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Tue Aug 12, 2014 2:00 pm

Hi, I recently installed a VDO oil pressure gauge in my 79 bus with dual-post sending unit. I've learned why my oil lite was coming on but after the next hot highway run I noticed hwy speed readings as low as 20psi and only as high as 30psi. These readings are mostly lower than Bentley's minimum spec of 28psi. At first start when the oil is cool the reading is 55psi. Debating whether to abruptly end my holiday and head back home to the city. I did check my pressure relief valve and all seems well there. I went to check the oil control valve (between cyl#1 pushrod tubes) and found only a deep socket without threads and a smooth round bottom. Does my engine (GE022680) not have this valve? Any tips greatly appreciated..

Thx, Andrew

Tue Aug 12, 2014 2:09 pm

forgot to mention I'm using Castrol 20-50 and outside temps were in the low 80's

Tue Aug 12, 2014 2:15 pm

GE does not have the second one.

We run 20-50 and get about 15 - 18 PSI per 1000 RPM when it is 80F outside. So at freeway speed of 3000 RPM we will see 45 - 55 PSI of pressure. Our engine is a GD with solid lifters. Same basic case as yours.

To minimize your risk - keep the RPM down and be sure it is always up to the full mark. Also - a hot highway run should be at 60 - 65 MPH flat and level. The engine cannot shed heat any faster than that, especially at sea level or below 4,000' ASL. If you are driving 70 -75 MPH your oil may be getting up close to 300F which will make it very thin.

Tue Aug 12, 2014 3:08 pm

head temp gauge showed temps not overly hot, max speed was around 60mph near sea-level. Also shouldn't FI sys adjust mixture to keep temps down?

Tue Aug 12, 2014 4:04 pm

skimhead wrote: head temp gauge showed temps not overly hot, max speed was around 60mph near sea-level. Also shouldn't FI sys adjust mixture to keep temps down?

you probably have issues if you were seeing that low of oil pressure at 60 mph with 20/50 oil. The question is where and why. It could be worn bearings. It could be debris is covering the oil cooler so the oil gets really hot. It could also be a worn pump. When you get home you might pull the engine and tin, and check the oil cooler to be sure it is clean and not covered with oil and a mouse nest. Also - make sure the shroud flaps are opening all the way. If the spring broke the air flaps might be off a little enough that the oil cooler is not getting the right amount of air. If those things are Ok then look at buying a spare pump and having Phil (whip 618) tighten it up for you.

Wed Aug 13, 2014 11:02 am

skimhead wrote: head temp gauge showed temps not overly hot, max speed was around 60mph near sea-level. Also shouldn't FI sys adjust mixture to keep temps down?

FYI: the FI isn't as smart as the EFI we have today, it doesn't adjust anything, it simply has a base amount of fuel it squirts into the cylinders at idle then adds to that base amount based on the amount of air it sees passing the AFM.

it's up to the bus owner to keep the temps down :)

Wed Aug 13, 2014 11:18 am

If your head temperatures are not high then your tune up is fine. Oil temps/pressures and head temps are not closely related. Have you pulled the relief valve and checked that the spring is the correct length? An 1/8" short and you will notice considerably higher oil temps. If short, you can either shim the old spring a bit or buy a new one.

Wed Aug 13, 2014 12:57 pm

Maybe you aren't getting a good ground to the sender? Is it mounted with an extension hose like this?

If you have an ohm meter you can check the resistance between the sender and the engine case. It should be very low.

Wed Aug 13, 2014 5:10 pm

I checked relief plunger for sticking, it fell right out, but I didn't check spring length as there would unlikely be another one avail before home

Fri Aug 29, 2014 10:30 pm

I finally checked the pressure relief valve spring length. It is 2.25 inches long. Bentley says it should be 1.75 inches long. Could this be causing low oil pressure readings? Does anyone know where to buy the correct spring for engine # GE022680? Also very confused by VDO's wiring diagrams. Does WK terminal go to VDO gauge and G terminal to the idiot lite? And should VDO's gauge lites be so dim you can't read them at nite? The bulb's are working. Can an air PSI gauge be used to measure oil pressure?

Fri Aug 29, 2014 10:56 pm

Please don't freak out on the un-loaded length of spring, I'm staring at
the book right now and their technical specs have to do with applying
"load" to arrive at 1 9/16ths length, with tension of 15-19.4 lbs applied.
Your free length will differ wildly. I assume you need an appliance like
a valve spring tester to do justice to VW spec check.

Sat Sep 13, 2014 11:59 am

Can an air PSI gauge be used to measure oil pressure?

Sat Sep 13, 2014 12:24 pm

skimhead wrote: Can an air PSI gauge be used to measure oil pressure?

Yes it can. As far as inner workings go....most gauges operate the same and with the same type of mechanism. Just do not let it stay attached with hot oil. It should be ok but most notln hot climate gauges are good to about 185-200 f.

Also use a hose and fill the hose with oil first. Air locked in the line will give an alternating reading. Ray

Sat Sep 13, 2014 12:29 pm

skimhead wrote: Can an air PSI gauge be used to measure oil pressure?

Sure, if you have the fittings to hook it up, but you want a long enough hose to make sure you don't actually get oil into the air gauge.

Sat Sep 13, 2014 12:30 pm

Greg in GA wrote: skimhead wrote: head temp gauge showed temps not overly hot, max speed was around 60mph near sea-level. Also shouldn't FI sys adjust mixture to keep temps down?

FYI: the FI isn't as smart as the EFI we have today, it doesn't adjust anything, it simply has a base amount of fuel it squirts into the cylinders at idle then adds to that base amount based on the amount of air it sees passing the AFM.

it's up to the bus owner to keep the temps down :)

Not quite true. L-jet does a pretty reasonable job of compensating for altitude changes. As air density drops, the flap does not move as far as it does with the same throttle setting at lower altitudes. It forces your right foot to keep up with the differential as far as load response goes.
The baseline mixture will get a boost as well because the fuel pressure regulator will run generally richer because the engine does not develop as much vacuum at altitude.

On the other hand....D-jet does indeed require and extra additive control that is a plug in. It adds extra fuel baseline as air density drops below a certain point.

But they are not as good at doing these things as modern injection. Ray

Sat Sep 13, 2014 12:32 pm

skimhead wrote: Can an air PSI gauge be used to measure oil pressure?

Pressure is pressure, the medium does not matter (unless it's corrosive or otherwise damaging to the gauge components). Usually, even with measuring
the pressure of fluids, it's actually the air trapped in the lines and gauge that you are directly measuring the pressure of.

Sat Sep 13, 2014 1:04 pm

merlinj79 wrote: skimhead wrote: Can an air PSI gauge be used to measure oil pressure?

Sure, if you have the fittings to hook it up, but you want a long enough hose to make sure you don't actually get oil into the air gauge.

Oil, air and water gauges are identical inside. The oil wont hurt a water gauge...but hot oil gauges usually have a stainless bourdon tube instead of brass or phosphor bronze so the high heat does not mess with it. Ray

Mon Sep 22, 2014 10:10 pm

Hi, I'm wondering what the consequence would be if I were to run my motor (oil warm) without pressure relief valve installed to see if the spring length may be affecting my low oil pressure problem?

Tue Sep 23, 2014 6:42 am

I just went back and re-read this thread. I can report that the bus I'm currently working on does the same as the OP's bus. On start the oil pressure is close to 60. Once warmed up the oil pressure is around 20 psi on the freeway. Here's some facts.

1) Valvoline 20W50 blend. Mahle filter.
2) Newly installed (rebuilt) type 4 oil pump looks good per Bentley
3) Remote mounted dual pole VDO sender (80 psi with matching gauge)
4) Oil pressure relief inspected. Found to be sloppy. Might need to machine oversize and custom make a new plunger. Spring not measured.
5) Working thermostatic flap system with new stat.
6) GD case

Engine does not appear to be hot. I have no mounted oil temp gauge but could try my dip stick mechanic oil temp gauge or use a laser temp gauge. Wondering if the hose extension could be the problem? So, here's some things I could do.

1) Install mechanical gauge and have partner verify readings at speed.
2) Oversize oil pressure relief plunger and bore. Check spring.
3) Measure oil temp (dip stick gauge) as well as case temp once stopped.

New oil pump installed

OP sender installation

Anyone have more ideas?

Tue Oct 14, 2014 1:53 pm

Hi, before I dive into removing my oil pump can anyone assure me that the oil pressure relief spring cannot cause low oil pressure, given that the oil temperature is staying below 200F degrees?

Thx, Andrew