with this 100%
Oil Filter Bypass Valve
Thread Starter
Advanced
Joined: Aug 2013
Posts: 63
Likes: 1
Oil Filter Bypass Valve
Can the bypass valve be replaced in a 86 Corvette L98 base?
The FSM says that the valve and adapter must be replaced as a unit. Does anyone sell this unit or just the valve?
My C4 has low millage (34,000 mile garage queen). My oil pressure dropped suddenly to 39 PSI hot at 70 MPH and 14 PSI at idle. It was in the 50's and 60's. I have not valve train noise.
I first thought it was the sender. I replaced it with the exact same results. I do not want to install a mechanical gauge.
The FSM says that the valve and adapter must be replaced as a unit. Does anyone sell this unit or just the valve?
My C4 has low millage (34,000 mile garage queen). My oil pressure dropped suddenly to 39 PSI hot at 70 MPH and 14 PSI at idle. It was in the 50's and 60's. I have not valve train noise.
I first thought it was the sender. I replaced it with the exact same results. I do not want to install a mechanical gauge.
Race Director
Joined: Oct 2008
Posts: 17,982
Likes: 1,074
From: Lansing MI
If there is even a problem then it would be related to the oil pressure relief valve. This is part of the oil pump. I would verify with a mechanical gauge what you think the electrical gauge is telling you. Personally I don't think 40 psi is all that abnormal.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
You mention "base" so it's assumed you don't have the oil cooler/heater option. Is that correct? If that's correct just buy the filter mounting adapter and give it a try. Very straight forward install for sure. A "fix"? Likely not but if it's reassuring then "just do it". The adapter by-pass isn't a control device that offers up visual changes in pressures.
***I'd think maybe a sump/pick-up issue maybe more likely - you could respring the oil pump if you wanted and attempt that also OR you could just do the pump! The spring (relief/regulating)) in the pump could be purchased separately. Still available? Don't know - it was the same as many GM applications in many other engines.
*** I meant to mention and forgot - there's much that needs considered. Is this a higher mileage untouched original engine? A higher mile that's been maybe been thought to be "rebuilt" or had internals serviced? You might consider supplying "known resistance" to the gauge and confirm it's accuracy at advertised resistances. It's all in the FSM I believe.
***I'd think maybe a sump/pick-up issue maybe more likely - you could respring the oil pump if you wanted and attempt that also OR you could just do the pump! The spring (relief/regulating)) in the pump could be purchased separately. Still available? Don't know - it was the same as many GM applications in many other engines.
*** I meant to mention and forgot - there's much that needs considered. Is this a higher mileage untouched original engine? A higher mile that's been maybe been thought to be "rebuilt" or had internals serviced? You might consider supplying "known resistance" to the gauge and confirm it's accuracy at advertised resistances. It's all in the FSM I believe.
Last edited by WVZR-1; Jun 6, 2016 at 09:37 AM.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
Were it mine and I wasn't concerned with originality but instead "reliability" I would likely remove the heater/cooler as required then add the base filter adapter and move on. You still have to confirm the gauge, your new sender likely against a mechanical but I see no reason to retain the heater/cooler for other than "originality" purposes. That's your decision !!!
Melting Slicks
Joined: Nov 2010
Posts: 2,216
Likes: 113
From: Michigan
They make non-bypass oil filter adapters or you can mod yours(google it), but if your filter has a bypass and some do then it's the same thing.
edit: Not to be used in cold weather the oil will be too thick.
edit: Not to be used in cold weather the oil will be too thick.
Last edited by BOOT77; Jun 6, 2016 at 01:21 PM.
Team Owner
Joined: Sep 2003
Posts: 20,179
Likes: 673
From: Freedom is never more than one generation away from extinction.
St. Jude '03 thru '24
My 86 has 100K plus. The oil pressure is as you have indicated using Mobil syn.
Rule of thumb for oil pressure is 10 PSI for each 1000RPM.
Rule of thumb for oil pressure is 10 PSI for each 1000RPM.
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Safety Car
Joined: Sep 2004
Posts: 3,953
Likes: 550
From: Mission Viejo CA
Team Owner
Joined: Jul 2004
Posts: 28,474
Likes: 3,291
From: Hartford WI
Thread Starter
Advanced
Joined: Aug 2013
Posts: 63
Likes: 1
The bypass valve has nothing to do with your oil pressure. Its only purpose is to allow oil to bypass the oil filter if the differential pressure between the inside and the outside of the oil filter element exceed its rating. This might be caused by poor maintenance (clogged filter) or extremely thick motor oil (-40* environment). Neither of these is likely! Even if your bypass valve were stuck open, you'd never know it unless you would dissect your oil filter after many, many miles, and find that it was like new!
I am concerned that the valve has malfunctioned with trash under the seat or broken spring. I plan on inspecting it. I just wanted to know where to find one if it proves defective.
Safety Car
Joined: Sep 2001
Posts: 4,157
Likes: 554
From: Glenbeulah Wi
It is my understanding that the bypass valve directions flow to the filter back into the oil pan if pressure is too high OR if it is malfunctioning. Oil pressure is measured downstream of the filter. How can it not have an effect on oil pressure indicated if part of the stream is bled off back into the pan.
I am concerned that the valve has malfunctioned with trash under the seat or broken spring. I plan on inspecting it. I just wanted to know where to find one if it proves defective.
I am concerned that the valve has malfunctioned with trash under the seat or broken spring. I plan on inspecting it. I just wanted to know where to find one if it proves defective.
Last edited by bjankuski; Jun 6, 2016 at 04:45 PM.
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
I understood the engineering and understand HRR/others comments. I mentioned the "just do it" since the OP felt he wanted to and it's as simple as a filter change and cheap BUT THEN he complicated it with the mention he has the heater/cooler. Certainly makes it more difficult!
If he does it he convinces maybe himself!
He could have done some fairly straight forward diagnostics before ever doing his 1st replacement of the sender!
If he does it he convinces maybe himself!
He could have done some fairly straight forward diagnostics before ever doing his 1st replacement of the sender!
Melting Slicks
Joined: Jan 2014
Posts: 2,192
Likes: 381
From: Lunenburg MA
The odds of it being an electrical gauge problem in your 30 year old queen are probably 10X the odds of it being a mechanical one. Especially if you have no other symptoms such as noisy lifters.
Race Director
Joined: Apr 2003
Posts: 17,700
Likes: 1,667
From: moraga ca
Reading the op's original post, I don't think there is a problem at all. Oil pressure isn't normally 50 or 60 psi while cruising when the motor is hot. Maybe this was before the oil temperature was at operating temperature or maybe the op was mistaken. There is nothing wrong with 30 psi at 2000 rpm with the engine warmed up.