tnz5106

This original thread became convoluted so I thought I would start a new one. After changing my oil sending unit with a new one, and a fresh oil change with 10w30 synthetic. My low oil pressure got worse. It went from 2-5 psi at an idle (hot), to zero!! I finally just drove the car for about 20 miles and the oil pressure dropped to zero at anything below 2k rpm. Once again, the engine sounded great. Normal oil temp, coolant temp, and no lifter or top end noise.

After I got home, I removed the double bladed plug to the oil sending unit and guess what. The digital readout on the dash read the same as when I had it plugged in. 15-20 psi while revving the engine and zero at an idle. Has anyone ever gotten erroneous readings from the dash. I always thought they worked or they didn't. I am getting ready to hook up a manual oil pressure gauge just to see what I get. I suspect to have normal psi from the manual gauge.

This really puzzles me though as far as the digital readout............anybody have this happen to them?

WVZR-1

Do you know that you actually had a correct sender installed? I believe you could supply specific resistance values to the cluster to confirm either the function of the gauge or the lack of. Do you have a FSM for your car? You're doing the correct thing NOW and that's confirming that you actually have oil pressure but without doing the work there's not an answer out here on the Internet. You need to check your parts and be able to rely on your findings.

I would imagine there's hundreds of people that could answer yes to your question but likely most couldn't tell you why!

Gauge is likely a 0 - 90 ohm unit and I'd think these are potential values:

10 ohm = 4 PSI, 23 ohm = 11 PSI, 30 ohm = 18 PSI, 34 ohm = 23 PSI, 55 ohm = 50 PSI and 90 ohm = 80 PSI, the warning light should be on at 4, 11 & 18 maybe. Values are +/- maybe as much as 10%. You would use your mechanical gauge and RPM to evaluate.

C409

..... You mention that you unplugged the double bladed connector ... IIRC that is the fuel pump switch ... the large single bladed sender is for the gauge ..........

WVZR-1

I actually overlooked that and that amazes me! BUT I did ask if he had the "correct" sender. Seems the question is now considered answered. No he doesn't!

OP - on your car the gauge sender is the larger bell shaped sender with a single spade terminal.

Like the one in this link:

http://www.ecklerscorvette.com/corve...late-1989.html

tnz5106

Doesn't make sense. I see what you are saying, but the owner of napa mentioned that it called for a single blade sending unit and she would have to order it. I happened to have the car outside so she came out looked at it. She looked at it and I pulled the connector off. She said" yep, yours is the double blade type" it was only 11 bucks so I bought it. When I got home I installed it before I changed the oil to see if it made a difference. It actually lowered the pressure a little bit it seemed. Then I changed the oil and that's when the zero psi at an idle started.

Anyway, guys, it looks like all the oil sending units I have seen, also, why would it be back there where the oil sending unit normally is?

I appreciate everyone's help, and patients with me. I will look closer tomorrow. Also, I thought the gas sending unit was on the fuel rail? Thanks again for your help.........

WVZR-1

This is what you should see at the rear of the engine. This looks to be configured correctly I believe:


http://www.ebay.com/itm/1985-1986-19...-/221257590978

xrav22

10-40 Valvoline conventional and 1/2 can of STP. 155,000 miles stock.


http://forums.corvetteforum.com/g/picture/1556752

WW7

Something isn't right with this Ecklers add , because my 89 doesn't take a single blade sender , it takes the double blade sender..WW

http://www.ecklerscorvette.com/corve...late-1989.html

WVZR-1

'88 is the last year for the single spade bell. '89 is three blade that does fuel pump and the gauge. I paid no attention to their applications, I used the link to show the OP what he should expect. Your '89 also isn't anything like the image. Yours should be maybe 1" cylindrical with an entirely different connector configuration.

tnz5106

I would say you are right. Will I have to take the distributer out to get to it? You know my oil pressure started dropping when I had an oil leak I couldnt identify where it was coming from. I had to replace my starter last year because it was soaked in oil. But the oil was not coming from the valve cover or the intake. I just bought another kwiklift so I can get under the car easily. I am going to look and see if all this may be connected. I will continue to investigate...........thanks very much.

tnz5106

Last weekend after not believing that my oil pressure was that low, I drove the car on a 175 mile round trip. Engine temp stayed 190-206 degrees. Low Oil pressure light stayed on most of the trip. Engine ran strong and sounded great all night. Tuesday, I took the car to a local mechanic I know and told him to install the new correct oil sending unit "single blade", I also told him to check the oil pressure with a manual gauge first. He calls me at work the next day and says with the manual gauge, he was getting 25-30 psi at idle and 40+ when he revs it up Great new right? Ok, I told him to go ahead and install the new sending unit, flush the coolant system, replace the rubber engine oil cooler lines, and new brakes on the front.
Today he calls me just before I was going to pick it up, being excited like a kid for 2 days thinking everything is ok now and looking forward to a road trip tomorrow. He says that when they used the manual gauge the other day, the engine was cool, and they didn't let it warm up!! Guess what, the damn oil pressure is still at zero!! He told me that the napa syn 10w30 was too thin and he suggested conventional 20w50. I told him that some of the guys on the forum use that and to go ahead and change it. I go and pick the car up a little while ago and the oil pressure is still 6-15 psi from idle to 2500 rpm engine temp 200 degrees. The red light comes on at anything below 8psi. Now when I rev it, the psi moves very slowly. Anyway, He told me " Your old 147k miles engine is just worn out"!!!!!!
I just can't believe it. It sounds great, runs great, so what is going on?? We know 2 things now. The oil sending unit is functioning properly and so is the dash. Should I try another weight of oil? I know its something we are overlooking.......any ideas?

tnz5106

The mechanic put the manual gauge back on today with the engine oil hot. That's how he verified that the pressure was low. But guys, no engine can survive with this low of pressure. I owned my own auto machine shop in the '80s, and vatted and prepped many of small block Chevys. I remember how the oil routes from the filter to the port by the distributor, and is the pressure is low up on top of the block, its low on the bottom, and with pressure that low there is no way an engine could survive!! What is going on here? I plan on driving the car over 100 miles tomorrow. Should I not?

jake corvette

I dunno what might be happening here but for peace of mind, I'd pull the oil pan and install new bearings. Use Plastigage to check the clearance of the new bearings. Not much money involved and as long as you are under there, replace the oil pump and check the pick-up tube to make sure the screen is not plugged as well. You just know that you are going to drop the oil pan sooner or later, might do it now and get it over with.

Unlike some others on the forum I use high volume pumps. High volume pumps do not provide higher volume at higher engine speeds but they only push more oil until the pressure relief spring in the pump opens and diverts the excess oil back to the inlet side of the pump itself. High-pressure pumps are another story.

Just what I've done over the last fifty years - -

Jake -

DanZ51

Just by chance, did the mechanic change out the filter when he changed weight oil? I only ask this because my oil pressure read wonky a few years back with a cheap (Fram) filter on it (scared the crap out of me too). I changed the oil and filter, and all is back to normal. I can't explain it and I didn't really bother to investigate it further. That was like three or more years ago and never had any more oil pressure reading issues ever (knock wood).

tnz5106

TTT.......need some more opinions guys. Just got back from a 120 round trip to Chattanooga. At 200degrees engine temp most of the trip, with the fresh conventional 20w50 oil pressure stayed between 4-6 psi at idle to 7-9psi cruising at 65 mph. At least it never went to zero like it did before!! I pulled the oil cap off the passenger side valve cover and put Ina pint of additive. As I looked down in the big 21/2 in opening, there was plenty of oil on the rocker arms and some pooling. Looks like plenty of oil to me.

I know guys, I am trying to postpone the inevitable, an engine overhaul. But she sounds and runs so sweeeet!! With that low of oil pressure, how can it stay together?

WVZR-1

Ask your mechanic friend how much to just put bearings and an oil pump in it!

cudamax

Went on a 200 mile trip anyways with the oil pressure going down to Zero and u start another thread after all the advise that was given to you on the first thread
Damn I'd say it's time to go on a 400 mile trip now. You agree. You got one planned. You ask for advise but don't listen at all or take any.
I'd say wait go on the trip and stop at any Drag Strip u see too and run it for at least 10 runs back to back Reving it to 6500 rpm

jake corvette

tnz - hmm - this is interesting.

Is your engine noisy - rod bearing noise or lifter clatter? With the oil pressures that low, I'd expect a lot of noise from both. If things are quiet - then it seems like the engine does in fact have good oil pressure, even though it appears low at the pressure port.

Any foam in the oil by the rocker arms? Any chance the pump inlet is sucking air or cavitating - clogged inlet screen perhaps? Overfilled oil pan allowing the crankshaft to make contact with the oil itself? Again foaming conditions.

Did you actually witness the oil pressure reading on the mechanical gauge or are you relying on what the mechanic said? Might be prudent to check the pressure once more, again with a mechanical gauge – using a different technician or shop. Someone may be trying to sell you an overhaul that you don't need.

Is the pressure being taken directly off the block or is there a "Tee" in there someplace? The Tee might be clogged - a long shot

Something is not making sense here – Don’t understand all that I know- LOL!

Just some thoughts- -

Jake -

xrav22

Tuesday, I took the car to a local mechanic I know and told him to install the new correct oil sending unit "single blade", I also told him to check the oil pressure with a manual gauge first. He calls me at work the next day and says with the manual gauge, he was getting 25-30 psi at idle and 40+ when he revs it up Great new right?

Am I reading this correctly he checked it with a manual guage it was OK. Guys he needs to find why the guage is possibly reading wrong. Mabey a frayed wire , dirty connector, dirty pins at dash connector. My dash pins were dirty but it did not affect my oil pressure guage. What would cause a low reading, I know disconnect it and it reads high (80). Good Luck

3JsVette

Could the problem be in the dash cluster?
I had the same thing happen on my '85 and shut the thing off immediately. I checked the oil level and it was full. I started the engine no noises at all. I then noticed the gas gauge was doing the same thing, It was reading almost empty and I knew there was over a 1/4 tank. I drove home with no problem but I haven't had a chance to check further.