Jump to content

Flash of Oil Pressure Idiot Light


freddiefokker

Recommended Posts

Greetings. I'm getting an occasional intermittent flash of my oil pressure warning light in my all stock '71 402. It flashes sometimes while idling at a stop light or stop sign, always while in drive, never in Park.

I hooked a manual oil pressure gauge up to it in the shop; plenty of oil pressure at idle in park and in gear. Oil looks and smells good with no gas smell. Changed the oil (Valvoline Racing 10w-30). Turned the idle screw up a turn. Idles at 700 in Park and about the same in gear on a Sun tach. Replaced the original oil pressure sending unit. No change.

It's a real low miles (23k) all original engine, so it's sat a lot, but has always been started and run regularly throughout it's easy life.

I'm fairly confident it's an indication thing; like I said, It's got plenty of oil pressure on a manual gauge in the shop. My motor guy says use 20w-50 oil...

Any ideas?

Link to comment
Share on other sites

when you took your oil pressure reading did you take it from the same point as the sending unit. I would check at that point and I would warm the car up and drive it to simulate the condition. If you still feel you have hood oil pressure then check the voltage and possibly it has some resistance somewhere. 

Link to comment
Share on other sites

Yes, I took the reading from the sending unit port by the oil filter. Warmed up and on a lift. 20-22 psi at idle, a little more reving it just a bit on the lift. It only does it in Drive at or approaching a stop. I don't think it's an engine problem but it's got me a little curious.

Link to comment
Share on other sites

2 hours ago, MC1of80 said:

Change the oil pressure switch. Very common issue with old GM cars and trucks. And also raise the idle slightly. 

Thanks. I had already changed the sending unit. No change. I turned the idle screw up a turn. Same thing. 

Link to comment
Share on other sites

I would have to agree with thicker oil. My 72 had 10/30 in it and sounded like a typerighter and oil light would come on when hot . Put 10/40 oil and sounds like a different engine and no light.good luck

Link to comment
Share on other sites

I'm going to agree with IMR's/Antoine post its a resistance thing. If its an "idiot lite" then its electrical from the sending unit to the IP. You would have to trouble shoot the harness and all connections.  My suggestion is not for the purist/all factory oem crowd, since oil pressure is a pretty important thing you could mount a small mechanical gauge somewhere and be done with it. They are pretty inexpensive and I would definitely not use the plastic line supplied with most kits. (auto meter part # 3224 would be my recommendation) 

Link to comment
Share on other sites

Reason behind electrical is you say you have 20lbs of oil pressure. that is plenty to keep the light off. You mentioned that you already replaced the sending unit and I will believe it is not defective. I will also agree with DragCat do not use a plastic line. I know from experience it is a disaster waiting to happen.

Link to comment
Share on other sites

I have idiot lights on my dash also ,I installed additional sw gauges under the dash ,oil pressure ,coolant temp, and voltage meter, i want to know what is going on with my car all the time , so if the gauges start to climb i can turn the car off. 

Link to comment
Share on other sites

Ok, I installed a cheapo set of Equis guages and I still have the same problem. At every third or fourth stop sign/light, the oil pressure drops below approx 12, the idiot light comes on, it drops on the guage to below 10 and then recovers. It seems to recover faster when I let off the brake. Vacuum? I'm perplexed, dudes.

So far, I've changed the idiot light sending unit, changed the oil from 10w30 to 20w50, turned up the idle a turn, and installed a manual op guage.

The car has plenty of op at idle (20) and 30-40 going down the road.

Any ideas?

Link to comment
Share on other sites

I would definitely start by looking for a vacuum leak/issue. Did you T the idiot light or run direct line from the block to the gauge? Vacuum issues will drive you crazy no doubt.

Link to comment
Share on other sites

Are you using regular or synthetic oil.  Since the gauge and the light seem to agree.  Since it is low mileage I would think it is not bad crank or cam bearings unless someone had opened the engine for something and changed something.  I guess it could possibly be an oil pump issue.

rob

Link to comment
Share on other sites

1 hour ago, DragCat said:

I would definitely start by looking for a vacuum leak/issue. Did you T the idiot light or run direct line from the block to the gauge? Vacuum issues will drive you crazy no doubt.

I put a tee in the block so I could keep the stock warning light and plumb in the manual guage.

Link to comment
Share on other sites

Is your oil pan original. I had a vehicle do this once and removed the oil pan to check for trash in the pan and found they had an aftermarket oil pan with no baffle. the oil sloshing around made the light go on when braking, accelerating and turns. I dont know, why its low when braking. usually cam bearings are the first thing to give you low oil pressure. maybe bad pressure relief valve in the oil pump. Is this a new problem.

Link to comment
Share on other sites

On 4/12/2019 at 8:58 PM, freddiefokker said:

I think it's a bad oil pump relief valve.

Sometimes it's the simple solution. My motor guy called me and said, "Before we start messing with dropping pans and looking at oil pumps, add a quart of oil."

Well, that fixed it. I know the 402 is supposed to take 5 qts, but when I was a kid, my Dad had two 454 trucks on the farm and they both took 6 qts. My car was just a little below the fill line with 5 qts and now it's a little over the line with 6. No flashing oil light and no drop in oil pressure at stop lights now.

So I guess the new sending unit and change to 20w50 was a waste of time. Who knows. Next oil change she gets 5.5-6 qts.

Link to comment
Share on other sites

I had a problem years ago with oil pressure dropping when coming to a stop. But would come back up after I had stopped. I was told to drain the oil and after the pan was empty to bang on the bottom of the pan with my fist. When I did this I could her something some thing bouncing on the bottom of the oil pan. Turns out my  oil pump  pick up tube had come off. What was happening was when coming to a stop the oil would move forward away from the oil pump and with the pick up off  the pressure would drop off for a moment. Just seems to me that being a quart low  should not cause loss of oil pressure. 

Link to comment
Share on other sites

I'm glad you fixed the problem!

I don't think the oil filter was mentioned. Always use a quality filter, Wix, Hastings, Mobil 1, K&N. Fram, cheap and store brands, and even some ACDelco filters are pretty poor. And always use the longer truck filter.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...