The Stovebolt Site Forums The Shop Area Engine Shop "Full pressure 235" vs. "High pressure 235"

So uh.... Time to further expose my ignorance.

So, my beloved bus has low oil pressure. It's got a 235 in it, and no dippers, and an 848 head. I don't know the year of my Canuck block, as I'm too lazy to take the starter off, so I can clearly read the digits. But I guess I should do so.

Do all 235s have high pressure oiling?

Is there such a thing as a full pressure but not high pressure 235?

Am I crazy? I figure I don't really need to worry unless it drops to zero and I hear that terrible deep death rattle that means there is no oil pressure.

When I come off the highway my pressure is low. Really low. About a needle width off of zero low. I don't hear knocking or anything, but I'm curious if it's my oil pump that's knackered or if that's normal-ish. My main bearings do have quite a bit of clearance, 4 thou. But I'd have thought the 40 weight oil would fill up the gaps a little more. Frankly I have no desire to spend $170 on an oil pump for the bus. I can seemingly drive around all day at 35-45 mph without this happening, but when I hit 50 mph for five or ten minutes (the pressure stays at about 20psi) and then come down to idle, the pressure drops like a stone.

What is the year of your 235?

There were lower pressure 235s (1941 through some 235s in 1953) and higher pressure 235s (some in 1953 and all from 54 onwards). All of them were full-pressure relative to their design.

In 1953, the 235s with hydraulic lifers (used on Powerglide equipped cars and Corvettes) were the higher pressure 235s. 1953 manual transmission cars with a 235 (I think that was an option in cars) and all 1953 trucks with a 235 were the lower pressure implementation.

GM referred to both higher and lower pressure 235s as full-pressure engines.

If your truck has an "848" head (3836848) it is a higher pressure 235.

This is not necessarily true, a 1953 splash 235 could have had a 848 head installed on it at some time.

Hy Mr. Lang, the term "high pressure" has been used as a substitute for "full pressure", so essentially both terms mean the same thing. I think there are some 235s with babbited rod bearings. "Full pressure" lubed engines have precision insert bearings in their rods, and their crankshafts are fully rifle drilled to supply oil under pressure to all the bearings in the engine, hope that helps.

I see. I have insert bearings on my conrods. I guess I'll stick an accurate gauge on the oil gallery, and see what the pressure is. Maybe my gauge reads low? Hahaha.

I guess I should stay off the highway until I can put a new oil pump in. Dagnammit.


Also, my oil pan has the bulged sides, so that should make the block not earlier than '56, according to this sweet article that Kurt sent me.

http://pugetsoundvintagechevrolet.org/Programs/6%20cylinder%20engines%20with%20photos.pdf

but to the important question, it does sound like the pressure is lower than desirable, it should be able to keep 5-10# idling when well warmed up, and maybe 30# or more at higher rpm - the speed you've been traveling shouldn't really make that much of a difference .... might start looking for a replacement engine for when you do hear that death rattle

Bill

I have an ad on used victoria for an engine donation! Hahahaha. I am looking for a Buick 320, or a flathead 8 out of a poncho, because I'm an idiot! So far, everyone seems to want money....

On a more practical note, I have an old 216 behind my garage, that will most likely find its way into the 'ol bus. It was "running but smokey" when I got it.

Well now, I cobbled an accurate gauge onto the old bus today. Looks like I have about 5psi at idle, but about 3 psi when just off the highway, and 20 psi when zooming along. Dang.

I suppose there is nothing to do but replace the pump, or get a rebuild kit from the USA.

Christopher,

Have you IDed the year and the application/model of your 235 engine?

No. I'll have a close look at the numbers this morning. Fred sent me a listing of Canadian block numbers.

The term "full pressure" lubrication is not only meaningless but it can also be confusing as to which 235 engine is being discussed: the lower pressure 235s (1941-1953) and the higher pressure 235s (1953-1963) all had full-pressure relative to the design of their different types of lubrication systems - at least as described in various Shop Manuals.

If a 235 owner reads an older Shop Manual (pre-1954), that person will see GM referring to the lower pressure 216/235 engines as having "Full pressure lubrication to the main and camshaft bearings . . .". The older Shop Manuals refer to "full pressure" lubrication all the way back to the first stovebolt engine (1937) - prior to that time, the lubrication was that of a true "splash oil" pre-stovebolt engine ("splash oil" is another often misused term, but that is another topic).

So, if a new member has read only a pre-54 Shop Manual to try to figure out what engine he/she has, and the new member posts the engine ID and someone replies, "good news, you have a full pressure 235, that member might think that his/her engine is the engine described in the pre-1954 Shop Manual.

Christopher,

To answer your question about oil pressure:
You either have a lower-pressure 235 or a higher pressure 235.

The lower pressure 235 has an oil gauge with a range of about 0-30 and the higher pressure 235 has an oil gauge of approximately 0-60.

15 psi or 30 psi in either system while driving is a good pressure. At idle, it is common for an older engine to have lower psi (in both lower-pressure and higher-pressure 235s). As the engine gets older (bearing clearances get wider, etc), the pressure at idle gets lower.

I had a higher pressure 235 that had good pressure when running, but it had very low pressure when idling (around 5 psi). I took out the engine and replaced it when it idled with a 0 psi reading. No sense gambling on when the engine would seize or otherwise break down.

Are you running a bypass oil filter? Is it the original type with oil restrictor?

Yeah, I have a bypass filter on, a Frantz, which restricts even more than the factory unit. It's such a small trickle of oil, I don't know that removing it would make much difference.

I still haven't checked my number, as I'm sawing up bird houses for the local Brownie Troop. today.

Christopher has a full pressure 235. He had the lower end apart recently and I believe it does not have dippers.

Hy Mr. Lang, after having read this entire post, I think you probably have worn bearings where you have not already replaced them, cam bearings included in that. The oil pump provides oil into the oiling system, but it can only maintain pressure in the system if the clearances are not excessive and let the oil "bleed" out of the bearings too quickly. I doubt a new or rebuilt oil pump will cure your problem. If your engine is spewing oil out at high speed, that would indicate high crankcase pressure, that comes from excessive leakage past the piston rings. You said you have done a ring job recently, did you hone the block so the rings could "seat" to the cylinder walls? If you did not hone the block, or if you used "chrome" rings they will take a long time to "seat" if they "seat" at all, hope that helps.

I did hone the block, and the rings I used were NOS Chromflex ones.

Everything seems to be fine and dandy, as long as I don't drive over 40 mph. So, for now, that's what I do, as I need to get to and from work. I think I'll measure up the old 216 sooner, rather than later!