Oil Pressure

[jgraff]

Noting that I have seen and heard the comments on the faulty oil pressure gauges, and faulty grounds concerning the sending units.
My question? How much should I trust the stock gauge and the readings I get. Sometimes I get a reading upwards of 45 PSI, but most times, I get a very low pressure reading, or sometimes not at all. I did clean the sender contacts, and that helped a bit, but the oil pressure readings seem inconsistent. Should I be concerned about the oil pump, or are the stock gauges not that trustworthy. I have been driving the car for a few months without any problems, and it sounds fine, but did notice a tappet making a small noise, and wondered how much to trust the gauge.


Thanks, Jack

[papajam]

If 45 psi is the highest reading you get, even with a cold engine, I'd do some investigating whether or not the oil light comes on while driving (does it come on?). Check the pressure with a known accurate mechanical gauge while driving. You should have 50 psi minimum above about 2500 rpm with a hot engine. If you don't, I'd suspect that a crankplug (or two) may have come out. If the pressure is OK, then the gauge sender is probably at fault.

[Roadtrip]

If your gauge readings for similar driving regimes are inconsistant, that sounds like a wire or sending unit problem. Get it sorting out NOW. All the oil pressure low warning light tells you is the the pressure is above 5 psi . . . and 5 psi ain't enough for an engine under torque. You're readings should be consistent.

First of all, tappet noise is not necessarily an indicator of low oil pressure. Alfa's do not have hydraulic lifters. Further, the cams ride in aluminum bearings and survive well on low oil pressure . . . . . but the crankshaft and bearings DO NOT.

If your engine is old, it is likely to have some deteriorated oil pressure which is ok as long as it's not extreme. Here's some quotes from the 74 Owner's Manual:

page 29:

"Check the oil pressure gauge from time to time and stop the engine if the pressure with a hot engine and at maximum revolutions should fall below limits shown on page 60.

However, if is possible for the warning light to come on when the car is cornering: this may be caused by a low level of oil in the pan which can be easily remidied by topping up.

No trouble exists if the warning light comes on while the engine is idling, especially when hot."

page 60:

"Oil pressure with hot engine - psi

Engine idling minimum 7 psi

Engine running fast minimum 50 maximum 65-70"

I love the maximum expressed as a RANGE.

Soooooo, in plain "non-lawyer weasle mouth" talk, what I deduct from that is:

Minimum 50 psi at 5800 rpm
Oil low pressure light ON at hot idle is ok (light comes on at spec of 5 psi)

To which you ask . . . Maximum rpm? Yes, I lived in Italy for 2 years in the 70s driving the autostrada. It was common for Italians to drive their small engines at maximum, or close to maximum rpm for hours on end. Alfa knew this and designed the engine around it.

Practically speaking, Alfa engine will survive ok on lower running pressure, but personally, getting below 30 or so at U. S. highway running speed is a cause for kicking in a few more bucks into the engine overhaul fund and start ordering parts. Also, I think the same can be said if you're getting an oil pressure low pressure warning light at not idle . . . . regardless of what the book says.

Papajam's recommendation of 50 psi above 2500 rpm is a good one, although I wouldn't panic if it was a little lower, but like I said before, you should be considering a couple weekends of overhaul time.

Do a search on this site for crankshaft plugs, which while isn't COMMON, isn't unheard of either. Symptoms are usually a SUDDEN loss of oil pressure. Pressure will be marginal COLD, but rapidly deteriorate as the oil heats up and becomes less viscous . . . probably zero at idle. That's an mandatory shutdown of the motor until repairs are made . . . . that is unless you'd like to replace a real expensive crankshaft.

Sorry for the ramble. Dinner's taking a little long and I'm on my third glass of wine.

[jgraff]

Thanks Guys,
Upon closer inspection of the gauge, I noticed that it does respond from 0 to about 20 PSI when starting the motor cold. Then it fails to register in relation to the change in engine RPM's or when motor is fully warmed up. Thus, I suspect a bad sending unit. But, in light of the information you have provided, I will be performing a mechanical pressure check, along with the replacement of the sending unit, and maybe the addition of an aftermarket oil pressure gauge which I have been considering anyway. I will get started as soon as my visiting parents relingquish the car which they refush to give up while here on the island. They say it is too much fun to drive around and I can just wait until we have a rainy day. And the oil pressure light does NOT come on while driving it. I have seen it light up momentarily when starting a cold engine, and it is good to know that it is working.


Aloha Jack

[Roadtrip]

Jack - Did this happen like all of a sudden? If so, I seriously doubt it's the gauge, but try and confirm it. Your symptoms sound like a classic lost crankshaft oil plug. You may need to remove the bottom sump plate and search around for an aluminum plug. If you find one, you've got some work ahead of you.

See thread:

Oil pressure guage not working

[jgraff]

Thanks John,
Honestly, I inherited the car about a year ago from a friend who just couldn't devote time or energy towards it, and didn't have a place to keep it. Soooo, I have been slowly working my way through it, i.e. new rag top, center bearing, and U joints, minor electrical, etc.
So, the Oil gauge never really satisfied my interest whenever I was looking at it, but I never cleaned the sender connection until recently, and then I actually was able to see some movement, where previously it was intermittent. So, not having driven it a lot, I don't have much in the way of a history of readings. I have driven it enough though, that if there really was a serious low pressure, I would think I would have already been on the side of the road, so I wouldn't classify this as sudden, just a better education on how well to trust the gauge.
I appreciate your input, as everything is an education which contributes to the finished project.

Aloha Jack

[il_formaggio]

I don't remember exactly where I read this, but easy and worth a try. Start the car and warm up to operating temp. Maybe take a short drive. Shut off the key and immediatly turn the key back on to "run" but don't start the engine. Note how long it takes for the low oil pressure light to come on. If the light comes on instantly there might problems in the lower end. I've only experimented with this on my car, light stays out for maybe 5-7 secs. Maybe some others could try it and see what results.

[Roadtrip]

Jack -
Why don't you test your gauge to be sure it hasn't gone south. All you have to do is take the lead off the sending unit and ground it. The gauge reading should go all the way FULL scale. If it does, then the gauge unit is probaby good. If it is good, you could change the sending unit (about $35) and check the pressure again, or get an inexpensive direct pressure gauge and confirm the reading. In this case you'd have to get an adapter that will screw into the block. That may be a problem trying to find one locally in Maui.

Assuming that the oil pressure really is low, then I think your next step is to remove the very bottom plate of the oil sump and see if you've got any aluminum plugs in there. You may need to reach up a bit on the high part of the sump to make sure there's not one hiding up there as well. If you find one, it might be able to be fixed with the engine in-situ. It depends on which one came out.

Sounds like you're learing alot about Alfas. Keep it up and you'll have a really nice reliable Alfa when you're done.