Chalkboss

A little history, 87 S4 w/85K on the clock. Filled with 15-50 Mobil One. Due to a low idle oil pressure (1 to 1.5 bar warmed up) I replaced the oil plugs in head. I found one that had popped out of the head on the drivers side. Put the metal pins in (5), did the fuel lines, and everything was great for the first 30 miles or so. I had excellent idle oil pressure (2.5 to 3 bar).
Went on a 250 mile drive and low and behold the oil pressure dropped to around 1 bar at idle and the ! flashed. Above 2K I get 4-5 bar. Checked the oil level, fine. Engine sounds good. But my oil pressure gauge needle is acting wacky. Sometimes it jumps up briefly to 5 and then shakes around 1-3. I am thinking it is the sending unit. Any advice?

Bilal928S4

Replacing the sending unit would be the cheapest fix.

Speedtoys

Ya..gunk in the sending unit. although with enough of the right fittings, etc, I imagine one could run solvent in/out of it with the help of a vacuum pump and clear er right now.

But they are cheap to buy as well...just schedule an oil change to replace it, easier with the filter out.

fraggle

Speedtoys, your avatar freaks me out. A lot.

Bilal928S4

You do not want to think about the other option, which is that you did not R&R the pucks properly and one let go.

IcemanG17

not the sending unit...its the oil thermostat above the sending unit....the two springs that control when the oil cooler is open fatigue over time..... Replace both springs and clean the center unit....so you will need the two springs (one short one long) and the seal for the sending unit....its a bit of a PITA to do, since you need a special short wrench to get it off....I took the whole thing off as a unit from the block, then seperate teh sending unit if you need to later

ROG100

On every car I have replaced the thermostat and springs on it made NO difference what so ever.
Try the sensor first.

depami

Don't buy the cheap one. I did and regret it. The PSI sending part works fine but the low PSI switch part is erratic.

Now I need to buy the more expensive one anyway.

Rog, are these on your Christmas sale list?

Avar928

http://members.rennlist.com/v1uhoh/oilp.htm

Here's a guide. Gunk can accumulate inside but more importantly it can build up on the connectors and wiring.

Try to clean up the old VDO sender. The cheaper FAE one is okay but requires you to either change the female connector or male end on the unit because one they're different sizes. If you do that, the plastic protective boot won't fit.

The sender unit is on pretty tight and requires an adjustable wrench or a very thin one and I think a 27mm to counter hold.

depami

I would not buy that one. I currently have the warning light wire disconnected because the FAE switching point is so inconsistent.

Avar928

Yea, I'm thinking of replacing mine with the old VDO actually. I think I got the wires hooked up the right way the first time, I could not for life of me discern what the markings on the FAE sender meant. Couldn't tell which was ground or what not so I just hooked it up and prayed.

The FAE sender is indeed wonky. Going to check the connections again. I swapped out the male connector so I wouldn't need to do anything to the wires but the fitment was a bit loose.

Chalkboss

Thanks for the advice. I will try a oem sender first, then go from there. It looks like it is leaking and original so can't hurt.

Avar928

Clean it up before dropping close to $100 on a new VDO unit.

I had a coolant leak that basically steam cleaned my underside while I was driving and it loosened up enough grime to make my oil pressure readings work. It was intermittent until I dived back in but it worked.

z driver 88t

On my car it was a faulty sending unit. Same symptoms. Low oil pressure at idle, ! Light would come on. Revved engine and pressure would bump up. Sending unit was an inexpensive first try based on my history with old Z cars, also prone to sending unit issues. Replaced sending unit, problem solved. YMMV.

Chalkboss

It was a faulty sending unit. Replaced and pressure now 3 bar hot idle and 5 off idle. Thanks for the advice and now I can relax until the next issue!