Excessive Blow-by
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From: Iuka, Mississippi
Excessive Blow-by
I've seen a reference to excessive blow-by possibly being caused by a bad seal on the vacuum pump. I have a 97 model 3500 that seems to have gone from acceptable blow-by to excessive in a very short time. Any information on a bad vacuum pump seal causing blow-by would be appreciated.
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From: South Western New Mexico
If the blow by has icreased recently, check your oil for fuel contamination. Possibly change it and use a good 15w40, I like to use Mobil delvac or havoline ursa. There are other good oils that some people prefer. I don't want to start a debate.
I haven't experienced the vacuum pump seal failure yet.
How many miles are on it? What kind of mods have you done? what's the oil consumption? Do you pull a trailer? What kind of driving do you do?
I haven't experienced the vacuum pump seal failure yet.
How many miles are on it? What kind of mods have you done? what's the oil consumption? Do you pull a trailer? What kind of driving do you do?
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From: Branchville, Alabama
The test as comes from Cummins is to remove the pump, put a cover plate on the mounting hole and start it to check for blowby. The seal into the crankcase can cause blowby as can the pump not operating right.
Make sure that you don't have a massive vacuum leak on it as that will also cause it. The exhaust from the vacuum pump is into the timing case.
Make sure that you don't have a massive vacuum leak on it as that will also cause it. The exhaust from the vacuum pump is into the timing case.
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From: Montana
You can make your own blowby measurement tool for under $10. A blowby orifice tool is just a tee with one .221" (15/64-in) outlet (pipe plug with a hole drilled in it). Connect one end of the tee to the end of the blowby tube. Put a manometer on last tee outlet. That is your blowby tool. A simple manometer can be made by looping 6' of clear tubing with water in it half way. Measure how high the water level rises with a tape measure, multiply it by 2, convert it to LPMs
Rough conversion is:1"= 27 lpm, add 3 lpm for each one inch (1/2'' of rise in the tube) of water
New engines numbers are;
63 liters per minute(2.5" water rise = 5" of water) @ 2200rpm,
76 L/Min (3.5" rise) @ 2500rpm
85 L/Min (4.5" rise) @ 2800rpm.
Worn engine that needs rebuilding are roughly double i.e.
126 L/Min(10.5"rise) @ 2200rpm
152 L/Min(14.5"rise) @ 2500rpm
170 L/Min(17"rise) @ 2800 rpm
The valves could also be out of adjustment.
The way I do it, same idea, is to block the blowby tube with a 1/2'' pipe nipple with a cap that has a 15/64 hole drilled in it. Use 3/8'' id looped clear tubing with water in it slipped over the oil dipstick tube. Use sharp tipped felt marker to mark the water level with the engine off, have someone start an already warmed up engine and run the rpms up to 2.2, 2.5 & 2.8k rpms. Mark each water level with the pen, measure then multiply each by 2.
This is all very simple to do, just hard to explain with words.
Rough conversion is:1"= 27 lpm, add 3 lpm for each one inch (1/2'' of rise in the tube) of water
New engines numbers are;
63 liters per minute(2.5" water rise = 5" of water) @ 2200rpm,
76 L/Min (3.5" rise) @ 2500rpm
85 L/Min (4.5" rise) @ 2800rpm.
Worn engine that needs rebuilding are roughly double i.e.
126 L/Min(10.5"rise) @ 2200rpm
152 L/Min(14.5"rise) @ 2500rpm
170 L/Min(17"rise) @ 2800 rpm
The valves could also be out of adjustment.
The way I do it, same idea, is to block the blowby tube with a 1/2'' pipe nipple with a cap that has a 15/64 hole drilled in it. Use 3/8'' id looped clear tubing with water in it slipped over the oil dipstick tube. Use sharp tipped felt marker to mark the water level with the engine off, have someone start an already warmed up engine and run the rpms up to 2.2, 2.5 & 2.8k rpms. Mark each water level with the pen, measure then multiply each by 2.
This is all very simple to do, just hard to explain with words.
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Joined: Nov 2001
Posts: 4,199
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From: Branchville, Alabama
Originally posted by infidel
You can make your own blowby measurement tool for under $10. A blowby orifice tool is just a tee with one .221" (15/64-in) outlet (pipe plug with a hole drilled in it). Connect one end of the tee to the end of the blowby tube. Put a manometer on last tee outlet. That is your blowby tool. A simple manometer can be made by looping 6' of clear tubing with water in it half way. Measure how high the water level rises with a tape measure, multiply it by 2, convert it to LPMs
Rough conversion is:1"= 27 lpm, add 3 lpm for each one inch (1/2'' of rise in the tube) of water
New engines numbers are;
63 liters per minute(2.5" water rise = 5" of water) @ 2200rpm,
76 L/Min (3.5" rise) @ 2500rpm
85 L/Min (4.5" rise) @ 2800rpm.
Worn engine that needs rebuilding are roughly double i.e.
126 L/Min(10.5"rise) @ 2200rpm
152 L/Min(14.5"rise) @ 2500rpm
170 L/Min(17"rise) @ 2800 rpm
The valves could also be out of adjustment.
The way I do it, same idea, is to block the blowby tube with a 1/2'' pipe nipple with a cap that has a 15/64 hole drilled in it. Use 3/8'' id looped clear tubing with water in it slipped over the oil dipstick tube. Use sharp tipped felt marker to mark the water level with the engine off, have someone start an already warmed up engine and run the rpms up to 2.2, 2.5 & 2.8k rpms. Mark each water level with the pen, measure then multiply each by 2.
This is all very simple to do, just hard to explain with words.
You can make your own blowby measurement tool for under $10. A blowby orifice tool is just a tee with one .221" (15/64-in) outlet (pipe plug with a hole drilled in it). Connect one end of the tee to the end of the blowby tube. Put a manometer on last tee outlet. That is your blowby tool. A simple manometer can be made by looping 6' of clear tubing with water in it half way. Measure how high the water level rises with a tape measure, multiply it by 2, convert it to LPMs
Rough conversion is:1"= 27 lpm, add 3 lpm for each one inch (1/2'' of rise in the tube) of water
New engines numbers are;
63 liters per minute(2.5" water rise = 5" of water) @ 2200rpm,
76 L/Min (3.5" rise) @ 2500rpm
85 L/Min (4.5" rise) @ 2800rpm.
Worn engine that needs rebuilding are roughly double i.e.
126 L/Min(10.5"rise) @ 2200rpm
152 L/Min(14.5"rise) @ 2500rpm
170 L/Min(17"rise) @ 2800 rpm
The valves could also be out of adjustment.
The way I do it, same idea, is to block the blowby tube with a 1/2'' pipe nipple with a cap that has a 15/64 hole drilled in it. Use 3/8'' id looped clear tubing with water in it slipped over the oil dipstick tube. Use sharp tipped felt marker to mark the water level with the engine off, have someone start an already warmed up engine and run the rpms up to 2.2, 2.5 & 2.8k rpms. Mark each water level with the pen, measure then multiply each by 2.
This is all very simple to do, just hard to explain with words.
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Joined: Oct 2002
Posts: 509
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From: Desert Northwest (Pasco WA)
I had blowby increase noticeably on my '96 although not that bad. I wasn't aware of the vacuum pump as being a source. I will have to check that out.
I did do the blowby volume test on my truck last summer, the results were 65 LPM at 2200 RPM and 83 at 2800. . . right there for a "healthy" engine. Truck had 351,700 miles at the time.
Vaughn
I did do the blowby volume test on my truck last summer, the results were 65 LPM at 2200 RPM and 83 at 2800. . . right there for a "healthy" engine. Truck had 351,700 miles at the time.
Vaughn
...the crankcase breather tube is dry as a bone, and not one whisp of steam puffs out the oil filler neck
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