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Discussion Starter #1
I noticed an oil pressure drop, and decided to check my oil. The dipstick measured perfect, and the oil is as clean as a whistle, however, when you take the top fill cap off of the valve cover it is a different story. Also, I notice it is blowing oil onto my intake manifold. At first I thought a head gasket, but the oil in the pan is clean. I have never seen this happen before. Anybody know what would cause this? It is a 1967 390. Take a look at the picture below. It is like this in both breathers.






 

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its condensation causing that..
not to unusual with these cars .. we don't drive them to much..
or mostly short distances...
warms up then cool off.. especially this time of year...
air is cool and damp..
as engine cools off , it draws that damp air inside..


on daily drivers ..
engine stays hot for longer time and being driven every day...
so that moister heats up and evaporate and get sucked out thru your pcv system , then blown out the tail pipe....:wink2:
 

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Yup, fairly common moisture coming into the crankcase.
you can try to reroute the incoming air to a dryer source or drive more and get the engine hotter.

Main thing to check on an FE with this issue is the springs on the rocker shaft. The moisture can rust the springs and they will break.
 

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Discussion Starter #4 (Edited)
Another piece of info, is I have fresh oil on top of the manifold, and I can't figure out where it is coming from. The oil pressure dropped from 70 to 25 also. This happened on a 20 mile drive to a car show. The motor never overheated at all either, so this has me baffled.

 

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Oil on manifold is most likely valve cover gaskets. Shouldn't be hard to find.

What is your normal oil pressure:
cold idle?
hot idle?
cold cruise?
hot cruise?

For a standard pressure oil pump 20psi isn't that far off for hot idle.
 

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Might be possible with that much condensation to plug some of the oil return. I noticed a lot less condensation when the cars went to the heated air cleaners so the ventilation to the crankcase was also warmed. They were not as pretty a chrome open element but they did a good job with the condensation.
 

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Discussion Starter #7
Oil on manifold is most likely valve cover gaskets. Shouldn't be hard to find.

What is your normal oil pressure:
cold idle?
hot idle?
cold cruise?
hot cruise?

For a standard pressure oil pump 20psi isn't that far off for hot idle.
When I first start the car it is usually at 70 psi. At a redlight in gear it drops down to 50psi. Otherwise it is always around 70 psi over 2000 rpm. That is why I was a little concerned with the drop because I have never seen such a low pressure on this engine.

I am going to pull the valve covers and see if anything makes itself known. I will check my PCV valve also.
 

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I found out what it was. One of the piston rings is bad
how did you come to that conclusion ..???


bad ring has nothing to do with oil pressure...
compression yes...
 

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change oil & filter, & look at the pcv system. & yes a broken top compression ring will give you a ton of blow-by that will overcome the pcv system with moisture, & push oil out anywhere it can.
 

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change oil & filter, & look at the pcv system. & yes a broken top compression ring will give you a ton of blow-by that will overcome the pcv system with moisture, & push oil out anywhere it can.
Agreed, but how does that effect oil pressure? I'm not saying anyone is wrong, I just have never seen that and don't see how it would be a problem.

I feel like I'd be looking more toward an oil galley plug (like the one behind the distributor) coming partially loose, thus killing pressure slightly but not totally.
 

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I feel like I'd be looking more toward an oil galley plug (like the one behind the distributor) coming partially loose, thus killing pressure slightly but not totally.
or maybe a sticking pressure relief valve in oil pump ??


mechanical or electric oil pressure gauge..??
if electric could be a faulty sender, that is giving you false readings...
 

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Discussion Starter #15
I just assumed it was related. I thought the piston ring would be the culprit of the condensation. Honestly I forgot about the oil pressure problem when I thought I had the condensation solved. It is an old Stewart Warner gauge. It does have an electric wire going to the gauge with the others. The gauge is a set with amps,oil pressure and water temp. I know the water temp was working because I kept checking if it was overheating on way home because I thought it was a head gasket at first. It stayed at 190 like usual and the car runs like it always has. I will see if I can swap out the oil pressure sending unit and gauge to see if it is 2 separate problems.

But does it seem like the piston ring would cause that condensation? I'm definitely going to have to do new rings on it. All cylinders were 150 and one was 120 I put oil in that cylinder and it went up to 150 like the others.

Also any opinions on pulling the piston from the top to do the ring and only doing one? Will that mess up the other cylinder compression by only doing one cylinder ?
 

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some of the milky condensation could have ended up in the oil filter & partially blocked it causing lower pressure. As for changing the ring? I would say give it a try. Pull the pan, & push the piston out the top. I would mark where the ring gaps are located on the piston & reassemble it the same way. One other thing, do you know the ring is broke? sometimes the rings somehow turn on the piston & the gaps line up with each other causing low compression & excessive blow-by, in which case all you have to do is turn the rings & stagger them. good luck.
 

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To get the intake off you will have to remove the push rods on both sides. To pull the pan on a 390 means you have to raise the engine and spend a lot of time under there -- get some good goggles.

If you can live with a 30 psi drop in one cylinder, I say, live with it!
 

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if it has many miles there will be a ridge at the top of the cyl. which will make removing the piston almost impossible unless you use a ridge reamer. the rings end gap orientation only matters at assembly as they rotate when the engine is running
 

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Discussion Starter #19
I started the motor today and the oil pressure gauge and tach were not working, so I think I am ok with the pressure problem. Also, I checked the dipstick today after running it and now the milk is in the oil pan, so I think I got lucky with the warning up top. Definitely a head gasket. The distributor gears were all covered also. So I am tearing the motor down now to replace these head gaskets. I am going to be so close to that one piston I think I might try popping that piston up from the bottom and replacing the ring while I have it all apart. I can post pictures of the tear down if anybody wants to see the progress.
 
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