Low oil pressure at highway speeds, good pressure in streets

[RASEC66]

More problemos, the last two times I got my car on the highway, once I hit 5th, the oil pressure drops and after a bit it starts to clatter, like there is no oil in the top end. Therefor making me stop, turn it off, wait a bit and then it is fine. but only for a bit. The temp stays good but the oil goes down. Im wondering if having too much oil in the engine would have made the pump go bad. It was a good quart over, 5.5 quarts instead of 4.5. Im performing an oil change and going to cut the filter in half see if there is some debre in it.

is the oil pum an eazy replacement?

Thanks for any thoughts.

Ps: have had to race a couple of miatas and Mr2's in town, with good results hahaha, having vaccum advance connected and working properly is a great plus. makes it eazy to throw out the tail end! not often tho... gas is expensive.

 

[bubba22349]

More problemos, the last two times I got my car on the highway, once I hit 5th, the oil pressure drops and after a bit it starts to clatter, like there is no oil in the top end.

is the oil pum an eazy replacement?

Sounds like you might need to look at your top end oiling and maybe do some cleaning of the oil passages and rockers.

Yes they are easy after you get the oil pan off.

 

[RASEC66]

So I replaced the oil pump, cleaned the pick up which was full of what seamed to be black paint pieces and silicone pieces, turned the car on, oil went to where its supposed to. took it out to the highway, ran well in 5th maybe 83mph, then let it criuse on neutral and the oil pressure just dropped and the same story. it was a 2 mile round trip, so I hope there is not much damage though it sounds like the rockers are the ones making the noise. This had not happened before, and now the pump is new. Ill clean the top end tomorrow and see how it looks.

what else would make the oil pressure drop like that?

Thanks for any thoughts

 

[bubba22349]

what else would make the oil pressure drop like that?

Very worn main and or rod bearings also worn cam bearings. Worn crankshaft journals, Oil pickup tube to close to bottom of oil pan, dented in oil pan.

 

[oldgrezmonke]

By the junk you found in the oil pan - I'd first check to see if the oil drain back holes in the head are clogged .

 

[69.5Mav]

I'd first check to see if the oil drain back holes in the head are clogged

I agree. If the drain back holes are pluged then all the oil will end up in the valve cover/head and none in the pan causing the oil pressure to fall off.
When you let the car sit for a bit then the oil get a chance to leak back into the pan starting the cycle again.

 

[RASEC66]

Yeah, Im going to remove the valve cover today and see what is up. the engine barely has around 3000 miles on it, the cam is new too, I was researching yesterday, and there were people having just about the same prob and it was resolved with a larger oil pan or a higher weight oil. Is 10w30 to light for a higher performance 200? It has the alluminum head and a 264 cam from Mike also. should I do a high weight oil change and drop in maybe 5.5 quarts instead of 4.5? maybe a straight 40 weight

thanks!

 

[wsa111]

Sounds like your engine is sludged up. Which is hard to believe if it was redone recently.
Put a quart of kerosine in the oil & run the engine for 15 munuites.
Drain oil & install a new oil filter.
Also if you pull the pan again which sounds like you will also check the screen to pan clearance.
You may have to pull the engine & steam clean the insides. While you are there check all the bearings.
You may have to have the block & head hot tanked to clean out the sludge.
If you luck out marvel mystery oil will clean the lifters unless the lower end is shot.
Best of luck. Bill

 

[RASEC66]

When I dropped the oil pan I saw no sludge at least on the low end. I had the head hot tanked and jet washed about 6 months ago and it has not seen many miles since. Would going to a different weight make a difference? maybe with an extra quart also? al this after cleaning the rockers and oil ways on the top.

Thanks for all the replies!

 

[bubba22349]

Was the bottom end rebuilt too? If so what kind of bearing clearances are you running? When you had the pan off did you happen to check the oil pickup tube to sump clearance? I don't think adding an extra quart of oil would help unless you also make the oil pan sump bigger to hold it (IE drop the sump or widen it) it's not good to over fill it.

 

[turbo2256b]

How was the block cleaned when rebuilt. Were the oil galley plugs removed and brushes run through them?

 

[RASEC66]

yes the bottom end was rebuilt also. wow I guess I dint know my rod clearances or if the galleys were cleaned. but this only started happening recently. the pick up clearence is good, pressure stands good until it gets hot, like after a 10 min drive. I also read theat 10w 30 is also a low pressure oil.

 

[JackFish]

What brand of oil filter are you using?

 

[MPGmustang]

wrong kind of oil?? I like to use thick oil for summer now, GTX 20w50 keeps presure up to 45psi with an rev, might go down to 35, 30 at idle and 20 on low idle.

what kind of gauge are you going off of? a mech? or the stock oil indicator... I saw a oil presure reading??? if stock oil indicator it could be going bad...

 

[RASEC66]

I always use Wix filters, and had castrol gtx 10w30 in it. I just did An oil change and put rottela 15w40 in it with a quart of valvoline conventional 20w50 and a new filter. didnt have a chance to run it though. I will tomorrow.

Im going off of the old indicator wich actually works pretty well, and also the fact that The engine clatters once it hits a certain level on the gauge. So it makes me stop and turn it off for a bit then the pressure is enough to get me home haha. I had most of the wiring redone only 3 years ago.

 

[80broncoman]

if the drain back holes are clear (use compressed air if you have to) then there is the possibilty that the the paintchips and silicone could be in the oil passasges as well.
You could (cross your fingers) remove the oil filter and hook a air hose to the oil passage that comes up to the rockers and see if you can dislodge whatever is in there.

 

[RASEC66]

funny story, went to clean the rockers and oil ways, removed the rockers and up came one of the pushrods, and with it the lifter... could not get it back in the hole with a magnet tool from the pushrod hole. Now I have removed the head once more! time for more compression and a better exhaust gasket. jet washing the head see if it helps.

 

[bubba22349]

Good deal that should help, are you doing a valve job too?

 

[69.5Mav]

and up came one of the pushrods, and with it the lifter

Did the pushrod get drawn up by the rocker arm assembly or was it pushed up by the lifter?

When removing pushrods I always use a sideways motion to break it loose from the lifter, ask me why, I had a side cover on that engine so it was not so bad to get the lifter back in place.

Also as long as the head is off it might be a good idea to have your machinest check the head.

Be sure to clean out the oil drain holes while the head is off.

 

[strat1960s]

Sounds like you've solved your problem. A few years back, when I had my motor rebuilt/port/polish and spin balanced, the machinist told me to use 5W40. He said when the motor gets hot (likes to run between 200 and 220) the oil thins out and pressure drops. The day I bought the oil for my first post-storage oil change I could only find 15W40. It's been a while and I don't recal if the 15 is thicker or thiner than 5W. My oil pressure, when the motor is warmed up drops to 15 to 20 psi. That always makes me a little nervous. Will change out the motor oil in a few weeks and will provide oil pressure updates.

Ted