engine loses oil pressure when it hits 200 degrees

[amxer]

I have a new rebuilt motor 69/390 bored 60 over, balanced, ported 58cc heads, comp cams 280h, push rods, lifters and springs with scorpian rollers.
Everything is new in the motor except for the crank, and the timing chain cover. I replaced the oil pump gears, checked the walls of the pump and they seem to be fine. I am considering replacing the timing chain cover to see if that will make a difference. But if any of you have experienced this problem, please let me know. I would hate to have to tear this engine down.

Car runs fine down the road but once it gets a little warm the motor loses oil pressure. Also there is no knock or lifter noice when pressure drops off. And the oil pressure is at 0 at an idle in gear, and goes to 20 when you have it in park. I also changed oil pressure gauges. :confused:

[304_dude]

Hi, it sounds like the filter bypass valve is stuck open... When your engine oil warms up to operating temp, the viscosity drops to 10w thus oil pressure loss.

Since you have a fresh rebuild... did the engine dude use non-detergent 30w for break-in? 1,000 miles of variable cruising speeds... today's hustle and bustle drivers get annoyed easy by it.

If your still running it passed break in period you can have viscocity breakdown also... since they do not make off the shelve straight 30w without additives anymore.

I learned to kill the bypass valve along time ago as a race trick. It is realitivly simple and not recomended for those who are not changing their oil filter with every oil change.

[amxer]

I will check the oil bypass out this weekend dude thx for the tip. The motor has only been run for like 35 miles or so. I used crappy 30 weight oil when breaking in the cam , which according to comp cams is 2000-2500 rpms for a half an hour. Then I changed the oil and filter. Used straight castrol 30 weight. I will let ya all know what's happening with my progress. :)

[Gremil]

Hi, it sounds like the filter bypass valve is stuck open... When your engine oil warms up to operating temp, the viscosity drops to 10w thus oil pressure loss.

FYI - The 10W-30 means that at 210 degrees F or at 100 degrees C the viscosity is SAE 30. The "W" is taken at a colder temperature on a scale used depending on which viscosity being tested. It measures how much a Motor Oil thickens when it drops in temperature for cold starting purposes.

The "W" has nothing to do with anything after a motor has warmed up. It is measured at cold temps, say 20 degrees F for example.

The SAE 30 and 10W-30 oils are the same viscosity at 210 degrees F. The difference between a straight weight pertroleum based motor oil and a 10W-30 is that if the straight weight were tested at colder temperatures it would be called a 30W-30.

If you do away with the by-pass valve in your system you may need to read this. Even a stock motor at idle by-passes some oil from time to time to prevent oil pressure loss. If you do have a problem with the by-pass valve it would be better to fix it if at all possible. If you do remove it, better use a high end oil filter that comes with a built in by-pass valve to be sure to get full oil flow. Just a thought. :)

A local guy with a potent AMX Drag Car had a oil pressure loss and just changed the oil filter and the pressure came back. It was a new engine which may mean that debris collected in the filter and clogged it. I don't know if you tried that yet. ;)

[ChevelleSSLS6]

FYI -
A local guy with a potent AMX Drag Car had a oil pressure loss and just changed the oil filter and the pressure came back. It was a new engine which may mean that debris collected in the filter and clogged it. I don't know if you tried that yet. ;)


switching to a new oil filter (i went from a fram wich had 0psi at anywhere to a wix with very good pressure even at idle) worked for me too, 74 jav 360, only mods are removed air pump and a holley 600.

[donsjave]

I have a new rebuilt motor 69/390 bored 60 over, balanced, ported 58cc heads, comp cams 280h, push rods, lifters and springs with scorpian rollers.
Everything is new in the motor except for the crank, and the timing chain cover. I replaced the oil pump gears, checked the walls of the pump and they seem to be fine. I am considering replacing the timing chain cover to see if that will make a difference. But if any of you have experienced this problem, please let me know. I would hate to have to tear this engine down.

Car runs fine down the road but once it gets a little warm the motor loses oil pressure. Also there is no knock or lifter noice when pressure drops off. And the oil pressure is at 0 at an idle in gear, and goes to 20 when you have it in park. I also changed oil pressure gauges. :confused:
You also might want to think about the bore on the engine. I have been told by some AMC builders that you do not want to go over the 40 over mark on the engine bores. Anything much over that will make the engine run too hot and the 60 over on the boring will run the pistons too close to the water jackets. Just a thought

[Spider]

I too am having the same problem and I flushed the motor with kreen first. Then I dropped the pan to look at the pick-up to see if it was blocked. It was clogged with a bunch of old gasket material, the jerk who owned the car before me was lazy. Next I rebuilt the oil pump and replaced the oil pressure gauge. I too am using a fram oil filter. My oil pressure seems to drop severly after the car has warmed up after about 15min. Could my problem be the relief valve or the filter? If it is the relief valve where is this located so I can check it out or disable it? If it is the filter what filter do you recommend or where can I get a wix filter. Thanks

[donsjave]

Just a thought here, my 360 kind of went thru the same stuff with the oil pressure drop off when the engine got warm (operating tempature). It ended up being the clearances for the bearings and rods were set at GM specifications and this screwed up everything in the lower part of the motor. This was due to the machine shop not knowing that AMC specs are very tight down on the crank and the such. Like a dummy, I did not check to make sure that everything was correct. Different story with the 401 that went back into the car. Not wanting to scare anyone here, I would check your clearances and see if they were set by the machine shop to GM specs. A lot of shops do not have the specs for AMC's anymore and instead of asking the customer if they have them, they will use the GM specs so they won't look stupid or something. :eek:

[Calpwr]

Just one thing on your engine, make sure you are breaking the engine in with non-detergent oil, if you don't you will run the risk of the rings not seating and oil consumption problems down the road. I agree with the post on the by-pass valve that is the first thing I would look at.


I have a new rebuilt motor 69/390 bored 60 over, balanced, ported 58cc heads, comp cams 280h, push rods, lifters and springs with scorpian rollers.
Everything is new in the motor except for the crank, and the timing chain cover. I replaced the oil pump gears, checked the walls of the pump and they seem to be fine. I am considering replacing the timing chain cover to see if that will make a difference. But if any of you have experienced this problem, please let me know. I would hate to have to tear this engine down.

Car runs fine down the road but once it gets a little warm the motor loses oil pressure. Also there is no knock or lifter noice when pressure drops off. And the oil pressure is at 0 at an idle in gear, and goes to 20 when you have it in park. I also changed oil pressure gauges. :confused:

[Hot-AMX]

I own a 68 AMX with a mildly modified 390, and noticed the exact same thing about the drop in pressure. When the oil is cool, I get about 20 psi on the gauge. Once the car warms up, the gauge reads about 12 psi. From what I have read, 10 psi is about the norm for gen 2 AMC V-8 engines. Yes, I thoroughly cleaned the screen - no debris, and replaced the oil pump gears. What did you ever figure out. How did you increase the oil pressure? I'm curious.
Thanks

[Big Bad AMX]

There's a thread regarding the internal oil line modification here (http://www.amx-perience.com/AmericanMotorsForum/showthread.php?t=790) that some of you may find of interest. I posted my reply there but because of the similarities of the topics in these threads I thought it may be helpful to get another perspective. So I asked Larry Mitchell, the former National Director of AMC World Clubs (retired) and owner of AMX Enterprises www.amx-enterprises.com (http://www.amx-enterprises.com/) for his opinion. He has built numerous AMC engines, raced his '69 AMX in many events over decades including the Silver State Challenge and the Pikes Peak Hill Climb. He replied with the following:

An ideal AMC V-8 should hold 20-25 pounds of pressure at hot idle and 60-65 pounds above 3,500 rpms. Please note that when these engines were new in the 1960s/1970s THEY DID! This is on 10W30 oil.

Rumors have abound for years about "oiling problems" inherent in an AMC V-8. IT ISN"T TRUE. AMC offered a 5 year, 50,000 mile warranty from 1968 and up and this is a period of time when owners of these cars were bashing them at stoplight drags on every street in America everyday and night of the week. And on weekends, they bashed their AMXs, Javelins, Machines, Scramblers et al at the dragstrips just like everyone else was doing with their Camaros, Cudas, Mach 1s, Challengers, GTOs and the like. AMC engines had no more or less problems with oiling than any of these other brand cars at the time. The only time oiling became a serious problem with ANY of the musclecars of 35 years ago was in SUSTAINED HIGH RPM DRIVING. Like over 100 miles an hour for 2 or more miles at a time. Then, any Ford, Chevy, Mopar or AMC engine would pump the pan dry and before the oil could get back into the pan, the rod bearings starved for oil and the engine seized and broke rods and stuff. Cornering back then on Polyglas belted tires and only a front sway bar caused no problems with loss of oil pressure because the average musclecar back then could not generate enough "Gs" to starve the oil pickup. With modern high performance tires of today and an aftermarket sway bar pack, you CAN easily starve the oil pickup on any of the old musclecars and trash the motor in seconds.

Overall, keep in mind all the Los Angeles AMC Police Matadors and the Alabama Highway Patrol 1972 Police Javelins had no special mods to the 401 motors with the exception of a slightly modified "police" oil pan. If all AMC V-8s suffered SERIOUS OILING PROBLEMS back then, don't you think they would have FIXED THE PROBLEMS to stop major financial losses on warranty claims AND don't you think the word on the streets and in car magazines back then would have killed sales of AMXs, Javelins and the like because engines would have failed right and left AND EVERYBODY WOULD HAVE KNOWN IT!?

A. If you are not going to drive your AMX or Javelin hard, you only need to make sure the following is done with an engine rebuild: The rod and main bearings MUST be clearanced as close to .001-inch as possible but not less than that figure. The rear main should be .0015. This is what all AMC shop manuals state the clearances are. If bearings are clearanced to "Chevrolet 350 specs" as most shops want to do, the oil pressure in your AMC V-8 will drop like a rock. Chevy engines oil the rods and mains FIRST and in order to pass lots of oil on to the rest of the engine, bearings are clearanced to .0035 to .0045-inch. AMC engines oil the rods and mains LAST and so bearing clearances must be tighter to properly lube and keep general engine oil pressure UP. Also in rebuilding your AMC engine, replace the timing cover with a brand new one, replace the oil pump gears with a new set, do not over tighten the oil pump cover-use stock torque specs and replace the oil pickup tube in the oil pan. This is all you need to do on a stock-to-strong street motor.
(note: the oil pickup tube can easily be cracked if overtightened and will suck air causing the oil pressure to drop. This can be very difficult to detect if you're not aware of it. ed)

B. If you put on modern high performance tires and especially an aftermarket sway bar package AND you "get on the car" some, run one quart over stock in the oil pan at all times.

C. If you are going to set up your AMX or Javelin today with serious modern high performance tires and a sway bar package and run the car damn hard a good part of the time, you will HAVE to have a "Trans-AM" style 8.5 quart "racing" oil pan with external pickup lines and oil pump bypass adapter.

D. If you are going to seriously race your AMC car in autcrossing or high-speed road or track events WITH SUSTAINED HIGH RPM DRIVING (above 4,000 rpm for more than 3 minutes), you will need the internal oil line from the front of the oil galley to the rear between #7 and #8 lifters. If you are NOT running SUSTAINED, HIGH RPM DRIVING/RACING, you DO NOT NEED THIS LINE! It is overkill and will drop your total engine oil pressure 5 or more pounds across the board.

Are you only getting 10-25 pounds above 3,000 rpms? If so, you have a serious DEFECT in your engine. Or, a faulty gauge. You can only really trust a mechanical gauge properly hooked up where the previous factory electrical pressure sending unit was. And, the gauge must have the line from the motor properly bled to get an accurate reading.

The biggest cause of low oil pressure is an IMPROPER REBUILD by a shop full of Chevy lovers!




.

[RacerAMX]

Who about the Pan to Pickup clearance? I rebuilt a 360 that had good pressure when pump was driven with drill, would loose pressure when engine started, Found out the pickup was too close to pan.

[Javelin360]

Holy cow am I glad I visited this evening. I stripped my 360 down to a long block state and will be dropping it off for rebuild at Nevada Valve Train tomorrow. I plan on having a talk with them about proper clearances and I copied all the specs from my service manual for them to go by.

My Specs indicate

Main Bearing Clearance .001 - .003 (.0025 prefered)

Rear main .001 - .003 (.003 prefered)

Connecting Rod Bearing .001 - .003 (.0025 prefered)

[donsjave]

I recently did my 401 (well okay, last spring) and I managed to find a Machine Shop that would follow the specs as outlined in the Tech Manual as put out my AMC. I ran as tight as the specs allowed and have suffered absoultly no problem at all.
The specs follows what the factory had done. There is one very important issue here and that the bearings (both rod and mains) must be tight or the result will be devasting to the engine. For example: a 360 that was done by a shop used the GM specs of .0025 for the rods and mains. This engine gernaded in 2500 miles. I am talking from experience because I did it and I destroyed it on a chasis dyno. It was after the dyno that I realized that the shop did not follow the tech manual for AMCs but rather that of some GM book.
I strongly urge anyone who owns a AMC to buy the tech manual for any particular year. The manuals are invaluable and a real good source of information for they were written by the people who put out the cars. It would the best money spent for any AMC enthusists.

[javelinjeff]

got to agree with Big Bad AMX and Donsjave on this one,had a 68 with a 343 back in 1986 that had a good tight motor and oil pressure was never an issue,even when hot.now the smoking rear tires and the Sherriff's Dept, that was another issue.as to another one i assembled using a "rebuild kit" from the local auto parts store, it only saw 50 p.s.i. when COLD start-up.best was 20 p.s.i. at highway speed when warm and about 5 p.s.i. at idle.so i ran valvoline 20-50w racing oil in that motor along with STP oil treatment.probably was close to 90w gear oil with that blend.motor lasted about 40k before becoming a smoker.and of course i did NOT check bearing clearances on that "rebuild" kit,using "standard" size rods and mains.and yes we were reading about oil filters and oil pressure relief/bypass modifications that never seemed to answer as to WHY oil pressure was low 21 years ago.Larry Mitchell's experience kinda gives you the notion that he has been down this road long before he decided to run in any of the events he has done so i'll put the house payment on his advice---just my opinion

[Javelin360]

The specs I posted above came directly from the AMC Technical service manual for the 74 model year vehicles. I spoke at length with the rebuilder and was satisfied he knew the specs I wanted. I'll know in a few weeks if things are good when I get everything buttoned up and back in the car.

[donsjave]

The specs I posted above came directly from the AMC Technical service manual for the 74 model year vehicles. I spoke at length with the rebuilder and was satisfied he knew the specs I wanted. I'll know in a few weeks if things are good when I get everything buttoned up and back in the car.
I am not doubting you at all as to where the specs came from, just that the tighter the clearances are, the better off you are.