2.5L ('98-'01) 80-75 PSI on all Cylinders (is this bad?)


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So I took my truck to go get the plugs, wires, and coils changed out and I asked if he could a compression test. I went to go pick up my truck and he said that all the cylinders were showing between 75-80 PSI. I said that sounds pretty low, he said that it's pretty common in older engines to have that low of a compression and that it isn't anything he would worry about. Your guys thoughts? Around 265,000 miles.
 


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Shran

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Does it run well? Those numbers are way low... if it doesn't run weird or have a severe lack of power, I'd suspect that his gauge is not working right.
 

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Anything below 60psi and an engine simply cannot even work. So 75psi would be a barely functioning engine. It would be missing, smoking, banging etc.

But compression tests are more about variation than actual psi numbers. I agree with shran that his guage probably just sucks but if the numbers were all still close I would not worry about it.

I may look for a new mechanic though... one with a functioning compression guage and an understanding that 75psi is not OK.
 
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Yeah man this engine runs just fine, I'm thinking the same thing his gauge must be off.
 

Dirtman

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Compression gauges aren't scientifically calibrated so it's normal to get some inaccurate numbers but say your guage reads 10psi low. It'll read 10psi low on everything so it doesnt matter when your looking at numbers of all the cylinders. You are checking variation between cylinders not the actual high psi rating.

But if my guage ran almost 100psi low... I'd ummm buy a new gauge.
 

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60 PSI may be the bare minimum for a cylinder to fire, but 90 PSI is the minimum for the engine to start on. Anything less won't give enough of a pop at cranking speeds to get her to kick over.

At 60-75 PSI the engine shouldn't run.
 

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I should do a compression test on my sickle bar mower sometime. I bet that thing has next to none... it will not start with the rope (it's an old Briggs & Stratton from the 40s with a wind-up rope.) But I can get it going if I spin it with a drill... takes a bunch of rotations but it'll eventually come to life. I had the head off a while back to clean up the carbon that was caked on everything and the piston actually moves side to side about 1/16" in the bore. I think oil leaking past the rings is the only reason it has any compression, and it is always followed by a pretty significant cloud of smoke.
 


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