Low cylinder pressue
05-04-2015, 12:46 AM
#1
Thread Starter
Join Date: May 2015
Location: CA
Posts: 2
Low cylinder pressue
Hi all. This is my first post on this forum I'm hoping I'm in the right place. I have a 66 6 cylinder mustang. My dad had the motor rebuilt about 5 or z6 years ago and we have not driven it much since. Maybe about 10 miles or so. We did a compression test on each cylinder and they all came up in the 135-140 range which if I am correct is low. We discovered that one of the freeze plugs has a small leak. Just wondering if this could cause the loss of pressure in the cylinders? The only other thing I could think of is maybe the head gasket is bad? Thinking that the block shouldn't be cracked or at least hoping... Any info would be great!
05-04-2015, 02:54 PM
#4
4th Gear Member
Join Date: Nov 2013
Location: arizona
Posts: 1,398
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135 - 140 is typical and not all gauges are accurate . . if it doesnt smoke the rings and guides are go . . if the compression is within 10 lbs or less between cylinders, it is ok . . if it is not steaming white steam out the pipes, water is nor leaking into the cylinders.
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135 - 140 is typical and not all gauges are accurate . . if it doesnt smoke the rings and guides are go . . if the compression is within 10 lbs or less between cylinders, it is ok . . if it is not steaming white steam out the pipes, water is nor leaking into the cylinders.
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05-05-2015, 06:12 PM
#6
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Join Date: Dec 2005
Location: Hills of California
Posts: 5,208
is there any indication of the coolant leaking to say the ground or some place on the engine?
How does the oil look? Is it nice and gold / black (depending on the age) or does it look like a chocolate milkshake?
How does the oil look? Is it nice and gold / black (depending on the age) or does it look like a chocolate milkshake?
05-05-2015, 11:45 PM
#8
5th Gear Member
Join Date: Mar 2008
Location: wisconsin
Posts: 2,260
just in case u needed another post saying that those compression readings are normal.....here it is 
freeze plug leaks are normal on rebuilds, sometimes they dont seal on the first go, what i did on mine was to run some bars stop leak for a week, then flush the system, sounds hokey i know, but beats pulling the engine, been 8 years and still going with no problems. as far as low compression, thats not your problem, if u have any sort of driveability issues please update
freeze plug leaks are normal on rebuilds, sometimes they dont seal on the first go, what i did on mine was to run some bars stop leak for a week, then flush the system, sounds hokey i know, but beats pulling the engine, been 8 years and still going with no problems. as far as low compression, thats not your problem, if u have any sort of driveability issues please update
05-12-2015, 03:59 PM
#9
Join Date: May 2015
Location: Texas
Posts: 45
Pressure numbers are acceptable...no steam/smoke out the pipe...runs good...I think you answered your own question with the bad freeze plug. And where there's one there's probably more! Take a look at all of em and check for coolant leaks elsewhere as well.
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