oil pressure light pulsating on and off

[1972BlueC20]

It's done it twice now in the past week. My oil pressure light on the dash will come on randomly, both times the truck is at full operating temperature....the light will pulsate or kinda flicker. The oil is full. I have a new oil pressure switch too already.

I'm running a fram filter. I know now that these are horrible filters after reading this site. I won't use fram anymore. I'm about to change the oil this weekend anyways. I'm going to use a Napa gold filter and 10w 40 valvoline.


Do you think the fram could be causing my issue?

[trac209]

I've used nothing but fram most times never had an issue. You're going to have to put a gauge on it to see if your oil pressure is low. Chances are if it's doing it only warmed up your pressure is dropping to less than 5psi at idle which is not ideal. A gauge is the only way to see what's going on.

[Shaky]

Fram used to make good filters. Then Allied Signal bought them and cheapened the heck out of them. Most motorcycle race tracks will specifically not allow you to run a Fram due to problems they've had with them puking on the track.

Search around the internet and there's some cut-up comparisons of oil filters. I'll run anything but a Fram.

How many miles on the engine? Does it only happen at idle? Do you have a high volume pump (sometimes they move too much oil)?

[1972BlueC20]

Engine has 84k miles. It only triggers the oil pressure light at idle. Hasn't done it when driving. Just got my transmission rebuilt and the light came on for the first time ever on the way home from picking my truck up from the trans shop. Not sure if they could of bumped something or whatever during the removal and reinstall of the tranny, I wouldn't think so but....

[hamjet]

Originally Posted by 1972BlueC20

Engine has 84k miles. It only triggers the oil pressure light at idle. Hasn't done it when driving. Just got my transmission rebuilt and the light came on for the first time ever on the way home from picking my truck up from the trans shop. Not sure if they could of bumped something or whatever during the removal and reinstall of the tranny, I wouldn't think so but....

This may have been a problem all along, you just didn't notice it because you may have had your idle a little high. They may have adjusted your idle lower than what you had after installing your new rebuilt tranny. (automatic, right?)

[1972BlueC20]

Yes automatic. It doesn't seem like the idle is any different. They didn't say anything about adjusting the idle. Would they normally mess with that when rebuilding a transmission?

[Lee H]

Don't think the filter is causing this. What weight oil are you running? In your neck of the woods I'd be running straight 30W. I would hook up a mechanical gauge and check it.

[JJLT1]

check it with a good quality gauge to know for sure.

the wire could be lightly grounding out on something also??
or the wrong switch??

[1972BlueC20]

I'm running valvoline 10-40

[geezer#99]

THey'd need to remove the kick down linkage at the carb. Could have changed your idle then.
Turn it up a bit.

[1972BlueC20]

So if they did change the idle, do you think they would of made it idle higher or lower? And if this is causing the low oil pressure at idle issue do I just increase the idle to correct?

[geezer#99]

Experiment.
Turn it up.

[kwmech]

Twice had the same customer come into the shop with a very similar problem. He swore by Fram filters, been using them for 40 years, and did his own oil changes. Both times I replaced it with a Wix (NAPA gold) and the problem went away. This was on a big block. The Frams are crap, buy a filter that cost more than 3.00

[1972BlueC20]

Yeah I think I'll get me a mechanical gauge tester and check my pressure. Then I'll do an oil change using a Napa gold filter. I'll also try to get a straight 30 weight oil. Hopefully this will keep the dummy light off. What should my pressure be at idle?

[Lee H]

There's no magic number. Pressure is determined by the rod and main bearing clearance. Fresh motor with tight bearing clearance the pressure is higher, older motor with lots of miles the pressure can be lower. Well seasoned Chevy small blocks are known for lower oil pressure at idle. Is your motor using/burning any oil?

[1972BlueC20]

Nope, not using or burning any oil.

[Lee H]

OK, If it were mine I'd check the sensor connection, check oil pressure with a mechanical gauge, run straight 30W, good filter, and not worry about it. It does not get cold enough in Houston to "require" multi-weight motor oil. What idle RPMs are you running?

[1972BlueC20]

Cool deal. I'm not sure on the idle rpm's. I have a no gauge dash. Just has Speedo, and gas gauge

[Lee H]

No worries, if it idles fine, and does not die when you put it in gear your probably good to go. I'm sure the trans shop adjusted it if it was off to much. Please report back with your mechanical readings at operating temp, at idle and out driving around.

[1972BlueC20]

How would I route the cable for a oil pressure gauge from the engine bay into the cab? Also if I'm going to do that I might as well run a temp gauge too. Where does the temp gauge hook up to on the engine? Sorry I know I could search for this info, but I figured you would know.

[trac209]

You can put a master gauge in under the hood to check the actual pressure without actually installing a gauge in dash. The temp gauge usually goes in the cyl head. I have a higher pressure switch hooked up to my idiot light that comes on at 18psi. So if you see the light go on there's something to investigate. Keeps the factory interior look.

[davepl]

I don't like the 30W idea, except for chainsaws. An engine in good condition should be able to idle down, fully hot, at 600rpm and not trip the light. I think the lights don't come on until 7psi. That's not a lot to keep your crank and rods 'floating'.

I've had worn engines that would flicker the light when hot at low rpm. But you'd like to see around 20psi I think.

Thicker oil can help but it is a bandaid that just delays the real fix (which is to pull the motor and sell it on craigslists as 'ran great when I pulled it').

[1972BlueC20]

I really doubt my engine is shot. It runs too good. I might stick with 10-40 and just try a better oil filter first. I'll also check the oil pressure. If all seems good. I'm going to keep going down the road.

[1972BlueC20]

UPDATE :

So I changed my oil and used a wix filter, and the oil pressure light is still pulsating on and off when stopped at idle in drive or reverse. Doesn't do it in park. So it wasn't the fram filter after all, but I still won't use fram anymore. Dude at the parts store showed me a fram versus wix side by side cut open...wow...that's all I can say.


I didn't get around to buying an oil pressure gauge yet. I might try to turn up my idle but I really think the idle is about right as is. I'm worried my oil pump is going bad. Are the oil pumps hard to replace? Any other suggestions???

[davepl]

Yeah, oil pumps aren't easy on Chevrolets. You could probably change it in the car by dropping the pan, but I've never done one in-vehicle.

I think you need to put a gauge on it. Guessing isn't getting us any closer, we need some data. Remember you don't need to mount it or anything, just hook it up back by the distributor (on a small block) temporarily so you can get some readings. Tape it to your wiper if you need to drive it for the test.