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Strange Oil Pressure

B

Bill Blue

Platinum Level Sponsor
The dash gauge (electric) was showing about 5 psi at idle, so I hooked up a mechanical gauge. It showed a very steady 30 psi at idle. I installed a new VDO sender. The pressure now is 40ish at idle, but drops to low 20's as rpm increases. Totally reverse of what I've ever seen.

Any ideas what is happening? This is with the 2010 Duratec engine. The old sender (VDO) had two terminals and the sender ground was wired directly to the gauge. When the new (single terminal) sender was installed, the ground wire was grounded to the block. Could that cause readings to be reversed? VDO gauge.

I must say that I am not all that impressed with VDO. So far the volt meter and water temp gauges have packed it up. Now this from the oil pressure. Also, at times, the odometer looks like it is sending messages in Chinese.

Bill
 
Barry

Barry

Diamond Level Sponsor
Bill Blue said:
The dash gauge (electric) was showing about 5 psi at idle, so I hooked up a mechanical gauge. It showed a very steady 30 psi at idle. I installed a new VDO sender. The pressure now is 40ish at idle, but drops to low 20's as rpm increases. Totally reverse of what I've ever seen.

Any ideas what is happening? This is with the 2010 Duratec engine. The old sender (VDO) had two terminals and the sender ground was wired directly to the gauge. When the new (single terminal) sender was installed, the ground wire was grounded to the block. Could that cause readings to be reversed? VDO gauge.

I must say that I am not all that impressed with VDO. So far the volt meter and water temp gauges have packed it up. Now this from the oil pressure. Also, at times, the odometer looks like it is sending messages in Chinese.

Bill
Click to expand...



First things first; what does the mechanical gauge indicate the pressure does as RPM increases?

Electric gauges are typically connected in series with the sender (aka, grounded through the sender). Single terminal senders typically connect to ground through the threads. PTFE "plumbers tape" is a good insulator, so .....

Electric gauges and senders are a matched set. If one or the other (or both) is a mis-match or wackadoodle, ......
 
Last edited:
B

Bill Blue

Platinum Level Sponsor
Hi Barry. Just got through doing a varying RPM pressure test. When I did the first test I had no idea this kind of problem could occur. Besides, the mechanical gauge is under the car, so this is truly a two person operation.

Results:
A few seconds after startup, the mechanical gauge never varied out of the 55-60 psi range. This was from about 1200 to 3000 rpm. Dash gauge ranged from 20-10 psi. Really strange, while the pressure went up from about 57 to 60 during a rev up, the dash gauge showed a 10 psi drop from 20 to 10. So I guess we know where the problem lies, even though it makes no sense.

BTW, testing from the sender body to engine block shows less than 2 Ohms resistance. I think that probably as good as can be expected.

VDO says this is THE sender for the gauge. Just crap instruments.
 
Barry

Barry

Diamond Level Sponsor
Bill Blue said:
Hi Barry. Just got through doing a varying RPM pressure test. When I did the first test I had no idea this kind of problem could occur. Besides, the mechanical gauge is under the car, so this is truly a two person operation.

Results:
A few seconds after startup, the mechanical gauge never varied out of the 55-60 psi range. This was from about 1200 to 3000 rpm. Dash gauge ranged from 20-10 psi. Really strange, while the pressure went up from about 57 to 60 during a rev up, the dash gauge showed a 10 psi drop from 20 to 10. So I guess we know where the problem lies, even though it makes no sense.

BTW, testing from the sender body to engine block shows less than 2 Ohms resistance. I think that probably as good as can be expected.

VDO says this is THE sender for the gauge. Just crap instruments.
Click to expand...




It seems fairly certain that (a) your engine has good oil pressure and (b) the VDO oil pressure gauge has joined the volt and water temperature gauges at the wackadoodle cafe.

Too bad about the poor VDO gauge performance; they are one of the few companies that make gauges (including a 4" diameter speedometer and tachometer) that look right in a Series Alpine.
 
P

PROCRAFT

Donation Time
Barry said:
It seems fairly certain that (a) your engine has good oil pressure and (b) the VDO oil pressure gauge has joined the volt and water temperature gauges at the wackadoodle cafe.

Too bad about the poor VDO gauge performance; they are one of the few companies that make gauges (including a 4" diameter speedometer and tachometer) that look right in a Series Alpine.
Click to expand...
Barry, your right about the 4" gauges were using them as to Bills problem we had a similar deal with the oil pressure gauge the guys we got our stuff from sent us a new gauge and sender and before it got here we had solved the problem, I would say Bill has a faulty gauge like you said I traced my problem to the threads that the sender threaded into. kinda like weeping.
 
P

PROCRAFT

Donation Time
And this is the forth car we've used VDO stuff on and have never experienced the problems Bills having. reckon we got lucky?
 
loose_electron

loose_electron

Donation Time
Bill Blue said:
BTW, testing from the sender body to engine block shows less than 2 Ohms resistance. I think that probably as good as can be expected.
Click to expand...

That is a lot of resistance for that connection in my opinion. Subtract out the the resistance of the clip leads and you should hopefully be well under 0.5 ohms. Instruments in pretty much all cars are a horrorshow of accuracy due to the less than optimal designs, but cars have been using these methods for a long time.

I use Speed Hut gauges and senders and have been pretty happy with what I got.
 
B

Bill Blue

Platinum Level Sponsor
I can put up with inaccuracy, I really don't care if the pressure is 40 instead of 50. But I do want consistency.

I suppose most owners would be happy with the VDO's. The car has 108,000 miles on it, I think the problems started popping up at about 50,000. Few Alpines see that many miles on a rebuild. But still, I should not be having these problems. We are scrapping our 2003 Focus with about 275,000 miles on it. It leaves parts behind with every departure, but the gauges still work just fine.

"That is a lot of resistance for that connection in my opinion."

"That connection" is in fact, three connections. That is what happens when you stuff ten pounds of sh!t in a 5 pound sack.

Bill
 
Barry

Barry

Diamond Level Sponsor
There is a lot of "noise" in automotive electrical systems. I am a firm believer in filtering the DC power for anything electronic.
 
loose_electron

loose_electron

Donation Time
Barry said:
There is a lot of "noise" in automotive electrical systems. I am a firm believer in filtering the DC power for anything electronic.
Click to expand...

Huge amount of noise, and a huge amount of power level variance. Both can be dealt with inside the instrument itself (internal filtering and power regulation) in modern instruments. (Industrial, medical, etc) But, best practices in any measurement system is to not include the ground path as part of the measurement. Instruments in cars have been doing this sort of dumb thing forever. Just the EE side of me bitching.
 
Barry

Barry

Diamond Level Sponsor
Modern cars are probably all active filtering / regulation, but a properly designed, old fashioned, brute force Pi or T filter is still hard to beat when it comes to cleaning up trashy DC power.
 
C

Charles Johns

Donation Time
Bill Blue said:
Hi Barry. Just got through doing a varying RPM pressure test. When I did the first test I had no idea this kind of problem could occur. Besides, the mechanical gauge is under the car, so this is truly a two person operation.

Results:
A few seconds after startup, the mechanical gauge never varied out of the 55-60 psi range. This was from about 1200 to 3000 rpm. Dash gauge ranged from 20-10 psi. Really strange, while the pressure went up from about 57 to 60 during a rev up, the dash gauge showed a 10 psi drop from 20 to 10. So I guess we know where the problem lies, even though it makes no sense.

BTW, testing from the sender body to engine block shows less than 2 Ohms resistance. I think that probably as good as can be expected.

VDO says this is THE sender for the gauge. Just crap instruments.
Click to expand...
Bill, Just One reason I prefer mechanical oil gauges. My new VDO (I think) gauges got stolen during the move and I was looking at new ones. Maybe a different brand though. I always had good luck with Stewart Warner...may go back.
 
B

Bill Blue

Platinum Level Sponsor
The new oil pressure gauge is a VDO, but not of the Visions line. Purchased from Surplus Center for less than twenty bucks, bought two of them. Sad to report the water temp gauge packed it up (again), I am now using one of the Surplus Center non Visions VDO temp gauges. Works better than any of the Visions units did. Much more stable. Surplus Center buys a lot of stuff from manufacturers. I am wondering if VDO aftermarket gauges are of a lesser quality than their OEM stuff.

Bill
 
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