The compression test found the problem cylinder.
Three cylinders reached 140 psi. Cylinder #1 stopped at 61 psi, and the open radiator added a coolant geyser to make sure I was paying attention.
Pressure measured in pounds per square inch
Mission: stop guessing and test the engine.
The wagon had become hard to start, stalled after getting hot, wanted to die at stops, smoked, and overheated even after the thermostat was replaced. The compression test did not finish the diagnosis, but it finally gave me a clear direction.
What the compression test tells us.
These are the shortest useful answers. The test found a serious sealing problem in cylinder #1, but it did not identify the failed part by itself.
What did the test show?
Cylinder #1 measured 61 psi twice. Cylinders #2, #3, and #4 each measured 140 psi. That makes #1 the clear outlier.
Is 61 psi low?
Yes. The factory-style reference lists 100 psi minimum and no more than 25 percent variance under its specified test conditions. The 61 psi reading is below that minimum and about 56 percent lower than 140 psi.
Does this prove a blown head gasket?
No. It proves that cylinder #1 has a serious sealing loss. The wet plug, overheating, and coolant surge make a head-gasket or cylinder-head problem likely, but valves, rings, or piston damage are still possible.
Why test all four cylinders?
The other cylinders provide a comparison under the same gauge and setup. Three matching 140 psi readings make the single 61 psi result much more meaningful.
What comes next?
A leak-down test when work resumes. Listening at the intake, exhaust, crankcase, and cooling system can help locate where cylinder #1 is losing pressure. The engine stays off until there is a repair plan.
The spark plugs started the investigation.
I pulled all four spark plugs and kept them in order to compare the cylinders. Every plug looked very dark and sooty. The firing tip of plug #1 also had clear liquid on it, while the ceramic outside was dry. That was a clue, not proof of a blown head gasket — but it pointed somewhere specific.
Pulling the spark plugs
All four plugs came out for comparison before compression testing began.
Liquid on plug #1
Clear liquid on the firing tip. The outside of the plug was dry.
One cylinder told a very different story.
With the spark plugs removed, I tested each cylinder with a compression gauge. Cylinder #1 reached only 61 psi. I repeated that cylinder with the radiator cap installed and again with the cap removed. The reading stayed at 61 psi both times. Cylinders #2, #3, and #4 each reached 140 psi.
| Cylinder | Reading | Test Note | What I Observed |
|---|---|---|---|
| #1 | 61 psi | Same with radiator cap on and off | Clear liquid found on the spark-plug tip |
| #2 | 140 psi | Single recorded result | Dark and sooty spark plug |
| #3 | 140 psi | Single recorded result | Dark and sooty spark plug |
| #4 | 140 psi | Single recorded result | Dark and sooty spark plug |
Confirmed, likely, and still unknown.
What we know.
Cylinder #1 has a major compression problem. It measured 79 psi lower than the other three cylinders, which all matched at 140 psi.
Most probable cause.
Something is failing to seal around cylinder #1. Taken with the wet plug, overheating, and coolant eruption, a head-gasket or cylinder-head problem is the leading explanation.
What needs more testing.
The test does not identify the exact failed part. A burned valve, piston or ring damage, warped head, cracked head, or more than one problem still has to be ruled in or out.
What this explains.
What it does not prove.
No more running it just to see what happens.
The compression test narrowed the problem enough that continuing to run or drive the wagon could turn a repairable top-end problem into deeper engine damage. Before any teardown, there needs to be a realistic plan for the diagnosis, workspace, help, and cost.
Keep the engine off.
No driving, extended cranking, or warming it up for another test while coolant may be entering cylinder #1.
Make a plan with my dad.
Decide whether we can tackle the job together, where it can happen safely, and which parts require outside help.
Price the possible repair.
Account for gaskets, machine-shop inspection, replacement parts, tools, and whatever becomes visible after the head comes off.
Perform a leak-down test when work resumes.
Put cylinder #1 at top dead center on its compression stroke and listen for escaping air at the intake, exhaust, crankcase, and cooling system.
The mystery is smaller. The repair is not done.
I wanted the compression test to tell me that all four cylinders were healthy and I could go back to chasing something cheap. It did not do that. What it gave me was a real answer: cylinder #1 is where the mechanical problem lives. The wagon is parked while I figure out whether my dad and I can take on the repair together.
The full diagnosis update.
Three cylinders had 140 PSI. One had 61.
The video connects the test results to the spark-plug and cooling-system evidence, then explains why the project is paused.
See the complete evidence trail.
The compression numbers are one part of the diagnosis. The full page covers the hard starting, stalling, overheating, wet #1 plug, coolant movement, likely causes, and what remains unknown.
What supports this page.
The pressure readings, spark-plug condition, and radiator behavior are firsthand observations from this wagon. Published references supply the test procedure and comparison specifications.
Operation CHARM service-information archive. Used for the warm-engine procedure, all-plugs-removed setup, disabled ignition, wide-open throttle, 100 psi minimum, and 25 percent maximum variance. View the specification page.
Los Angeles Public Library's Chilton automotive repair database is a supporting service-information resource. Access may require a library card. View the library resource.
The connected evidence trail for the hard starting, stalling, overheating, wet #1 plug, compression readings, coolant movement, and current project status. Read the full diagnosis.
Follow the diagnosis.
Full Engine Diagnosis
The video, full evidence trail, current status, and repair-planning reality.
Cooling SystemCooling System Overhaul
The larger investigation into why the wagon overheats and loses coolant.
Owner Resource2.2 Turbo Survival Guide
A beginner-friendly guide to the systems and symptoms that matter on an early Chrysler turbo engine.
Project ProgressEverything I've Done
The honest record of completed repairs, paused investigations, and what comes next.
The test did its job.
It was not the result I hoped for, but it replaced a pile of guesses with one very specific problem cylinder. Now the wagon waits while I make a realistic repair plan.