Hello everyone...this is my first post so I thought I'd say hi first.

okay...I just changed the oil in my 1980 z28 350 auto. At first the oil pressure light was off. After I drove it around for a while, it would come on at 55-60 mph (2500 rpm) and then turn off when I'd let off the gas. Now it stays on all the time! What the heck? Here's some factors you should know...

-I've had the car for 10 years and the light has NEVER come on until now
-I added 1 quart of Lucas oil to 4 quarts 10w 30 and Fram filter
-The car is still running great.
-Plastic (not the wires) on the oil pressure sending unit connector is cracked, but it stays in place well
-there is oil in the NEW crankcase filter by the air cleaner
-I let about 1/2 quart out and the light's still on
-Last time I changed it before this was a year ago (I don't drive it much and I had added lucas oil before...the oil was still pretty clean when I changed it...less than 1000 miles put on it in a year)
-I was gunning it quite a bit after it warmed up after i changed the oil
-I added the lucas oil first and it was cold when I put it in
-there is old gas in the tank...when it gets to the bottom it starts running like crap

so, what do you all think?

oh yeah, does anyone know an easy way to get the oil pressure sending unit out...it's really hard to fit a wrench there.

my dad is telling me to put Kerosene in it and let it run for a while, then change the oil and don't put Lucas oil in it...that sounds weird though

does anyone have any ideas? I really love this car and I can't afford an overhaul right now--I'm pretty worried...It's been with me since I was 15

thanks for your help everyone
white05gt

There is a oil sender socket made for this purpose of changing out the sending unit. It really works. I would change the sending unit before doing anything else, then drain the gas tank and add new gas.

Dad's suggestion of adding kerosene to the crankcase is for the purpose of cleaning the sludge from the crankcase/block. Then drain it and add new oil. Not a a bad idea, did it to a couple of tractors on the farm and they still ran find. Dads don't give out bad advice.

Change the Fram filter to an AC/Delco filter, there is a difference.

With the light coming on at highway speed may be an indication of poor drainback of oil from the top of the engine. Sludge and valve stem seals may be plugging the drain holes at each end of the heads. Seals get brittle/dry rot from age and collect in the drain holes.

Welcome to the club.

yeah my Dad's pretty smart...most of the time. :D He's a mechanical engineer. sounds like you must be a dad too.

Wow, a socket made specifically for that! Should've thought of that...thanks!

oh yeah, we had a valve job done (replaced the seals) on the car and we honed the cylinders/put new rings on about 20,000 (6 years) ago, so I figured it wouldn't be doing anything yet...

Yep it may not be draining back down well because I checked the level shortly after I drove it the first time and it was 1/2 quart low...then I checked it after a few days (warm) and it was full...

alright, thank you so much for your advice, sir, and I'll mess with it this weekend and get back to y'all later.

white05gt

I would temporarily install a cheap mechanical gauge to be sure your sending unit or wiring isn't going bad. I don't think clogged oil return passages are keeping your oil from getting down to the oil pump pickup, because I've seen really clogged up engines that still had good oil pressure. Is it possible you damaged the bottom of the oil pan or bent it in a little? You didn't lift the engine with a floor jack on the bottom of the oil pan, did you? Your oil pump pickup sets very close to the floor of the pan and if you damaged the pan, it could hamper oil from being sucked up by the pump. I'd inspect the bottom of your pan and install the temporary gauge (around $10 @ the local autoparts store) to verify you actually have low oil pressure. For what's it's worth, my factory gauge on my F150 reads at the low range, but has 60 psi at idle (verified with a gauge). Let us know, Tom

Patrick ,
From Your Post Is Seems You Only Had The Problem After Changing Your Oil . Change It Again With A Different Brand Of Oil Filter . I'm In The Auto Parts Business And Defective Oil Filters Are Not Uncommon As They Are Mass Produced . You Can Get An A/C Delco Filter For The Same Price .
Good Luck
Ben

to verify you actually have low oil pressure. For what's it's worth, my factory gauge on my F150 reads at the low range, but has 60 psi at idle (verified with a gauge). Let us know, Tom




FYI Tom, on Fords the oil pressure gauge is on the same sender as the idiot light and the sender isn't scaling. It is either open or closed. Therefore it is an idiot gauge. I discovered this on a 2000 F-350 that the gauge started dropping in the middle of nowhere. I teed in a digital manometer(0 to 150 PSID range) with 1/16th tubing and ran like this about a week with the idiot light off and gauge dead while I waited for Ford to get a new sender. That didn't fix the gauge and I asked my buddies at Ford WTF? They said yeah the gauge is shot, but it's not really a gauge cuz Ford got sick of people complaining about oil pressure problems about 20 years previous. So I put a mechanical gauge in it. And since then I've noted how Ford oil pressure gauges are rock steady like you would never expect on a real gauge.

Tim, Thanks for the info. Obviously, not one Ford's "better" ideas, lol. I'm curious to see what the problem ended up being for white05GT's low oil pressure.

hello everyone,

I think I figured out the problem this weekend...

First thing I did was replace the oil pressure sending unit, since it's cheaper that 5 quarts of oil. The light was staying on and everything before I replaced it.

After I put on the new one, guess what...the light wouldn't come on AT ALL! not even with the ignition on and the car not running...so I assumed the bulb had maybe burned out. So I took the instrument cluster out to check the bulb (various 30-year-old pieces of plastic breaking everywhere!!) and guess what...the bulb was fine, and when I put it back together, the light is now on all the time again!!!

so now I'm thinking the connector or the wire somewhere between the switch and the light is bad...

Also, why would the light change in brightness when the engine rpms get higher? When I first started the car, it was idling real slow (choak not closed all the way) and the light was dim. I raised the rpms just a little and the light got significantly brighter!!??

taking my chances in a slight fit of rage after breaking pieces of my instrument cluster...I drove the car around for 20 minutes to see if any tapping would start happening...nothing happened...it runs really nice...lots of power.

I really think it's just an electrical problem. I don't have the money this week to get a gauge, but I've decided I really need one...not sure where I'll mount it though...

It still seems strange, though, that it started right after I changed the oil.

okay y'all, I'm gonna change the connector and put an ac delco filter in next weekend and then get back to you.

thanks so much to everyone

TO BE CONTINUED...

hey Tom,
I raised the car on the frame...
I'll get an AC Delco filter for next weekend...but I'm pretty sure the connector or the wire is the problem...check out my full post and you'll see what happened.
thanks for you're advice, my friend

hello everyone,

I think I figured out the problem this weekend...

First thing I did was replace the oil pressure sending unit, since it's cheaper that 5 quarts of oil. The light was staying on and everything before I replaced it.

After I put on the new one, guess what...the light wouldn't come on AT ALL! not even with the ignition on and the car not running...so I assumed the bulb had maybe burned out. So I took the instrument cluster out to check the bulb (various 30-year-old pieces of plastic breaking everywhere!!) and guess what...the bulb was fine, and when I put it back together, the light is now on all the time again!!!

so now I'm thinking the connector or the wire somewhere between the switch and the light is bad...

Also, why would the light change in brightness when the engine rpms get higher? When I first started the car, it was idling real slow (choak not closed all the way) and the light was dim. I raised the rpms just a little and the light got significantly brighter!!??

taking my chances in a slight fit of rage after breaking pieces of my instrument cluster...I drove the car around for 20 minutes to see if any tapping would start happening...nothing happened...it runs really nice...lots of power.

I really think it's just an electrical problem. I don't have the money this week to get a gauge, but I've decided I really need one...not sure where I'll mount it though...

It still seems strange, though, that it started right after I changed the oil.

okay y'all, I'm gonna change the connector and put an ac delco filter in next weekend and then get back to you.

thanks so much to everyone

TO BE CONTINUED...

If you are suspect that the light and wire are bad, just run a new wire, bulb and socket from the engine bay into the car via the window. Check a wiring diagram, but I think senders work by grounding to the engine block so all you have to do is plug one side of the bulb into a hot lead and then connect the other side to the sender.

Quick and dirty

alan