Hello, I just got my first corvette (1990 auto) and its great apart from I noticed the oil pressure is seriously low at idle when warm. It runs in the hatching.
Now Claremont corvette (dealer) was selling this car recently at £12000 GBP and its only done 57K miles and appears mint inside and out apart from this pretty major glitch. Another local corvette dealer has advised that its likely bottom end wear from a previous owner running the engine low on oil at some point and an bottom end rebuild is the future answer. Not what I wanted to hear as I've spent all my money (and then some) buying the car I've always wanted. Its my daily drive and I need reliability!
Anyway, the dealer told me to change the oil for 20/50 and also put in a can of Wynns oil additive to help coat the bearings and hold better oil pressure. The engine is now holding better oil pressure - and oil pressure is absolutely fine under any gas whatsoever, its just still much lower than it should be at idle.
What is involved in a bottom end rebuild? I was quoted £2000 GBP from Dart Corvette which I suppose is about 3500 dollars at the current exchange rate.
In support of the dealer he told me not to stress and that the engine will likely do another 40-50K miles no problems, but its worrying me.
Any advise?

 

What was the pressure? If you know a GOOD mechanic he might be able to put it up in the air-pull the pan and put in new rod bearings-without having to pull the motor. I've done that before, but if it's burning oil it maybe time for a rebuild.

 

Hi Rick, pressure was in the hatching at bottom of gauge (with 10/30 oil) when warm- now its on 20/50 its maybe just under a quarter from bottom now at idle. With any pressure on the throttle at all it runs maybe a 3rd of the gauge. Doesnt seem to burn oil, but as I've only owned the car 2 weeks its a bit early to tell. I will keep an eye on it.
thanks for your feedback.

 

And it could be nothing more than the gauge is reading low. Easy to check that one.

 

My 87 with 102,000 miles on it at 180 operating temp idles at 30 psi
and cruising 58 psi. These small block chevies can run for years with
less oil pressure-BUT, I'd want to know what's up. Could be the oil
pickup screen is blocked from lack of proper oil changes, sometimes
the oil pick up tubes have actually dropped off-the better ones are
tack welded, could need a new oil pump or even a sending unit,
worse case new bearings. I'd still want to pull the pan and check
things out-even pull a rod bearing and have a look. Going with
a thicker viscosity oil may just be masking the problem. Good Luck.

 

At idle, 1/4 ways on the gauge is normal. On my 89 at idle in drive, 180 degrees mine is around 15-20. At 200 +degrees it can drop as low as 11-12 lbs, dont worry about it. These only need 10psi/1000 rpm to live. In fact, i dont think Ive ever seen 50 lbs on my readout, and I track the car occasionally. SBC have a great oiling system.
Enjoy the car.

 

I am with the gang on this one. I don't think you have anything to fret.

The SBC has a great oiling system and works very well.

If you are concerned, cut the oil filter open and inspect it for metal. If there is shavings, then you know your hosed.

Was this car a recent US export? Or had it been in GB for a while? If it was recent, it would have Carfax data on it, mileage reporting and such.

However, it is a sad truth that Corvettes do not hide their mileage well.... so a repaint and a renewed interior is the only way to cover it...

 

they have a great oiling system-fact when I adjusted my solids on my 64 oil would shoot over the fender, 64s were not clam shells, and he's correct about lasting for years with much lower pressure-I have twin 350s in my boat-which runs 2000-3500 RPMs
mostly and oil pressure on it at 180 is around 25 psi running 40 weight-but with 1500 hours on them they're tired. If my vette ever gets to where his is-12 psi-I'm going in. Not to say it won't last-it's just not typical for a sbc to have low pressure like that, unless something is bad or going bad.
The cutting of the oil filter is a good idea-but a clogged pick may not have caused any bearing damage. It could be as simple as that or even a defective sender.Me-I'd just want to know.I think my oil pressure is more typical of a well maintained sbc.

 

How do you know that your oil pressure is low? What IS your oil pressure? Factory, analog, gauges are notoriously inaccurate. I have yet to see any books that reference, "in the hatching" as good, bad or indifferent, relative to oil pressure. Step one! Hook up a known, accurate, mechanical, oil pressure gauge, and see what your oil pressure really IS. Once you know the oil pressure, you can make an informed judgment, as to whether it is too low, or not.

RACE ON!!!

 

I am assuming you have no knocking noises from your emgine, from your bearings (same speed as engine RPM) or your tappits or camshaft (twice engine RPM) or you would have reported this. Do you?

The stock guages are notorously inaccurate or you may have a bad oil preassure sender. Hook up a mechanical guage where the stock sender is screwed in at the back of the intake and find out what the preassure really is at idle.

My 1992 LT1 factory service manual says that minimum oil preassure should be:

41.4kPa (6.0 psi) at 1,000 RPM
124.1 kPa (18.0 psi ) at 2,000 RPM
165.5 kPa (24.0 psi) at 4,000 RPM

I would be amased if your engine does not meet these minimum standards when tested with a mechanical preassure guage.
If the guage is reading incorrectly you probably only need a new oil sender.

If your engine is not telling you there is low oil preassure by knocking at a bearing or lifter you do not have lower than minimum oil preassure.

If there is no knock it is far more likely that you have found out what every new Corvette owner soon finds out. The dealership and technitions all think we are rich people and they set out to steal our money.

If there is a knock you should do as suggested and remove the oil filter and cut it to see if there are any metal bearing shavings trapped in it.
How did the oil look when you changed it? Were there any metalic particles in it? If not you do NOT have bad bearings.

Get yourself a Factory Service Manual and start educating yourself on your car and doing your own wrenching, you will save yourself a bunch of money. These cars are very reliable and you can fix most things with the help of this forum.

Oh yea ... welcome to the forum, good to have you here.

Hope this saves you some money.

Jerris

 

Thanks for all the great feedback guys, I really appreciate it. I will try to answer some of the questions you have asked me.
1. It was running 10/30 oil and I have to admit I didnt check for any metal particals or anything. I'll do another oil change shortly and take a look!
2. Shortly before the oil change previous to my buying the car it had an engine flush. Many people say engine flushes do more bad than good.
3. Engine does not knock or tap - top or bottom end. Idle is a little "surgy", i.e. not perfect, but hey what is?
The car drives beautifully, and certainly seems to have enough power (I had an LT1 Transam prior to this) and the L98 block seems more than equivalent in power.
4. Car was originally a Japanese car - its a Euro Spec vehicle. Imported into the UK 4 years ago the previous owner has spent loads of money on various electrical bits (ECU, fuel pump, etc), pipes, hoses, belts etc. Also, as this car was being sold by the "premier" corvette dealer in the UK and one of the most respected in Europe, I foolishly didnt fine tooth comb the engine!
5. The "in the hatching" comment comes from the owners handbook, which pretty much says if gauge reads in the hatching, you are in deep poop!

Even at idle, oil is getting to the top of the block, so I will take the advice of the majority and just enjoy the car for now. Its a relief to hear consenting opinion. I will also try to get a mechanical oil pressure test done to set my mind at rest.
Cheers again!

 

dead nuts on

by the way, the 90 guages are among the worst in terms of accuracy.......its the first C4 year that went with analog and the term notoriously inaccurate is.....quite accurate