C4 Question

Reply Subscribe

Thread Tools

Search this Thread

Mar 22, 2015 | 09:34 PM

NearyJr

Thread Starter

Cruising

Joined: Feb 2013

Posts: 12

Likes: 0

From: Ringoes NJ

C4 Question

Question to the C4 gang. 1985 with 35,000 miles in great shape. I bought it 2 years ago and the previous owner replaced the oil pressure sending unit due to a leak a year before he sold it to me. In December the oil pressure gauge stuck at 80 psi. I bought a new one from Corvette Central put it on and it worked for about one minute. At idle it was showing between 47 and 51 psi. I slowly increased the throttle and the psi climbed accordingly. When I got to over 3,000 rpms the gauge went to 80 psi and got stuck there again. Any ideas as this one puzzles me and I really don't want to replace another one of those things ever again.

thanks,
Fred Neary

Mar 22, 2015 | 09:40 PM

FASTAZU

Race Director

Joined: Feb 2002

Posts: 11,592

Likes: 1,053

From: Compound in the Grove, Ga.

2026 Corvette of the Year Finalist - Unmodified

2025 C4 of the Year Winner - Unmodified

2024 C4 of the Year Finalist - Unmodified

2020 C3 of the Year Finalist - Unmodified

2019 C4 of Year Finalist (performance mods)

2018 C4 of Year Finalist

2015 C4 of the Year Finalist

St. Jude Donor '16

I would get an oil pressure gauge and hook it up just to be sure your ok, than track down whats up with the sending unit/s may be an electrical short. (just a guess)

Mar 22, 2015 | 09:46 PM

HAD2HAV2

Melting Slicks

Joined: Jan 2001

Posts: 2,996

Likes: 303

From: MOORESVILLE NC

You need to have the oil pressure measured by a mechanical means to be safe. Then you can find the electric gremlin.

Mar 22, 2015 | 10:00 PM

1984Z51auto

Pro

Joined: Jan 2003

Posts: 706

Likes: 47

From: Denver Colorado

High Oil Pressure??

The two responses you already have are right on. You need to be sure of your oil pressure prior to digging into the electrical side of things. A mechanical gauge reading is the best way to do that. The Chevy small block has a pressure regulator as part of the oil pump. It is a spring with a cup held in place with a pin. The spring acts as a pressure relief to limit the pressure. They can stick and not limit pressure. If your mechanical gauge reading is very high that is "probably" the issue. Sooo you then get to pull the oil pan and replace the 30 year old pump

Mar 22, 2015 | 10:45 PM

antfarmer2

Race Director

Joined: Mar 2015

Posts: 15,926

Likes: 578

Quote:

Originally Posted by 1984Z51auto

Mar 22, 2015 | 11:28 PM

gerardvg

Safety Car

Joined: Aug 2009

Posts: 3,745

Likes: 275

From: Melbourne, Victoria, Australia

Hi

See the link below, can you confirm that is what you replaced (the oil pressure sending unit). Yes a real pain to replace behind/beside the distributor on the block.

The smaller one with two prongs is the pressure switch.
There is also an oil temperature switch above the oil filter.
The oil pressure sending unit should have no problem with 80 psi, my 85 with high press/ high volume oil pump gets to 80 psi and back without a problem.

http://www.ebay.com/itm/Engine-Oil-Pressure-Sender-With-Gauge-Standard-PS155T-/221262713369?pt=Motors_Car_Truck_Parts_Accessories&fits=Year%3A1985%7CModel%3ACorvette&hash=item3384491219

Mar 23, 2015 | 12:39 AM

Cliff Harris

Race Director

Joined: Apr 2002

Posts: 10,036

Likes: 346

From: Anaheim CA

I have heard that if the connection to the oil pressure sender is open the gauge will read 80 PSI. You might have a bad connection in there somewhere.

Mar 23, 2015 | 10:41 AM

NearyJr

Thread Starter

Cruising

Joined: Feb 2013

Posts: 12

Likes: 0

From: Ringoes NJ

Thanks to all of you who responded to my question and I am going to take the car to my mechanic for the proper testing. This forum is great for novices like me who are not mechanics but try to turn wrenches for fun (when I can't do any real damage!). Replacing that oil pressure sensor was the hardest thing I've tried yet.

Thanks to all again,
Fred