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4.6 Stroker loses oil pressure after running high rpms

S

seanyb505

NAXJA Forum User
Location
Simpsonville, SC
I only noticed it after the initial breakin period, not during. I switched to Brad Penn 10W30 Racing oil at 1100 miles, and am using a mopar oil filter. Ive used the same brand filter ever since the engine first ran, so I dont think its that. I used 30wt breakin oil all during the first 1100 miles, so I dont think the oil is too thin either. I only noticed the drop in oil pressure when Ive sustained higher than grandma rpms (highway cruising at 85ish) and hard acceleration when the temp is a little high. (Stop and go traffic, traffic light to traffic light). The only time it will drop is if I come to a complete stop and the engine has 5 seconds to idle. As soon as I bring the rpms up a little the pressure returns to 10ish psi only to fall again if I let it idle again. If I stop and dont let the engine idle at 750 but keep it at 1000 it will not drop. Im wondering if I should go to a different oil, oil filter, or if i need to replace my standard flowing oil pump for a high volume unit. Ive also heard of shimming the spring in the stock piece, would this help at all? Any ideas?
 
Awesome, I was hoping I was going to get to take the oil pan off lol. It was the same pickup tube and oil pan from the stock engine, just a new standard flow oil pump.
 
was the stock pump cleaned out? an HV pump wont really help you any since the motor is not starvin for oil when it is running right. I have a big stroker and run an OEM pump, which reads 45 to 50 while driving and settles at 35 to 40 at idle. I would go with something being wrong at the pick-up.
 
Have you checked your gauge?

I had a sender go bad and give crazy low pressure readings.

Good Luck

Nick
 
Mine did this. My problem is in the wiring harness for the stock guage. I was worried with LOW oil pressure at idle and fluxating oil pressure in higher RPMs etc. So I checked it with a mechanical guage. I have 25psi hot at idle and it gots up to 60ish and stops(pump bypass I assume) when revved up. Its been about 3 years no and the stock shit still swings around and sometimes reads zero no matter how many oil pressure senders I swap out :). Hope thats all it is. Check it with a mechanical guage before you pull the pan!
 
I dont think I spun any bearing. Ill look into getting a mechanical gauge wired into the cab if the wiring harness is screwy. It goes crazy with the gas gauge too, but Im not so much worried as I keep a tab on the trip meter so I dont run out of gas. Id rather not take the chance with oil pressure.
 
if the gas gauge is having a problem while the oil gauge is also, i would think its an electrical problem with the cluster.
 
Im guessing the culprit (without having investigated the inside of the oil pan) is that I have 10w30 racing oil in there and its getting too thin when its hot. I will most likely be switching oil type on the next go around in 1500 miles. Untill then, Ill just not let it idle at stop lights. Has anyone had any experience with Lucas oil stabilizer? Is it snake oil?
 
I just ordered my second case of that oil. I would take the cluster out, ohm out the ground in the harness(after you checked the fsm--I can track down the wire if you want), inspect the ribbon on back of cluster for wear/rip, make sure screws are tight, reconnect the harness and see if it's better.
 
Did you check your oil clearances before assembling the engine?
I run BP 10w30 in my 4.0 and I haven't seen it go below 30psi, so I wouldn't say that the oil is too thin, unless the clearances are on the large side. The Lucas oil stabilizer is some thick stuff and worth a try. If the clearances are on the large side it will keep the pressure up.
When you take the pan down put a piece of tape over the pickup tube and put a ball of play dough on the end of it and put the pan back up. Not sure how much room it had stock but I would be concerned if it was over 5/8 inch away. Don't forget to remove the tape from the pickup. You could add an extra quart of oil to it and re test it to see if the pickup tube is an issue before dropping the pan.
Does your local machine shop have one of the tools for cutting open the oil filters to inspect for parts of bearings?
Just to cover everything, Did you check to make sure all of your main bearings were the correct undersize and that all the cam bearings are the right size for their position?

~Alex
 
I didnt have much part in the actual building process, but I was told by the machine shop (which is reputable in this area) that they check everything before the slap it together. I had the machine shop measure the crank main and rod journals before I ordered bearings. It doesnt make sense because it IS only after I run it hard or at a higher RPM. Ive been grandma'ing it around town and havent gone over 65 and Ive had no issue. For the other guys running Brad Penn 10w30 did your case say racing on the side? I just want to make sure. Ill try the lucas stuff today, and pull the pan when I change the oil next time to be sure the pickup is correctly positioned.
 
Just got done driving it all over town. I made special effort to not flog it at all, and there was no drop in oil pressure, even when the temp went over 210 at idle. We'll just have to wait and see when the pan comes off.
 
I meant to say 1/4 to 3/8 of an inch is desirable for the pan to pickup clearance.

Also make sure the dowel pin is in place that locates the pump to the oil galley hole in the block.

~Alex
 
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