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ponchotom89

Well-known member
Joined
Jan 6, 2012
Messages
97
OK I have a 78 Caddy 425 engine in my 37 Ford I`m building. I dont know how many miles are on it. My brother gave it to me for my 37 a couple years ago.I just got it to the point I could start it last summer.After putting a new set of wires and plugs on it it runs good.I installed a cheap mechanical oil pressure gauge and it would indicate about 40 psi cold and would drop to 20 after it warmed up.Now it starts at 20psi cold and drops about 5 psi after it warms up.To me this seems a bit low.I have a little lifter noise but nothing else.Is this typical of these engines or do I have the beginnings of a grenade?:confused:
 
don't think you have to be an expert on Caddy's..

40 cold start and 20 hot at idle are fine....I'd check the gage first.....might be it's just not accurate....shouldn't be any lower than 12 to 15lbs at idle hot...I've seen 10 but it makes me nervous....most idiot lights illuminate or will flicker at 10 or under....I'd check the gage first, with a known good one and then start thinking about an oil pump or bearings......I'd fix it long before it gernades....JMHO... if multiple lifters are clattering oil pressure is low, if it's only one, then might be a rocker or something simpler.....gotta check the pressure with a known good gage first...
 
I'd try another gauge first off... How much has it run since first starting it? If the engine had sat for some time, it may have had some built up crud that scored the oil pump after you ran it. Since the oil pumps on these engines are externally mounted, it's easy to swap, though they are not cheap...
If worst scenario comes true and the engine needs a rebuild, you would be needing a new oil pump anyways, so it may be worth trying a new one.
 
Take the oil filter off drain it cut it open and see if there's any metal flakes caught in the element. If not ZZ's right, If so jerk it apart flush the insides out, new oil pump, new crank and rod bearings, then no worries.
 
I dont expect it has run alot since it was taken off the road. I`m sure there`s alot of gunk inside.I personally havent run it more than a couple hours. I changed the oil and after it ran with the new oil in it the new oil is now BLACK.
 
The detergent in the oil is doing it's job. It will turn black for the first few oil changes if the motor hasn't been maintained or is newly rebuilt. Change the filter each time you change the oil too as it might be getting plugged up.

Go to Advance Auto or similar and buy one of the mechanical oil pressure gauges that sell for about 15 bucks. It will have an 1/8 inch npt thread on the back and with some Home Depot brass 1/8 npt nipples and couplers you can screw it right into the block where the sender usually goes. Put it in there and see what you read.

Cadillacs don't normally have super high oil pressure so 30-40 isn't bad. 20 is a little low, as is 5 psi, but see what you have first.

Don
 
Yep, Don is right....

Most oils are high detergent...could be reason for the noisy lifters...also as was stated that pump is external and cutting open the filter will tell you if there is metal...also drain the oil and look for a metalicy color...will also be a sign of metal getting into the oil.........maybe the high detergent is blocking up the oil pump pickup screen with sludge...could be several things but...either way, the gauge is the true test so I'd start there and then move ahead...Good luck and I hope it doesn't entail a rebuild....[P
 
Make sure you run a good quality oil filter such as Wix. The Cadillac engines have a problem with oil run back and if you use a Fram filter you will most likely have dry starts and the engine will make a lot of noise at start up. If you didn't change the timing chain I would pull the front of the engine apart and change it. When you do see how much of the nylon teeth are missing. It all might be in the pickup tube starving the engine from getting oil. That's how I spun a rod bearing in my first Cadi 500 engine. Oil pumps are really expensive for the Cadi engine and probably won't be your problem. Don't pull it off the engine until you've checked everything else. The thickness of the gasket between the pump and the block is really critical for correct oil pressure. There are several good big block Cadillac forums checked there for more information.

Keith
 
I'm in agreement that changing the oil pump isn't needed. It has very little to do with oil pressure, they either work or don't work. Put the 15 buck gauge on it first before you start throwing money at it and you will know exactly what you have.

Don
 
if you are getting lifter noise hot @ 5psi then you actualluy have low oil pressure. Most GM hydraulic lifters will start to tick @ 5-7PSI. But a quick ring and bearing (don't forget the cam bearings) and a good oil pump will bring it right back. GM states most of their engines will only carry 20psi stock, hot @ idle.
 
Ok here`s what I did. I found an old mechanical gauge in my "stash" don`t know what make it is(has an M on the face of the gauge) hooked it up and fired the Caddy up. The cold oil pressure started at 30, when it came up to running temp it dropped to somewhere between 10-15 psi.Is that acceptable?
 
I also have another"situation" with this engine.[S When I start it cold, with it idling,about every ten seconds, I get a loud BANG! out of the left bank header.After it comes up to operating temp it goes away.I suspect there`s an exhaust valve "hanging up" on the left bank.It`s actually pretty WILD there`s this BIG FLAME firing out the left muffler.:eek:
 
Ok.....anything that is near 10 when hot at idle....

I also have another"situation" with this engine.[S When I start it cold, with it idling,about every ten seconds, I get a loud BANG! out of the left bank header.After it comes up to operating temp it goes away.I suspect there`s an exhaust valve "hanging up" on the left bank.It`s actually pretty WILD there`s this BIG FLAME firing out the left muffler.:eek:

I'd fix the problem....but....I'd still find a known good gauge before I tear into it.....beg or borrow one but make sure 99.9% it's accurate.....until you know the gauge is good you are chasing your tail....that said, if it's only 10 at idle, I'd fix it, it will only get worse..JMHO as for the Big Bang.....does sound like a valve hanging up...are you still getting the valve train noise when hot???......with all the things you've posted...I'd be pulling the pan and covers and looking for the issues at hand...again JMHO....but I'm a bit anal about that stuff....:D
 
Keep in mind that Cadillac engines have huge journal sizes on the crank. Because of this they will run lower oil pressures than most typical engines. I just rebuilt my Cadillac 500 engine. It has new bearings and the crank was turned. I have about 40 psi at idle and the pressure drops to about 20 psi when it's hot at idle. From my understanding this is about normal. At driving speed the engine holds about 60 psi.

The Cadillac 425 that I just pulled out was running about the oil pressures you are seeing. It was a really tired motor but it actually ran really well. I drove it about 5000 miles over the year that I had it in my truck. It didn't burn much oil but it did make some rod slap noise when I first started it.

I would say as long as you have a new timing chain in it drive it. As far as the sticky lifter goes, I would drain your oil and then put one quart of oil in it and then fill it to full with diesel. Start the engine and let it idle for about ten minutes. Let it cool down and bring it back up to running temperature.
Change the oil and filter and see how it is. The diesel should clean out most of the crude inside the engine and hopefully end your valve stick.

Keith
 
I you feel more comfortable use more oil like one to one. We use one quart and didn't have any problems with it. It really cleaned out a lot of gunk.

Keith
 

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