96 blazer, 200K+ on engine. (Junkyard replacement, has a new high-volume oil pump) engine has plenty of power, not using oil, trans shifts fine, when pulling my 1,000 pound 6x10 box trailer, the shift points are higher, probly doesnt grab 3rd gear until 50 mph, just before it shifts and the rpms are way up ( no tach, dont know what the rpm is) the oil pressure guage drops from the 40/60 it normally runs, down to 20. As soon as it shifts and the rpms drop, pressure goes back to 40. Has less than 200 miles on the last oil change, pennzoil conventional 10w30, ac filter, truck runs fine otherwise, towing or not. Havent noticed a oil pressure change when not towing, should i be concerned? Not sure if a heavier oil is the answer, one thing though, the baffle in the oil pan had to be removed due to the larger oil pump i put in, not sure it would be related....but.? Any thoughts/comments/similar observations? Thanks!

 

Could be cause its getting warmer?

 

could be draining the pan at higher RPMs with the high volume pump. checked your oil level? bet it would doit sitting still if you revved it high enough

 

Oil level is fine, i thought about that, and considered overfilling the engine by a qt or two, but then you areate the oil with the crankshaft, that aint good either...

 

drain a qt out and add a bottle of Lucas oil stabilizer

operating temperature is likely higher and oil cooler working less efficiently
do you have a good mixture of water and coolant? 50/50

 

Flushed cooling system about 3 weeks ago, has fresh 50/50 mix fill (green antifreeze) today i pulled the trailer about 60 miles, if i gently accelerated it would maintain oil pressure, if i hit resume for the cruise it would stay in 2nd gear longer, oil pressure would drop at about 45/50 mph, once it went into 3rd pressure would come back up.

 

I think coolasice may be right. I had a well built pontiac 400 with a high volume pump. At the top of each gear the oil pressure would drop and when drag racing, this isn't a good sign at WOT. I was sure I was going to find metal in the oil. I did two things. 1) Got an oil pan with baffles and 2) Got the biggest friggin oil filter I could find. Problem solved.

 

Not sure how a bigger filter would help (doubt i could get a bigger filter for this chassis type) have to pull the motor to drop the pan, i might just have to not tow with it, dont want to spin bearings on another motor, my dad suggested running a heavier weight oil, i did notice that after i dropped the trailer, if i drove it hard it would do the same thing, drop pressure right before the shift when the rpms are high. Maybe it is putting all the oil up into the top end of the motor and it cant drain back into the pan quick enough.

 

bigger filter=more oil. 1/4 of a quart might be all it needs to not drop pressure at the high rpm. A remote oil filter kit mounted vertically with a large filter might solve your problem over the stock one or put a stock oil pump in it. I can see no reason to have a high volume pump in anything other than a race car and only if you got a a 7 quart pan. Because no matter how much oil is put out by the oil pump there is almost no pressure unless there is a resistance to that oil flow and the main resistance is from oil trying to flow through the bearing surface clearances and once the pumps output pressure exceeds the engines ability to accept the oilflow at the max pressure the oil return system/bypass spring allows the oil to circle back through the pump.

 

Well, the real reason i got a high-volume pump in the first place was cost, the original engine spun just anout all the rod bearings and both center mains. The junkyard engine i got had over 200K on it, thought i should put a pump in it along with new front/rear crankshaft seals. The original replacement pump was sold seperatly from the pickup sump/tube, the high volume pump came with the pickup tube/sump (and was cheaper then buying a stock pump and the pickup/sump) i figured it was the way to go, didnt know id have to do away with the pan baffle and remove some material from inside the pan to get it together.