Hi. Just joined this site and love all the mopar posts. Having a problem with my rebuilt 360 and wondering if anyone has experianced this or has an idea whats happening. Block was hot tanked,new cam bearings,plugs,bronze bushing. Crank was polished and mic'ed at machine shop. New bearings installed with 002" rod and main clearance. M.P/ Melling hv oil pump, hardened tip shaft, 7qt pan. Everything was checked and triple checked,cleaned and recleaned as i always do. 450" hyd cam and lifters were new. Indys rebuilt Aerohead 360 heads with 2.02 valves for future cam upgrade. Engine started right up and ran great for 4000 miles. Changed oil after first 100 miles, then again at 500 and 1500. Running Valvoline 10w40 with Lucas zinc additive and mopar filter. Oil pressure is cold idle50psi. Hot idle is 30psi and goes right up to 65psi over 1500 rpm. Problem just started coming home from work. Hit the throttle, and oil pessure drops quick. Goes down the road and idles fine, and i can rev to 5500 in neutral and all is well. Put it in gear and it doesnt matter if i go wot or half throttle, the pressure drops and i let off pedal, returns to 65psi. Anyone have an experiance like this just happen all of a sudden? Getting worried as its my work vehicle at the moment. Seems fine under normalish, light driving conditions, but i like hearing those turbo mufflers and headers sing. I tried a different gauge for the heck of it, no change. Thanks for any info or input.
360 oiling problem under load
- Thread starter Dartish
- Start date
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The one time that I experienced a condition like this was on 390 Ford truck engine. But it had a lot of miles on it. I had installed a mechanical oil pressure and a mechanical water temp gauge in it. I noticed at an idle or when I reved the engine it had good oil pressure. But when I drove it under a load the oil pressure would drop when under a load and as soon as I let of the gas the oil pressure would jump right back up to 45 PSI. Turned out to be worn out Main bearings. Dropped the pan, put a set of new mains in it, problem solved. In your case you say the engine is new? I still think you have a bearing issue.
I bet there's a leak somewhere and the oil is low. Have you checked the oil level on the dipstick?
Do you have another gauge handy?
He did mention that he tried another gauge with the same results.
That is a good idea, especially since this is a new build.
I was thinking it seemed like a bearing issue, but keep wondering how it would have chewed up mains so quickly, especially since it seemed to happen all at once. And still has the same oil pressure it had when first started. Was hoping it was just relief valve in oil pump or something but ive never had one stick or had an engine go so quickly. 20yrs ago i was building circle track engines, several street/bracket engines and never had an oiling issue. Always used good parts, very careful about keeping everything clean and checking tolerances. Appreciate the input. Ever try running thicker oil in that old 390?
I figured the reason I was loosing OP , was because under a load the crank was being pushed down away from the block oil holes thus the OP dropping. And then the opposite when I was letting off the gas. Heavier weight oil once the engine is warm will not boost your pressure significantly. Had a 300 Ford 6 that I rebuilt many years ago that the Machine shop had turned the crank wrong and I wound up with way more main clearance than I should have. When I brought this fact up to them they told me " ah it will be all right" I knew better but put it together anyway. Sure enough 50 PSI cold, 0-5 PSI when hot. I was pissed, dropped the truck off to the Big A machine shop in Seffner Fl and told them , "I told you it wouldn't have oil pressure, now you fix it" They kept it a couple of days and when I came back i caught them putting 50 w racing oil in it! I told them go ahead, that it wouldn't fix it. Started it up, 60 PSI cold, they were all smiling. Till it warmed up, 5 PSI at a idle! They washed there hands with it and I never used them again!
Its getting pretty hard to find decent macine shops or even decent parts without spending your life savings. Seems u can spend decent money on name brand, matched components, and still do everything you know of right, and end up with half of it being junk. Makes the hobby alot less enjoyable then it was 20yrs ago. Makes me think a Prius might be in the future.haha
I remember another thread where a member was fighting with a oil pressure problem and in the end it turned out he didn't have enough oil in his engine! As RRR said in post #3, make sure your crank case is full. Start with the basics. I would then take your oil filter off and cut it open, check for medal in the filter.
MOPAROFFICIAL
Oogliboogli
It could be debris in the pump, had this happen and free rev'd it over 6k to clear it and get it home, still running 8 yrs later. More than likely if not the above..then low oil level, the mains don't necessarily have to be worn.
I checked oil the first time i saw the needle drop. Its full. Used less then half qt the first 500 miles. Hasnt burnt any since the rings got happy in their bores and no leaks. Probably cut the filter open after work. Luckily i only have to drive a few miles to work.
Was it losing pressure only under a load or in neautral too?
Only under load, it was fine at idle, when cruising or when free revved. Under load of about 1/3 throttle or more the oil pressure would drop right off. Let up and it cam right back. It happened about 2000 miles after a rebuild on a 340. No engine or bearing damage occurred before I fixed it and it was about 300 miles from home when it started.
Sounds exactly like what im experiancing! Be nice to drop the pan and find a pick up tubes all it is. Thanks for the input. Was the crackvisible while it was still screwed in the pump?
It wasn't visible until removed but it was there. It doesn't take much. I tore the whole engine down to inspect it for damage and found nothing. A simple pickup replacement and oil change would have been much easier. When I cut the oil filter open it was clean too.
I have seen this problem 3 times on other cars in the 20 years since I had it happen and no engine damage occurred to them either.
That would be good news in the grand scheme of things.
Im gonna cut open the filter at work tomorrow and maybe drop the pan and pump. Was hoping this motor would live. Ordered the heads with the 2.02 int valves because i was planning on swapping to a more aggressive cam and a tall dual plane intake in the spring.
Keep the faith, maybe it will work out good for you.
famous bob
mopar misfit
oil filter collapsing under load ?
nm9stheham
Well-Known Member
An oil filter would normally collapse in neutral and not moving, just as much as moving with engine under load. I would be looking at the pickup system as suggested: either in the tube or the pickup head or something in the pan moving under acceleration.
OP, also measure the quantity of oil that you drain very carefully. Your dipstick markings could be off and misleading you; there are several dipsticks out there for different pans and engines. Also, if the pickup is too high above the pan, it could becoming exposed to air if you burned up some oil since your last change.... which sounds like it was 2500 miles ago from your info, so you could have burned some off and have lower oil than when you last filled it. In fact, before pulling the pan, I would add half or 3/4 of a quart first and see if that fixed things.....that would tell that part of the story.
OP, also measure the quantity of oil that you drain very carefully. Your dipstick markings could be off and misleading you; there are several dipsticks out there for different pans and engines. Also, if the pickup is too high above the pan, it could becoming exposed to air if you burned up some oil since your last change.... which sounds like it was 2500 miles ago from your info, so you could have burned some off and have lower oil than when you last filled it. In fact, before pulling the pan, I would add half or 3/4 of a quart first and see if that fixed things.....that would tell that part of the story.
MOPAROFFICIAL
Oogliboogli
Funny, I've had the pick up tube swinging back and forth, loose in the threads, and never lost oil psi as the op and TNT says.
I'll bet it is debris that was left in the oil pasages, improper cleaning before assembly. Honestly I have never heard of or had a cracked pick up tube, let alone would I ever miss something like that during inspection and assembly.
Dirt in the pump spring, anything over 2800-3000 and the psi will drop into the teens.
Best of luck finding, but make sure you really find the cause...That way people can learn something here.
I'll bet it is debris that was left in the oil pasages, improper cleaning before assembly. Honestly I have never heard of or had a cracked pick up tube, let alone would I ever miss something like that during inspection and assembly.
Dirt in the pump spring, anything over 2800-3000 and the psi will drop into the teens.
Best of luck finding, but make sure you really find the cause...That way people can learn something here.
How do you know your problem was caused by the debris in the pump? Did you find it, use your crystal ball or was it just determined using SWAG. (Scientific Wild Assed Guess) I would guess the latter.... if so you you really needed to find the cause...That way people can learn something here, not just follow your assumptions and guesses.
If dirt in pickup spring anything over 2800-3000 and the psi will drop into the teens I would have seen that since my car cruised at 3700rpm for over 200 miles on the return trip. I could cruise at 4000+rpm and hold 65psi constantly also. The crack wasn't visible because it was right by the pump on the top side. I found it because the pickup was actually moving/flexing as soon as I felt the pickup. The leak was much larger then what a loose pickup could ever cause. I've seen loose pickups many times and they weren't ever an issue.
This is a common problem in some engines, 7.3 diesels are known for having these issues and symptoms. A cracked oil pickup is the cause.
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