Low oil pressure at highway speeds, good pressure in streets

[64 200 ranchero]

i think stock oil type is 15/40w, my engine does the same thing, it will go from 50psi when it is cold to 30 when warm and 20 to 15psi when i have been on the freeway doing 3500 rpm for at least 20 minutes and going to idle , im sure my bearings are worn a little but it is still ok, my driving pressure on the freeway only drops right under 40 psi

 

[RASEC66]

Ok, finnaly got it in the shop and checked clearances they are as follows:

rod bearings: 3 thousandth's
main are 10 thousandth's under
and there is at least 4 thousandth's clearance

the mechanic said that the mains is where the oil pressure is going but he could not find an over sized bearing to reduce clearance... he said it might need a crank kit if we cant get the right bearings. does anybody know of bearings that would work?

also im thinking a high volume oil pump might make a difference. Who sells H.V. pumps for the 200?

Thanks!

 

[bubba22349]

If they are used bearings than replacing them might tighten it up enough to work. You need around .0015 to .0025 as max for street engine, .003 could work for a race car don't use light weight oil with clearance like that. If the bearings are new than you will likely need a fresh reground crank to fix it. They don't make HV oil pumps for the 200. Good luck

 

[MPGmustang]

wow, low oil to engine rebuild... good thing it didn't blow up... good call.

I agree on the clearances making your oil drop presure. IMO, get her done, once and right.

I've always wanted to look into oil pumps but there is not many accurate pictures of them online yet. so we don't know if ANY can cross fit. I know my dads 40 packard running 15psi (stock in manufacture book) is now using a 72 pontiac pump and gets 45psi, I just don't think anyone has taken the time to track anything down for a HV replacement.

 

[RASEC66]

So I thought the clevite bearings Mike sells were under sized but it turns out they are over sized so I hope I can get the right size from him.

Am I right? over sized bearings will reduce clearence therefor giving better oil pressure?

 

[RASEC66]

aa man so my mechanic talked to Mike and they figured out that the 10 thousandth's bearings are too small and the 20 thousandth's are too much. so it needs a crank kit.

anybody done this before?

 

[RASEC66]

how big a difference is there with 20w 50 to straight 60 weight oil? thats the only one I have not used.

Thanks

 

[69.5Mav]

What are you trying to accoplish?

How did the shop measure the clearance?

Cranks can be reground to fit available bearing sizes.

Rod bearings come in STD, 1,10,20,30, 40

Main bearings come in STD, 10,20,30, 40

If your bearing are that loose then the bearings, which are soft, are more likely to be worn out then the crank journals.

I have successfully replaced worn out rod bearing. If the crank journals are still good I would get some new bearnings and fit them up using Plastigage to check clearance. All bearning are manufactored to a tolerance. This means that some are thicker then others. This means that you can switch them around to get the correct clearnce, sort of mix and match.

 

[bubba22349]

I have used straight 50 weight racing oil in a drag only car, and have also used 60 in old worn out street engines to keep them going a little longer. It's a crutch though and not the best practice for a new motor or a street car you need to use as a DD.

 

[woodbutcher]

Hi all.Inoticed in perusing this thread that it was mentioned that the crud found in the oil pan could plug up the oil passagers in the block.But IIRC the oil goes from the oil pump to the oil filter first before going to the rest of the oil system.Seems like the filter would catch the debris.If there was crud in the block,perhaps the machine shop did`nt do a good job of cleanung before AND after the machine work.If I am wrong,please correct me.Thanks.
Good luck.Have fun.Be safe.
Leo

 

[oldgrezmonke]

The debris mentioned included pieces of silicone . Excessive use of silicone can result in gobs of it blocking the drain back holes which restricts the return of the oil to the pan to be recirculated . Overly restrictive drain back holes [a factory mistake] were what killed the engines in Chevy Vegas in the 70s to illustrate the importance . Sloppy use of silicone also raises questions about the rest of the rebuild process .

 

[RASEC66]

Wow its been a long and busy semester, turns out my rod and main bearing clearences were way too high, so they went through the engine and line bored it. now it does not knock and the oil pressure stays above 20psi, yet the lifters start making noise once it does drop to 20 psi. Its weird, it keeps around 40psi for a bit, then suddenly drops to around 20 psi, when the lifters start making noise. I then just drop it into neutral and the pressure spikes back up to 40! I do that throughout any highway drive! its rediculous! 20psi should be enough to keep any noise from happening right? also why would it be dropping all of the sudden then spike back up if I change gears?

all of the mechanics in this town have yet to find the problem.

at least it does not knock tho.

 

[Soldmy66]

Have you replaced the oil pump? What oil are you running? Are you certain you have the correct dip stick (i.e. are you sure you are using the correct quantity of oil)?

Normally, the 200ci does not need a high volume pump, but you can look into those and also look into shimming a stock pump. I am not advocating shimming a stock pump, because I have not personally done it.

 

[chad]

U sure that's what the sound is. Other things can sound like that...

 

[RASEC66]

soldmy66- ya its running rotella 15w40 right now and the pump is new and works. I dont think there is any high volume oil pumps out there for the 6er or else Mike would already be offering it. it has a stick pan and original dipstick. always use 4.5 quarts. Shimming? thanks!

Chad- no im not that sure but it sure sounds like that and since they are hydraulic lifters well its more likely to be them right? can I just go solid lifters on this car?

thanks!

 

[stu in wichita]

Early in this thread you mentioned that you had about a quart too much oil in the engine. Did the oil pressure drop on the hightway while it was overfilled? Or did that start when you corrected the level? As others have suggested, this sounds a like it might be inadequate oil drainback.

On some engines, at high rpm too much oil stays in the valve cover and elsewhere in the engine and can't get back to the pan fast enough. The result is that the oil in the pan is too low for the pickup, and oil pressure drops. This is a fairly common design problem on certain engines (2nd gen AMC V-8's for example). On these engines, a rebuild nearly always includes enlarging and/or adding drainiage passages. The same thing can happen on any engine due to blockage in oil drainback passages.

On some engines the easy cure is to run an extra quart of oil. That's okay for some engines, but no good for others. Too much oil can cause problems such as oil aeration and excess windage. Too much oil won't hurt the oil pump.

Still, maybe it's worth looking into.

-Stu

 

[Soldmy66]

I don't recall; have you verified the oil pressure sending unit is working properly?

 

[thesameguy]

I agree - what you're seeing as 20psi and noise could be 0psi and noise... I would definitely double check oil pressure with a new/good sender+gauge.

 

[RASEC66]

Ya we have tried putting an extra quart in there but that was before the rebuild. has anyone with the aluminum head from mike haad this problem? im currently using a proven good mechanical gage from the mechanics. the oil pressure drops but not to 0 meaning the drainback is still ok? but why would it drop so suddenly from 40 to 20 I feel like something straigh fails or something to the matter... why would lifters clatter at 20psi?

 

[292fan]

Just a thought, but how is you oil pump drive shaft. A possibility is that an end is worn and slipping at high rpm(freeway speed) and shifting into neutral reduces engine speed enough for the shaft to catch starting the cycle all over again. Maybe a good idea to check the distributor and pump drive shaft.