Oil Pressure Again : MGA Forum : MG Experience Forums : The MG Experience

Oil Pressure Again #1
Nik Nikolai Sklyadnev Moscow, Russian Federation	Posted: July 24, 2012 08:47AM Registered: 3 years ago Posts: 25

Hello.
Last Sunday had the first test drive with just rebuilt engine and it seems it has some oil pressure
problems. When I start a cold engine the pressure at idle is about 60 psi. After 10 minutes of idling temperature rises to 190dF and oil pressure is 40 psi at idle (800 rpm) and 60 psi at 2500rpm but after about next 10 minutes of idling or some time of driving oil pressure falls to to 50psi at 2500 rpm and 20 - 30psi at idle and oil pressure gauge needle begin wavering from 20 to 30 psi, temperature is the same 190dF. Pointing higher pressure the needle is stable.
My engine is a standard 1500 engine with correct main and big end bearings clearance ( checked it by myself), 20W50 mineral oil. Unfortunately I didn’t check oil pump clearance.
Thank you if anybody have any ideas about wavering needle and a bit low idling pressure for rebuilt engine.
Regards, Nick

Edited 2 time(s). Last edit at 07/24/2012 12:01PM by Nik.

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Re: Oil Pressure Again #2
bills Bill Spohn W. Vancouver, BC, Canada 1956 MG MGA 1958 MG MGA Twin-Cam 1962 MG MGA MkII Coupe 1965 Jensen CV8 1969 Lamborghini Countach → more	Posted: July 24, 2012 11:48AM Registered: 8 years ago Posts: 9,160

50 psi hot at 2500 isn't that bad. The idle pressure can indicate excessive clearances, but 20-30 isn't that bad - I've seen 10 psi on worn engines. I hesitate to suggest this because many engines have had shimmed relief valves to no good end, but you could put one MGB shim in there if it makes you happier. Otherwise I'd just keep an eye on it and drive it.

Bill Spohn www.rhodo.citymax.com/carstuff.html
1958 MGA Twincam (race car), 1962 MGA Deluxe Coupe
1969 MGC roadster, 1957 Jamaican MGA
1965 Jensen CV8, 1971 Jensen Interceptor
1969 Lamborghini Islero S, 1988 Fiero GT turbo
2009 Pontiac Solstice GXP Coupe
West Vancouver BC

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Re: Oil Pressure Again #3
Bob Agar Robert Agar Green Valley, AZ, USA 1953 MG TD "Myrtle Anne" 1957 MG MGA 1500 Coupe "Miss Scarlett" ~ For Sale ! ~ 1974 MG MGB "The Mistress"	Posted: July 24, 2012 11:57AM Registered: 5 years ago Posts: 1,997

Wavering needle likely due to air in the flex line to the gauge. See Barney's website.

1974.5 MBG Tourer with Weber 32/36 mod and AC.
1957 MGA 1500 Coupe - Stock and original except paint
1953 MG TD - Original car with no mods

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Re: Oil Pressure Again #4
bills Bill Spohn W. Vancouver, BC, Canada 1956 MG MGA 1958 MG MGA Twin-Cam 1962 MG MGA MkII Coupe 1965 Jensen CV8 1969 Lamborghini Countach → more	Posted: July 24, 2012 12:03PM Registered: 8 years ago Posts: 9,160

In reply to # 2128479 by Bob Agar See Barney's website.

I sometimes think that a new button on the reply screen that says exactly that might be a good idea! winking smiley

Bill Spohn www.rhodo.citymax.com/carstuff.html
1958 MGA Twincam (race car), 1962 MGA Deluxe Coupe
1969 MGC roadster, 1957 Jamaican MGA
1965 Jensen CV8, 1971 Jensen Interceptor
1969 Lamborghini Islero S, 1988 Fiero GT turbo
2009 Pontiac Solstice GXP Coupe
West Vancouver BC

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Re: Oil Pressure Again #5
bobs77vet bob k arlington, va, USA	Posted: July 24, 2012 12:44PM Registered: 1 year ago Posts: 637

Nick how good is the oil you are using? and how many miles on the engine now? i like to change my oil after the initial start up and then again in 500 miles. maybe you had some gas getting by the rings as the rings were breaking in and this diluted the oil some. nothing to worry about just normal seating of the rings, did you flood the engine by any chance when you were trying to start it?. change the oil soon and see what happens.

Edited 1 time(s). Last edit at 07/24/2012 12:46PM by bobs77vet.

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Re: Oil Pressure Again #6
wrayg wray brady bethel park,pa, USA 1958 Triumph TR3 1960 MG MGA 1961 Triumph TR4 1964 Triumph TR4	Posted: July 24, 2012 12:51PM Registered: 5 years ago Posts: 91

My car is out of long term slumber and had a stuck piston that came free with some help. Compression is 120 across the board which is very good. I took it to the Pittsburgh Vintage Gran Prix both Saturday and Sunday. Saturday drove thru city traffic and when at 185 egrees oil pressure is 45-50 or so over 2500 rpm's and 10 at idle. Sunday I drove the interstate and did 10 plus miles at around 55 MPH. Oil pressure was 45-50 and then dropped gradually to 38-40. Once I got it in city traffic it was back to 10 at idle and 45 at higher rpms. So why does the prolonged higher speed RPM reduce oil pressure. theory's might be a sticky pressure relief valve but more likely in need of rod and perhaps main bearings. Appreciate any input from the board. I have attached a photo of my son and I running the parade lap for MG mark of year participants. There is no queastion why many drivers treat this course cautiously, most of the "guard rails" are either trees or stone walls. The hay bales won't help much.

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Re: Oil Pressure Again #7
bills Bill Spohn W. Vancouver, BC, Canada 1956 MG MGA 1958 MG MGA Twin-Cam 1962 MG MGA MkII Coupe 1965 Jensen CV8 1969 Lamborghini Countach → more	Posted: July 24, 2012 12:54PM Registered: 8 years ago Posts: 9,160

Easy answer. Oil gets thinner as it heats up. Using higher engine speeds heats oil more.

Are you running an oil cooler?

Bill Spohn www.rhodo.citymax.com/carstuff.html
1958 MGA Twincam (race car), 1962 MGA Deluxe Coupe
1969 MGC roadster, 1957 Jamaican MGA
1965 Jensen CV8, 1971 Jensen Interceptor
1969 Lamborghini Islero S, 1988 Fiero GT turbo
2009 Pontiac Solstice GXP Coupe
West Vancouver BC

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Re: Oil Pressure Again #8
Nik Nikolai Sklyadnev Moscow, Russian Federation	Posted: July 24, 2012 01:26PM Registered: 3 years ago Posts: 25

Bob,
I use TOTAL 20W50 oil, I don’t know whether you use this brand of oil in States and I didn’t
use any additional floods during initial start up After about 2 hours of idling during few days the engine has just 10 miles. Because I didn’t rebuild oil pump It could be a reason of not high pressure for newly rebuilt engine but I can’t explain the wavering of the gage needle.
I know Barney’s article of bleeding oil pressure gage line but as I could understand Barney’s test, air in line make movement of needle more smooth and some pressure change doesn’t lead to fast needle wavering.

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Re: Oil Pressure Again #9
wrayg wray brady bethel park,pa, USA 1958 Triumph TR3 1960 MG MGA 1961 Triumph TR4 1964 Triumph TR4	Posted: July 24, 2012 01:51PM Registered: 5 years ago Posts: 91

No oil cooler Bill, but the engine temparature is marginally less on the highway than in town.

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Re: Oil Pressure Again #10
bills Bill Spohn W. Vancouver, BC, Canada 1956 MG MGA 1958 MG MGA Twin-Cam 1962 MG MGA MkII Coupe 1965 Jensen CV8 1969 Lamborghini Countach → more	Posted: July 24, 2012 01:53PM Registered: 8 years ago Posts: 9,160

That's pretty much irrelevant to oil temp.

Bill Spohn www.rhodo.citymax.com/carstuff.html
1958 MGA Twincam (race car), 1962 MGA Deluxe Coupe
1969 MGC roadster, 1957 Jamaican MGA
1965 Jensen CV8, 1971 Jensen Interceptor
1969 Lamborghini Islero S, 1988 Fiero GT turbo
2009 Pontiac Solstice GXP Coupe
West Vancouver BC

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Re: Oil Pressure Again #11
barneymg Barney Gaylord Naperville, Illinois, USA 1958 MG MGA "MGA With An Attitude"	Posted: July 24, 2012 08:30PM Registered: 8 years ago Posts: 2,155

The wavering oil pressure needle is a true reading of actual oil pressure. It is a result of a dithering pressure relief valve under select circumstances. Change engine speed a little and the wavering goes away. This is not harmful, just irritating to look at. Sometimes the wavering oil pressure can be cured by lapping the pressure relief poppet to the engine block.

Oil pressure of 50 to 60 psi at road speed is fine. 40 psi at hot idle is common. 40 psi at road speed and 20 psi at hot idle will concern me enough to fix it. Check condition of the oil pump internal rotors first. If the oil pump looks good, then plan on replacing the connecting rod bearings (and maybe also the main bearings while you're in there).

Oil pressure drops some as oil gets hot and thins out. Expect oil pressure to be a little lower after a hot day putzing around at low speed. Same conditions that make high coolant temperature also make hot oil and lower oil pressure. Oil cooler can increase oi pressure maybe 5 psi at road speed, but doesn't help much in stop and stop traffic.

Modern oil is pretty good with high temperatures, as long as you don't mind the drop in pressure reading with hot oil. I installed the oil cooler when I started trailer towing for serious, but wasn't too concerned about oil temperature otherwise.

Shimming the PR valve to make higher pressure at road speed is a feel good move only, not doing much practical good. The PR valve will open at 50 or higher. Below 50 psi the PR valve is closed and all oil from the pump goes through the engine. When pressure is 40 psi or less, all the shims in the world won't make any difference in oil pressure. When you have 20 psi at idle, a shim is not going to fix anything.

Barney Gaylord
1958 MGA with an attitude - http://MGAguru.com
Notice: - Do not leave a PM for me on the forum server. Send any private message to my personal e-mail address barneymg@mgaguru.com

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Re: Oil Pressure Again #12
mgageoff Geoff Howard Ashburn, VA, USA 1958 MG MGA 1500	Posted: July 24, 2012 09:07PM Registered: 1 year ago Posts: 661

Big bummer. I just noticed I'm now actually below 20 psi (probably about 18) at hot idle. Don't mean to hijack, but I guess I need to get the sump off to check pump, but likely replace bearings... Good thing I just bought a snow car...

Geoff Howard
http://mgaexperiment.blogspot.com
Now Playing on the Blog (1/6/2013): Sagging With Age

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Re: Oil Pressure Again #13
cw6er Chris Wright Columbus, IN (Indy 500 area), USA	Posted: July 25, 2012 01:51AM Registered: 10 months ago Posts: 92

What am I missing? The Workshop Manual calls for oil pressure to be between 30 to 80 psi at normal running with approx. 10 psi at idle. These figures are pretty common, it's the same as my '81 straight 6 pickup.

And isn't 20w50 a bit thick for a new rebuild? Again the Workshop Manual calls for 30 weight oil down to 32º with 20 weight down to 10º and 10 weight below 10º. Sounds like 10w30 to me? I'll probably use 10w40 but not more then 15w40 at most.

You might even get an increase in the oil pressure by switching. I was using 20w50 in my '81 truck and was only reading 35 psi (10 psi Idle) when I switched to 10w40 and the oil pressure went to 48 psi (15 psi Idle) and is still there.

'59 1500 - First car I ever bought in '68 and I still have it.
'60 1600
'67 MG 1100 Sports Sedan
'87 BMW 635

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Re: Oil Pressure Again #14
57Coupe Andy Bloom Grand River, Ohio, USA 1957 MG MGA 1500 Coupe "1957 Coupe"	Posted: July 25, 2012 07:47AM Registered: 1 year ago Posts: 146

I alway break my engines in on SAE40 (Straight) with break in additive. Run it for 250 miles them change out. I would run a straight 40 or 10-40 unless you are in a hot climate. 20-50 in hot climate would be preferred with a cooler. Just my $.02

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Re: Oil Pressure Again #15
bobs77vet bob k arlington, va, USA	Posted: July 25, 2012 02:23PM Registered: 1 year ago Posts: 637

for you guys who like the heavier weight oil you may want to look at the Mobil 1 synthetic 15w-50 oil its formulated for pushrods and non-roller tappets.

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Re: Oil Pressure Again #16
59mgaguy John Terschak Kill Devil Hills, NC, USA 1930 Ford Model A "Jenny" 1959 MG 14/28 "Jessie" 1974 MG MGB "Oooops"	Posted: July 26, 2012 07:07AM Registered: 2 years ago Posts: 882

On my engines on first start up. I run them above idle at a faster RPM for around 45 minutes. Drain then refill and change again after running on the road for 500 miles. And I don't run the engine hard. You would be surprised by the amount of metal in the oil after changing.

John

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Re: Oil Pressure Again #17
cw6er Chris Wright Columbus, IN (Indy 500 area), USA	Posted: July 26, 2012 09:04AM Registered: 10 months ago Posts: 92

In reply to # 2129572 by bobs77vet for you guys who like the heavier weight oil you may want to look at the Mobil 1 synthetic 15w-50 oil its formulated for pushrods and non-roller tappets.

Did you find this information from Mobil somewhere?

Or was it just the fact that it contained the higher levels of zinc for longer then most oils? I don't believe it carries the higher levels of zinc any more?

'59 1500 - First car I ever bought in '68 and I still have it.
'60 1600
'67 MG 1100 Sports Sedan
'87 BMW 635

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Re: Oil Pressure Again #18
cschaefer Chuck Schaefer West Chicago,IL, USA	Posted: July 26, 2012 09:33AM Registered: 4 years ago Posts: 658

from http://www.mobiloil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf
Last update date:10/17/2011

Mobil 1
15W-50
Phosphorus = 1200
Zinc = 1300
Recommended Consumer Applications = HT/HS applications. Racing and Flat tappet applications.

Edited 1 time(s). Last edit at 07/26/2012 09:34AM by cschaefer.

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Re: Oil Pressure Again #19
Tbird Eric Taylor CLT, NC, USA 1960 MG MGA 1600 1960 MG MGA 1600	Posted: July 26, 2012 10:16AM Registered: 1 year ago Posts: 456

Maybe a worn pressure release valve sticking or a weak spring. Pretty cheap to replace both.

We've been discussing the zinc content of oils on the Tbird forum. There are motorcycle oils (Spectro Motor Guard) that contain higher levels of zinc and Quaker State has developed one specifically with higher zinc levels. You can get the Quaker State cheap at Wal-Fart. (well maybe not in Moscow) DEFY
http://www.walmart.com/ip/Quaker-State-Higher-Mileage-Engine-10W30-Motor-Oil-5-Quart/14958695

Eric

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Re: Oil Pressure Again #20
cw6er Chris Wright Columbus, IN (Indy 500 area), USA	Posted: July 26, 2012 10:41AM Registered: 10 months ago Posts: 92

In reply to # 2130133 by cschaefer from http://www.mobiloil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf
Last update date:10/17/2011

Mobil 1
15W-50
Phosphorus = 1200
Zinc = 1300
Recommended Consumer Applications = HT/HS applications. Racing and Flat tappet applications.

Thanks! The last time I looked, the zinc levels had been lowered, It looks like they put the zinc back in. Good for them! This is definitely going into my '87 635 Bimmer (the book calls for this very weight). Hopefully the the full synthetic won't start too much external lubrication!?!

How abut the "A"? Anybody using it in their MGA?

'59 1500 - First car I ever bought in '68 and I still have it.
'60 1600
'67 MG 1100 Sports Sedan
'87 BMW 635

Edited 1 time(s). Last edit at 07/26/2012 11:01AM by cw6er.

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