Hi folks. I'm new here. At least for posting. I've been here many times gathering info on my girlfriend's Ranger, and y'all have been very helpful. Which is why I'm here now. It's an 02 xlt 3.0l. To make a very long story short, another person was driving it and it overheated. He pulled over to let it cool down and said when he started it back up, it ran rough. He towed it home and decided to change the water pump. Reamed off one of the long bolts... In shorter terms, I inherited a truck in pieces. Put it back together and started it up and sure enough, runs rough. Did a compression test; cyl1=90, cyl2=90, cyl3=135, cyl4=90, cyl5=0, cyl6=60. Don't know how hot he let it get nor for how long, but it appears to be a doozie. One question I have is; Is the 90 psi normal for around 135k miles? I understand the 0 and 60 readings, but the 135? Secondly, what are the odds it's much more severe than blown head gaskets. Didn't see any coolant in the oil nor blow by in the radiator. Thanks.

 

It should be at 160 PSI, even high millage engines will still be at 145 to 150.
Make sure you have the throttle open all the way when doing a compression test.

I'm also thinking that your compression tester isn't "seating" properly when screwed into the spark plug hole.
Having "0" compression on #5 is unheard of.
Crank the engine over a few times too, if you haven't already done so when doing a compression test.

At this point I can't say why the readings are so low and how an over heated truck can cause such low readings, that's why I have my suspicions that the test was done incorrectly.

 

Thanks, Jeff. I did crank the engine over a few times. I did NOT open the throttle. Will do that the next test. #5 hole was very difficult to get to. I ended up starting the adapter by hand and then tightening with a socket. Just snug. The readings looked so odd, I did the test three times.

If he drove the truck a distance, is there a possibility he burned a hole in the piston? Or burnt the rings up? The oil didn't have anything in it, but might there be a magnet in the oil pan?

 

3.0l Vulcan engine has 9.1:1 compression ratio and common multiplier is 18
9.1 x 18 = 163.8
so 163psi would be around what you would expect from that engine.

Yes, if driven overheated the metal expands beyond it's limits and starts to crack, heads are at the top so get hottest because coolant is lost from that area first.
The expanding head metal also crushes the head gasket between head and block.

So not a chicken and egg thing, if you drive overheated you blow the head gasket, head gasket doesn't just blow and then you get overheating.
So a $5 heater hose can run into a $1,000 repair bill if you don't shut off engine at first sign of overheating

Then you have exhaust valves, if driven overheated you can burn exhaust valves, literally melts away part of the valve, which would give you 0psi compression.

Hole in the piston could happen but is unlikely, that is usually caused by Pinging/Knocking, but engine WOULD start to ping and knock as it overheated so..............could happen.

All spark plugs removed
Push down on gas pedal while cranking engine, throttle open
Test cylinder and write down number
Add a teaspoon of oil to the cylinder and retest
If you were at 90 and with oil at 130, then yes rings are bad
If it just goes to 100 then rings are OK

I use a straw to add oil, dip it in a bottle of oil and put finger on its end, then put in spark plug hole and remove finger.

You can't test #5 that way
You could put #5 at TDC and then use a hose in the spark plug hole, blow thru the hose while some one listens at tail pipe, if they can hear or feel the air coming out exhaust valve is bad