98.5 blow-by?

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inline only

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Aug 5, 2008
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A friend of mine, has a 98.5 that lost oil pressure the other day and it ended up being 8 quarts low on oil, He was on a trip on the interstate and it pushed all the oil out the blow-by tube. The truck runs great, no missing but has excessive blow-by, I read another thread on here of a leak in the vacuum pump being bad causing blow-by. I removed the hose from vacuum pump and plugged it off. Still had blow-by, I checked compression and all cylinders are 380-390. What can be causing this problem? He also says that the engine oil pressure is running alot higher than normal, is that from the crankcase being pressureized? Any help would be appreciated. Stock Turbo appears tight also. truck only has 134k miles and does not appear to be a 53 block
 
Surely someone has seen this? It seems to me maybe the vacuum pump has an internal leak and is creating a crankcase ventilator pump. it has enough blow by that it hits the ground when warm but seems to be just steam, doesn't have much pressure though when I pull oil fill cap off, if you hold the throttle wide open it will start pushing oil out the tube. Truck starts as soon as you hit the key and i would think with a head gasket issue it would show up on the compression test. truck is stock besides 120hp injectors
 
un bolt the vac pump from the engine and see if it still has the excessive blowby. Just put some thing over the hole to stop the oil from running out. HG wont always show on a compression test depend on how bad its blown. Figure a comp test is only around 400 psi where operating pressure is 4-5000 psi
 
You say he has high oil pressure. That could be a stuck pressure relief valve in the oil filter housing. I have seen this before. Several times.
 
Running it that low on oil could have caused some major damage in the bearing. Could have trash in the relief valve.You need to pull the oil filter and cut it apart to see if there is anything in there
 
The filter was cut apart and no metal found, I do believe the pressure regulating valve on filter housing was stuck causing the high oil pressure, it is better now. I'm going to put a mechanical gauge in to actually see what it is running for pressure but according to the factory gauge with cold oil it runs around 100 psi and is never below 60psi at idle with hot oil. What is normal pressure for these engines? I don't think the truck ran hardly any without oil pressure as he was right by an off ramp and coasted it to a stop. I also didn't realize that cylinder pressure was that high and could see how it could be a head gasket issue, maybe blown over to the push rod holes? Also it has blow by pressure when engine is cold but you can't see the steam till the engine is warmed up good.
 
Mine when its warm runs about 40. What weight oil did he put in it? The heavier the oil the more the pressure goes up. I put 20w-50 in mine once and it ran around 100 cold and 60 hot. You could also run a leak down on it to see if its bleeding pressure before pulling the head
 
I've put 140 psi in cylinders and they do leak down fairly quick and it was difficult to determine where the air was going but seemed to be the crankcase. I figured it was normal for that to leak off and be able to hear it some? So do you think I should still pull the vacuum pump off and run it or just pull the head? He was running 15/40 mobil delvac
 
Were the valves closed when you did the test? It shouldnt leak down but maybe 4-5% if its leaking off fast you have a problem. So if you put 140 in it shouldnt leak down on the 2nd gauge to any less then 135 for it to be 5%. 10% would be 126 psi. What did it leak down to? You have to read the 2nd guage with air going into the cylinders.
 
I don't have the correct cylinder leak down tester, I had the rocker arms off, I just let air in from my compressor and closed the valve. So probably not a good test.
 
No not a good test at all. Actually not really even a test. You can probably rent one from your local autoparts store
 
I pulled the vacuum pump back and plugged oil line. Blocked hole in timing cover and still has pressure on crankcase vent tube. I checked oil pressure with gauge, at cold start on 60 degree day it has 80 psi at idle and 130psi at 2k rpms. WOW thats alot. I removed the external relief valve and it slides nice and free. Oil pressure of coarse comes down as the oil warms. Do I have 2 seperate problems or is one creating the other. Guess I was hoping someone had this exact same problem, I'm gonna pull the head if no one has any other ideas.
 
2 seperate issues. Is he sure he put 40 weight oil in it? I would recommend changing the oil and see if the pressure stays up. Also what filter dose it have on it the finer the filter the more oil pressure? Crank case pressure can only come from a hand full of places. Piston rings, head gasket, valve guides completely gone or vacum pump.
 
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What is the PSI of the oil when up to operating temp. The bypass valve is on the inside of the filter housing. You have to take it off to get to it.
PM me if you want the part numbers to fix it.
 
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