Oil pressure light coming on at idle

-
M

Mrpatatomoto

Active Member
Joined
Mar 30, 2011
Messages
30
Reaction score
0
Location
Escondido, CA
On our 65 Valiant we switched to Electronic ignition aboiut a month and a half ago and tuned it down to stock idle specs and since then when the car is at idle the oil light comes on but if I give it any slight bit of throttle the light goes off. I just figured at the low idle we have it at its not getting pressure to the switch and have been driving it with no problems. But my dad got in it today and is saying I shouldn't drive it till I find out the actual reason its coming on. What do you all think? The oil is kind of thin and needs replaced but from my knowledge that doesn't change pressure. My best guess is just turn the idle up a little and it will be fixed, just figured id ask and see if it could be a bigger problem than that.
 
It takes only 9 lbs of oil pressure to turn that warning lamp off.
Once the engine gets hot much of the oil pressure is lost through the main and cam bearings so the top end where the sender is isn't getting more than 9 lbs. at idle rpm. To drop the pan and replace the oil pump and screen might cure it for a long time.
I guess the first thing to do is install a true oil gauge and see the actual pressure variance from cold to hot.
 
RedFish said:
It takes only 9 lbs of oil pressure to turn that warning lamp off.
Once the engine gets hot much of the oil pressure is lost through the main and cam bearings so the top end where the sender is isn't getting more than 9 lbs. at idle rpm. To drop the pan and replace the oil pump and screen might cure it for a long time.
I guess the first thing to do is install a true oil gauge and see the actual pressure variance from cold to hot.
Click to expand...

the sending unit is right on the oil pump next to the oil filter on a slant...

but yea install a mechanical gauge on a T fitting so the light will still work...
 
My Nissan (I know it's not a Mopar) did the same thing. Turns out the oil pan got squashed in a bit and was sitting right on the pick-up tube screen. Knocked the oil pan back out and the problem was gone.
Rod
 
rklein383 said:
My Nissan (I know it's not a Mopar) did the same thing. Turns out the oil pan got squashed in a bit and was sitting right on the pick-up tube screen. Knocked the oil pan back out and the problem was gone.
Rod
Click to expand...

mopar pickup's have a notch cut in them so they sit on the floor of the pan but always allow flow...

nobody asked how many miles...
 
Yet another example of Mopar's better engineering!

805moparkid said:
mopar pickup's have a notch cut in them so they sit on the floor of the pan but always allow flow...

nobody asked how many miles...
Click to expand...
 
Some of the senders are a little more alarmist than others and will tend to trigger the light at the low end of normal oil pressure, especially with hot (thin) oil and slow idle in gear. Take note that when the oil pressure sender diaphragm starts to leak, you get unwarranted oil light illumination and a tough-to-find oil leak. The proper thing to do would be to put a mechanical oil pressure gauge on the engine and check to make sure you've got adequate oil pressure, but if you haven't got one readily to hand, it may not be worth your hassle to mess with a mechanical gauge. I would put a new sender on it. It will also be a good idea to service the oil pressure relief valve to make sure it's not stuck partway open and is doing its job, as described in these two threads: thread 1, thread 2.

Also, what type of engine oil are you using?
 
slantsixdan said:
Also, what type of engine oil are you using?
Click to expand...

We've only had the car for about 4 months not driving every day but not sitting and the PO said he did an oil change a month or so before selling it to us, so idk what kind/weight of oil is in it now but we need to change it soon. Ill get the mileage tomorrow got busier than expected tonight so never had time to fiddle with the car.

And thanks for the links, I searched low oil pressure but didn't come up with anything that answered my problem in the first page. Probably wont be able to get a mechanical gauge tomorrow being a holiday but maybe Tuesday. Hell, I've got one sitting in my TR7 that's not finished yet so if I really needed to I could take it out of that, but it would never go back so I don't really want to do that...

Thanks for all the suggestions.
 
The oil is kind of thin and needs replaced but from my knowledge that doesn't change pressure.
Click to expand...
The Viscosity of the oil definitly has an effect on pressure. I'm running 10W30 in mine. A temp. fix is to use a higher viscosity oil. I ran 20W50 until my new oil pump showed up. Some motor oil additives also increase viscosity. To me this was just a temp. fix. Also do some research on the oil pump drive gear before changing an oil pump out. The main thing is to check it with a gauge.
 
First off, per the 1966 Owners Manual this is a "normal" condition. But its certainly not optimal. Pull the valve cover. Is the engine a sludge monster? This will tell you a lot about how a slant was cared for. It could be that the oil pressure switch is sludged up and idle pressure won't turn the lamp off. A bit of crud may have the bypass stuck part way open too. Actually pretty common on grandma driven slants. Clean the bypass, replace the switch and run 15w40 Rotella. Also run the engine with the valve cover removed. Make sure everything is getting oiled. I've seen slants where the rocker arms and shaft were so clogged up that the rockers actually squeaked.
 
Since we are getting into oils. What advice for oil weight in a good running non noisy slant. I've only recently got it and changed oil immediately. I used 20w50. Good choice or no?
Thanks
 
Actually, I'd like to clarify and amend my oil recommendation. In a new, or low mileage slant (or any other stock Mopar engine of the era) 10w30 should be fine. 15w40 is slightly heavier and may increase the indicated oil pressure (measured at pump outlet), but this will be at the potential risk of decreased circulation, especially during cold operation. 20w50 is thicker yet. Remember that viscosity is defined as the resistance to flow.

So why did I suggest 15w40? I made the assumption that you had a high mileage engine, possibly with a sludge issue. Being a diesel engine spec oil, it will have a more aggressive detergent package, and be more able to suspend contaminants helping to clean your engine over time. (I don't buy into the zinc ballyhoo, but diesel spec oils tend to contain more zinc than gas spec oils, although not as much as they once did). When I was still driving my 65 daily, I ran 15w40, but it has well over 200k on the original engine. And yes, on a hot day my oil lamp will flicker at idle.

As an aside, I have began running 5w40 synthetic in most of my engines (Mobil 1 TDT). My VW TDI requires it, my 4.0L Jeep loves it, and I don't have to keep a bunch of spare quarts of different oils around.
 
C130 Chief said:
I have began running 5w40 synthetic in most of my engines (Mobil 1 TDT). My VW TDI requires it, my 4.0L Jeep loves it, and I don't have to keep a bunch of spare quarts of different oils around.
Click to expand...

Yup, a good brand of 5w40 synth is a very good pick for most any engine (new or old) in sound mechanical condition.
 
Like others have stated.....check to see if the oil pressure is actually low or if it's just a faulty sending unit. If the oil is thin, change it and the filter. I suspect that the engine just has a lot of miles on it and needs new bearings. Heavier weigh oil will get you down the road a little while longer but it's no cure for bad bearings. As for viscosity ratings, a lot will depend on your climate and the use for which you put the engine. When it's 40 below, 0-20W might be too thick on a new engine.....when it's 110 in the shade, 20-50 is fine on an engine with some miles on it.
 
Oil threads are becoming fun.
Try this out: any oil with multiple visc, has 1/3 of additives in it, that are not oil. Use straight 30 or 40.
 
Dan's gonna HATE this one.:D

In and old high miliage motor that may be gunked up you can run 50/50 of 50wt oil and transmission fluid to clean up some sludge that might be blocking the oil from rockers and even oil pump regulator valves.
Run it for a day or two, then change it (Filter change is a MUST)
I works about 50% of the time due to the heavy detergents in the trans fluid.
If you have high miles and low oil pressure and there is nothing you can do about it, then a can of STP oil treatment will shut your light off.

All the above is only temporary of course, but I have run cars for years after doing it.
 
That or run a can of motor flush. Put it in at the parts store and drive home on it. do an oil and filter change immediatly while its still hot. Just buy it close to home, like 3 miles max. If you really want some fun, do a seafoam treatment wne you get home too. put 1/3 in tank and suck rest of bottle into intake manifold via vacuum line, turn off motor and eat some lunch. Come back out, start up and watch the smoke show! When smoke dies down, change oil and filter. Itll make smoke that will block out the sun....remember the space shuttle launches? hilarious!
 
If you take the bulb out of the dash, the light won't come on anymore....
 
In my experience the oil light at idle is the beginning of the end. Had a 198 start doing that after the Po had "extended" the oil change intervals out to about every 12000 miles...

New pump turned the light back off at idle but didn't save the engine later on...knock knock knock.
 
You must log in or register to reply here.
-

Back
Top