Oil pressure questions....

[Doc in AZ]

ok, so this is a novel of a post, i'm hoping you guys will read it through and let me know what you think.

i've been working on my old econoline with a 200 I6 from a 65 falcon, we think. internal specs are unknown aside from how nice and fresh everything looked when we pulled the valve cover. no build up inside the head, always cranked right up and shut down immediately when i turned off the key. unlike a lot of the older motors i deal with that just kind of spool down when you turn off the key due to low compression.

we are finally out of the 110*+ weather here in Phoenix, AZ. and i have fought all summer to keep this thing from getting too hot. but a couple weeks ago something went wrong.

here's where i'm at with things...

rebuilt radiator - 3 core brass
new water pump
192* thermostat
15w40 rotella oil
DSII distributor
MSD 6AL
stock plugs @ stock gap
stock 1BBL carb

it seems to run about 100-110* over ambient air temps. so on days it was 115* going 55mph on the interstate my temp gauge (aftermarket with numbered graduation not just hot and cold range) would start getting above 220* and i would have to get off the freeway. gearing is set up to run 55mph @ 2500 RPM and 70mph @ 3000 rpm.

a couple weeks ago on my way home in the evening (over night lows of 95* yuck!) and temp gauge was steady about 205* then the bus started feeling a little sluggish & the temp gauge started rising, lost more power, started pinging on acceleration and the engine started rattling pretty loudly.

clutch in - check. put it in neutral - check. turn off key - check. call the tower and have them clear the runway for emergency auto-rotation landing with emergency crews standing by... lol... actually, just coast to the next exit and see what happened.

i thought maybe i blew a hose or something and it got hot faster than the gauge could report it. there was nothing visibly wrong with the engine. oil was maybe a pint low, radiator had water, nothing leaking, steaming or smoking. hmmmmm. after about 10 minutes i decided to hit the key and see if it would even turn over. much to my surprise it started right up. it sounded a lot like my old 12V cummins but wasn't smoking or anything. i was about 2 miles from the house and figured i would drive it and see what happened... if it blew i'd rebuild it, if it didn't i'd keep driving it.

i got on the frontage road and made my way up to about 40mph and let it coast with the engine running to keep air moving over the engine and radiator and it was running at 200* and quieting down. by the time i got home it sounded like it normally would after a 20 mile drive on the freeway.

i expected it to be locked up when i went to start it the next morning but it cranked right up and sounded fine. i was driving it to my shop to work on it but only made it about 5 miles when it started getting loud again so i pulled off and called a wrecker... those guys at USAA road-side assistance know me by name now... lol. once i got it back home i ran through the valves and found a bent push rod on #4 cylinder. it was bent enough to rub the engine block but was still traveling up and down and working the rocker. it looked like it had been that way for a while and the valve was correctly adjusted to the bent push rod. i checked the valve operation and it seems to move freely not like it was bent and wedging it's self in the guide. i straightened the push rod and put it all back together.

once i got it running again it was puffing a little smoke from the breather but not bad, and if i revved it real quick it would puff a little blue smoke out the tail pipe... meh, looks like the rings collapsed a little. but above 2000 rpm it starts dripping oil out of the breather on top of the valve cover... yup, looks like blow-by.

ok, so enough history, here's the problem.

i connected the aftermarket oil pressure gauge yesterday to see what was going on, i ran the motor to bleed the supply line before i tightened it down at the gauge.

oil pressure at idle (650rpm) with engine at 180* is about 35psi, it only goes up to about 45psi at 3000 rpm and that seems ok to me. but any time i run on the freeway (55mph @ 2500rpm) it doesn't take long before you see the oil pressure gauge start to drop off and hear the rods & valves start to complain. it drops slowly at first down to about 30psi then it starts to drop a little quicker and will go as low as 10psi before i push in the clutch. i have never had the factory oil light come on when this happens and it has a brand new sending unit for the idiot light.

the first time i saw this i got real nervous and put in the clutch and watched the gauge while i had my finger on speed dial for the tow truck. at an idle, coasting down the freeway, it stayed about 10psi for a second or two, wiggled a little then jumped right back up to 45psi and the engine sounded happy again.

i drove another mile, saw the same thing, i did the same thing, the engine did the same thing. hmmmmmm. so in the interest of trouble shooting i just stayed on the freeway and tried different things.

this is the final analysis... at a steady speed on flat and level ground cruising down the freeway, when the oil pressure starts to go down, i leave it in gear and just let off the gas and before i can count to three (one potato - two potato - three.... oh, there's the oil pressure) it's back where it should be. it also has a slight miss under acceleration, no so much one that you feel, but you can hear it if you are driving next to a wall, but otherwise it's a smooth idle and quiet cruise. so now the engine water temp is much more stable (at thermostat temp of 192*) where as before it would stay about 200-205* even in 110*+ heat then after about 5 minutes on the freeway it would start rising real quick til i got to 220 and i would have to get off the fwy.

i have a few ideas what it might be but am interested in hearing other suggestions based on first hand experience / knowledge.

- broken/loose/damaged oil pump pick up tube
- old and worn oil pump that is cavitating or losing pressure at higher rpm
- worn rod or main bearing that is allowing oil to "flow" rather than maintain "pressure" with a tight factory tolerance
- oil is not making it back down to the oil pan quickly enough to maintain pressure but letting off the gas for a three-count is long enough for it to drain back down

thanks for looking

-doc

 

[FalconSedanDelivery]

sounds like blocked returns keeping the oil from draining back , try an extra quart , one wont hurt , and may be a quick fix , you are running 5 now right ? it is possible you ran it low enough that a lifter stuck and that was the bent pushrod problem .

 

[Mustang_Geezer]

When it happened did you get a huge cloud of smoke out of the exhaust?

Back in 2006 my engine started doing that....

Pulled the motor apart and found the piston rings in several dozen pieces. It ended up it was sucking so much oil past the rings into the combustion chamber that it sounded like it was killing the motor. Oil pressure would drop, temp would sky rocket, engine would start hammering and you would get this huge cloud of smoke behind the car.

It would only do it at 55-60 mph. At idle or below 55 mph it would run fine.Stop and pull over for a few minutes and it would be fine again. It only ran like that for a couple of weeks before it started dropping cylinders because of dripping wet oil fouled plugs.

Do a compression test and better yet a cylinder leak down test. Hows the plugs look?

Have fun.

Doug

 

[Doc in AZ]

i pulled the plugs yesterday before i swapped carbs. they were about 2 weeks old and had some oil burnt to them but not fouled out. unfortunately they were covered in soot from the carb taking a dive on me so i don't know how all the colors were to indicate anything.

as for the big puff of magic smoke... well i have no idea. it was dusk and people were just beginning to turn their headlights on and i couldn't really see much behind me with the headlights in my mirrors. but i've blown enough motors that when it got hot and started puffing out the breather and tail pipe at idle i knew i killed some rings.

 

[CobraSix]

Not that I've seen this on car engines, but seen similar on old marine diesels I used to work on.

How's your PCV valve? I think it's a odd ball, but could fit the symptoms. If you have a bent rod, as the engine warms up, the adjustment could go out a little(slight miss). That could allow for the cylinder to vent into the crankcase. That would have the effect of increasing the pressure your pump has to pump against (though maybe it would equalize since it would increase pressure in the entire crank and head region). Then when you let off the gas, it's allowing some of the pressure to vent out since the engine is not under load.

Just is some way, it sounds like our engines when they were about to experience a crankcase explosion (super bad on a 5000HP diesel). oil pressure would drop, engine crank pressure increase. If we throttled back for a minute, it usually went away and we'd be fine.

Also, have you checked your oil lately? Any fuel contamination?

 

[Doc in AZ]

that is a very interesting theory.

i've never run into that before. the dynamics make sense - pressure fighting pressure - but i'm not sure how it plays into what's happening. it makes sense that with a wet sump system if there were too much internal pressure it might prevent the oil from leaving the galleys. i was just talking through this with a buddy of mine over the weekend & as we played with it in the parking lot we could get it to drop pressure and then i would let off the gas and idle it back down slowly, but on the freeway it's only a momentary pause with the clutch still engaged and dropping about 100rpm that will allow it settle in at a "normal" reading. one thing that popped into my head the other day was that when i was swapping in the DSII i was having trouble getting it to drop in. i thought it was just the sealing o-ring on the housing that slips into the block. you can't see much besides the top of the motor working on this thing inside the dog house so i just put more grease on the o-ring and was tapping on the center shaft of the dizzy with a small plastic head hammer. it didn't move at all so i pulled it back out and realized i had the shaft misaligned with the oil pump hex drive thing. with that being said, is there something inside the oil pump that could have been damaged by tapping in on that hex drive via the dizzy?

oil is good, i just changed it when i dropped the pan and cleaned the pump screen. i filled it up with 20-50 and added a pint of Teflon lubricant as well. i have also pretty much religiously added marvel to it about once a month for the last year that i've owned it to keep it in good shape.

the pcv that was on this motor pointed straight up and went to the manifold. because of the dog house on top closing so tight to the valve cover and knocking the hose loose all the time i ended up installing a pcv valve that had a 90* fitting on it. i had to bump the idle up a bit to keep it from chattering and causing a bit of an intake leak. once i got it up to about 750rpm it quit rattling and smoothed out but still seemed a bit problematic so i ended up routing the pcv hose to the air filter housing. maybe i'll move it back to the manifold and see what happens. although i didn't have an oil pressure gauge when it was connected to the manifold it would start to make noise like it was starving for oil at a steady rpm before and i would have to let off the throttle for a second to get it to get oil flow.

it has no baffle in the valve cover below the oil fill so along with the puff of smoke that comes out of the breather after it warms up anything above about 2000 rpm causes it to start blowing oil out of the breather and it pools up in the intake manifold. but i'm religious about checking the oil and have never run it more than a pint low.

 

[CobraSix]

If you are adding oil (or marvel) that often, I think you have rings that are toast, or a bearing that is wiped. I've only used the Teflon stuff on one car and it was a mistake never to be repeated. Caused all sorts of havoc on the oil system. Such that I never had oil pressure at idle once the engine warmed up. Engine ran for another 150k miles over 10 years after that without any problems, never burned oil, and never any lifter tick, but definitely no pressure. Make it to 325k miles at which point I donated the car to charity (some nice guy I am, right?).

At least according to the gauges I never had pressue. I even ran a mechanical to make sure it wasn't a sensor issue. Which makes me wonder if that's the culprit. Make sure we aren't combining symptoms. Have you run a mechanic gauge? Maybe the port around the sensor is clogged? If so, could be that while underload, it causes the oil pressure to build up before the sensor, but drop at the sensor (which could cause the oil spitting through the breather due to high back pressure). Then when you let off the gas, the pump is pushing less oil and the pressure across the restriction equalizes some.

Just another hairbrain theory.

 

[nachoman]

My engine has about 45 psi cold, 35 psi at cruising rpms after 10 or miles on the freway in hot (100 degree) weather, and about 10-15 psi at idle when the engine is hottest. This is according to an el-cheapo mechanical gauge. The oil pressure light used to flicker at idle after a long drive on the freeway on a hot day. So, I pulled the pan, and replaced the main and rod bearings and the pump and screen. That was good for another 5 psi at idle. This is a warehouse remanufactured engine, now with about 140k miles. The oil pressue is still low based upon conventional standards, but the car runs great so I don't worry about it.

I'd do two things:

1) Pull the valve cover off and make sure no oil return passages are blocked. Those rubber valve stem seals sometimes get hard and break, and I have found debris partially blocking an oil return passage.
2) Pull the pan, check the main bearings, and replace the pump and screen. They don't cost that much.