I recently bought a 79 Bronco and its been sitting for a while. I changed oil in it and wix filter. Added a little seafoam and STP oil treatment as well. I added a mechanical autometer oil pressure gauge as well. My problem is when I start it when its cold it has great oil pressure 75 psi. When it warms up the oil pressure drops to around 10 or 15 psi even when I am driving it around 35 40 mph. The oil pressure never goes up. What could this problem be? It doesnt smoke or make any lifter noise or anything. Any help or advice would be appreciated.

 

Sounds like the bearings and oil pump are worn. Almost worn out. Was this supposedly a rebuilt engine or is it original?

 

mmmmmm, rip the sump off and check a couple of bearings. If you did that and they were fine a new oil pump which isnt that expensive would be worth a shot. A work colleague told me a story a while back about his 351, he had the sump off for some reason on his vehicle (to do something with the trans I think) and there were big metal shavings in his sump. Turns out it was the cam bearings. It had been sitting around quite a lot and engine oil can turn acidic if left over time. it ate the bearings and they fell out! He didnt comment on oil pressure but the light obviously wasnt on and there was no mention of actual pressure so suggest there was no gauge.
suprised me but something to be aware of, they are cam priority oiling and they cant be done in situ
Lifters bores also have a lot to answer for apparently if worn. Good luck

 

Thanks for the replies guys. Ya the engine was supposed to be rebuilt. It runs so good when I bought it and didn't think the gauge was working. This is a big bummer and not sure if its even worth opening the pan to look. I might just start looking for a different engine.

 

These engines can run on 5-7psi with no questions asked. I'd run it until you find a killer deal or it seizes (which I bet would be a good while).

 

He could pull the pan and look at the bearing inserts. New bearings and an oil pump could buy him quite a bit of time, even if the cam bearings are marginal.

Just running it with low OP, he could lose the block along with everything else.

 

^^^Agreed...I'd much prefer make the repair...but the psi he's running at now isn't that big of a concern in this particular engine family.

 

Murph, I am gonna bump your thread here little...

I just replaced the rods and main bearings in my '78. Before the I did that my oil pressure was barely on the (stock) gauge. After I swapped in new bearings (both STD and plastuigauged in tolereance) my oil pressure gauge was alomst pegged at its MAX (water was too for that matter).

I have had the cluster in and out chasing bulbs, so I decided to go with new mechanical water and oil pressure gauges. On the new gauges, water temp is normal (190 after warm up and stable), however at cold idle my oil pressure read 75 PSI immeadiatley on start up. Even after driving for 30 to 45 mins it only drops to 55 to 60 PSI (70 at 3000 rpm). I am running 10w-30.

This the highest I have EVER seen a 400 run oil pressure. Is too much a bad thing? Or does it sound about right to folks?

 

Dasher, When I rebuilt my 400, I went with a standard pump with the moroso HP spring. After about 1000k's of running, with the odd thrash (not that odd), it is now running about 80psi warmed up at cruising (I have a gauge in KPA not psi-got it free so in it went!).
Start up cold it's at approx 108PSi and when I first built it, it was at approx 120psi from cold! Actually popped the oil filter o ring, had to take it off to check and refit but tight. I am running Castrol GTX2 10w-40.
I have since read in certain places that too much oil pressure is a bad thing and that had me a little worried. Too late now. I can well understand if there is a problem with too much pressure, but I suppose I wasn't so concerned as I work with deisels that get up around the 100psi mark. Your limits are fine and considering Clevelands historical poor lubrication, I would be telling anyone who will listen LOL.

 

Thanks for the reassurance crsmiffy. I geuss I will just run it till it blows, some things a guy just can't get worked up about.

 

Get on tim meyer website. read on cam bearing upgrades. has a simple solution for your potential new upgraded engine. the clevelands/400/351 had some issues but they are easy to upgrade at a fair price. tim has a simple solution and when rebuilding a engine have to buy cam bearings anyways and spend a buck or 2 more and have upgraded bearings. the next level would be to thread/tap restrictors in cam lube holes. tim meyer has a good read and simple catch you later.