pulled the oil pressure over-pressure spring and cone and replaced them both with new (the new spring was about 1/4" longer than the existing one, if memory serves)and idle pressure now is 45 psi when hot. Joy and Happiness!

I'd started a thread in December on oil pressure, asking for wisdom, and did a final update to it with our original and replacement spring lengths - I just did a quick search but was too lazy to actually dig it out. You might want to have a check to compare your original and replacement spring lengths to my experience.

And for those who are wondering why shimming (or increasing) the over pressure spring would help at idle: the cone makes a metal to metal seat. If the seal isn't real good, then oil will bypass this seal, dropping your pressure at idle. Increase the sealing pressure/increase the integrity of the seal/decrease the amount of oil bleeding back into the sump past the leaky seal/oil pressure goes up.

I'm thinking that changing the spring should be a standard rebuild feature, and am wondering if lapping the cone into the block should also be done? Anyone have thoughts?

Doug

 

[TimK]

Thanks Keoke and Doug for the info. Doug, I remember your December thread and tracked it down. It'll come in handy in a month or two when warmer weather comes to the Detroit area and I can work on the Healey again.