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Shade Tree Mechanic
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I have a 1928 Chevy Capitol 1 Ton truck. I have about 1200 miles on a fresh engine overhaul. After I have been on the road on a day like today when it was 94 degrees, I come to a stop light, the oil pressure drops from 8 or 10 pounds to zero. On cooler days I don't notice this. Is this because the oil is so thined due to the heat? Should I run a higher viscisity oil when in hot weather? When I first start the truck in the morning the pressure is 12 pounds. The when it warms up it runs around 8-10 pounds. But as stated, when it get up into the 90's outside, I see the pressure drop and go to zero at idle...?? Thanks, Maxie.
"Preserving the old fashion way... for the fun of it."
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Hi
What oil weight do you use?
yes use heavier weight.
Ken 45145
I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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Maxie remember you have a splash lubrication system. Heavy oil will not splash/lubricate the engine properly. The pressure isn't as important as volume of oil getting to the troughs.One or two PSI is OK at hot idle. If it's zero then take the time to diagnoise the problem. I wouldn't cover up the problem with heavy oil. You can do a lot of damage with heavy oil. 10W30 should work just fine.
Last edited by SSG26K; 05/30/09 10:27 PM.
Steve
'25 Superior "K", '79 Corvette , '72 Corvette LT-1 & 1965 Corvette Coupe
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I wouldn't use anything heavier than #30. If it drops to ZERO with #30 there is probably a pump problem.
Gene Schneider
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Maxie remember you have a splash lubrication system. Heavy oil will not splash/lubricate the engine properly. The pressure isn't as important as volume of oil getting to the troughs.One or two PSI is OK at hot idle. If it's zero then take the time to diagnoise the problem. I wouldn't cover up the problem with heavy oil. You can do a lot of damage with heavy oil. 10W30 should work just fine. Right on! DON'T go to a heavh oil It will be worse on the engine.
Life's a long winding trail, love Jesus and ride a good horse!
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Learn someting new every day!
I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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Shade Tree Mechanic
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One or two PSI is OK at hot idle. Curious, if one or two is ok at hot idle, what is okay when it is cold?? I recently had an oil pump failure that has me out of business for a while. When I get it all put back together I certainly don't want to go through all this again! It appears to be pumping good, but still not much pressure.
Thanks,
Bruce
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hi
my 27 chevy 171 pumps between 5-10 lbs sometimes I think it hits 12.
I run 10 w 30 and change very often. It smokes once and a while and leaks some but starts up in an instant providing lots of pleasure for my family.
These low pressure readings 1-2 lbs sounds low.
Ken 45145
Last edited by Ken_Naber; 06/03/09 10:18 PM.
I have a 1927 Chevy Capital AA 4 Door also a 1927 Chevy Touring car, a 1936 Chevy 1/2 ton and a 2010 Corvette LT3 Convertible and a 1953 Packard Caribbean. My tow car is a 2011 Suburban.
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Check to see if the restrictor fitting is attached to the oil filter.It should have a small dia hole in it,as the oil filter is only working on the "bypass" system.You could try disconnecting the oil feed pipe to the filter with a suitable fitting,and if that brings your oil pressure up,you'll have something to investigate. The other scenario is that the oil pressure relief valve is not seating properly.A mates '28 roadster had a similar problem.Pressure was 6-8 lbs.hot & driving,but barely 0-2 lbs at idle.I ended up stripping the relief valve,re machining the tapered valve seat,and making a new tapered valve head & fitting it to a new stem.After re-assembly of the spring and valve assembly,the pressure is now just over 15 lbs.(cold fast idle),and around the 8-12 lb mark driving. 
CJP'S 29
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Grease Monkey
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Grease Monkey
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Hi CJP'S 29,
Please explain how you fixed the oil pressure relief valve. I have two 1928 chevys that have no oil pressure. Thank you.
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When I rebuilt the '28 engine in my truck Lurch, I found some items of concern in the oil distributor. Before the rebuild, Lurch's oil pressure was around 10 psi cold and 3-4 psi hot. Here's a link to the discussion of the oil distributor: Resurrectiong a '28 4 banger - oil distributorI should also say that since I was sinking some serious money and time into the rebuild, I bought a new gear-type oil pump (from Billy Possum - http://www.billypossum.com/Catalog/Catalog.php) and replaced the vane-type pump, mainly for my peace of mind. After the rebuild, the oil pressure goes up to 15+ psi cold and remains around 8 psi hot. BTW, I took out the oil restrictor at the oil filter line since I had a new, higher pressure oil pump. Cheers, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
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CJP'S 29
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Shade Tree Mechanic
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A couple other things to look at if you haven't already:
1) Assuming you are using the original Vane pump, does the spring between the pump vanes need to be replaced?
2) Have you bled the line up to the oil pressure gauge?
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In previous discussions along these lines, various folks have said that it is not a good idea to bleed the line up to the oil pressure gauge because the air pocket is necessary to protect the gauge.
Regards, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
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Shade Tree Mechanic
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Hi Dean,
Interesting on the oil gauge, I guess I'm not sure how oil would hurt the gauge? My thought on bleeding the line is I was removing a majority of the air but an air pocket will inevitably form regardless when the engine is off for any period of time. That said by reducing the volume of compressible gas (air) it would give you better response on the oil pressure gauge.
I had trouble with my oil gauge consistently registering pressure even when it was clear I had flow. After starting, it would usually take a good 30 seconds or more before pressure would register on the gauge. Once, I had driven off and looked down after several blocks and saw it was still registering 0 PSI and my heart sank, cracked and oil line and all the sudden I was reading full oil pressure. After bleeding the majority of the air from the line I have not had that problem. The pressure will spike the gauge when cold (i have a 0-10 PSI gauge from a '24) and will hover between 8-10 when warm and driving, drops down to ~6 or so when idling hot.
-Tyler
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Hi Tyler,
I agree that a small air pocket in the oil line to the gauge is better than a large air pocket. I suspect the air pocket cushions the pressure shock to the gauge, thus providing a little protection from blowing its innards out. This is pure speculation on my part.
Cheers, Dean
Dean 'Rustoholic' Meltz old and ugly is beautiful!
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Good speculation Rustoholic!  
RAY Chevradioman http://www.vccacolumbiariverregion.org/1925 Superior K Roadster 1928 Convertible, Sport, Cabriolet 1933 Eagle, Coupe 1941 Master Deluxe 5-Passenger Coupe 1950 Styleline Deluxe 4-Door Sedan 1950 Styleline Deluxe Convertible 2002 Pontiac, Montana, Passenger Van 2014 Impala, 4-Door Sedan, White Diamond, LTZ 2017 Silverado, Double Cab, Z71, 4X4, White, Standard Bed, LTZ If you need a shoulder to cry on, pull off to the side of the road. Death is the number 1 killer in the world.
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My observation is that there seems to be a "sweet spot" for the amount of air in the line to an oil pressure gauge. I agree that a little helps damp out the pressure surges and variation. Too much and the gauge becomes almost non-responsive because the oil is trying to compress so much air.
My first experience with this was on a '73 Chevy Van with a 350. It had a mechanical gauge that would vibrate and buzz unless you bled the line with the engine running. You did not have to let all the air out, just some. The dealer fixed it long term by routing the line to a different pressure port on the engine. Never had a problem after that.
Rusty
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The viscosity of air is a teensy fraction of oil so the response at the gauge will be much faster with air than oil. Bleeding some air will dampen the gauge needle movement which will be good in most cases.
How Sweet the roar of a Chevy four!
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I noticed my oil gauge wasn't registering when started today so I cracked the line behind the gauge and oil pressure went right up to 8 psi. I never had to do that before. I guess there was too much of an air
cushion.
Last edited by SSG26K; 05/01/20 01:44 PM.
Steve
'25 Superior "K", '79 Corvette , '72 Corvette LT-1 & 1965 Corvette Coupe
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