Engine compression problem immediately following 100,000 service

When I took my 2005 Ford Ranger V6 to the local Ford dealer for its 100,000 mile service it was running fine and had no apparent leaks of any kind. Service included oil change, replacement of PCV valve, and replacement of spark plugs. They discovered a coolant leak, which was repaired, but reported no other problems. Within 20 miles of driving, I noticed very rough idling. Within another 30-40 miles, the engine was stuttering on minor hills, and acting like it was about to stall. Then the engine light came on. Back to the dealer, who suspected first a loose spark plug, then a bad spark plug wire, then found low compression in one cylinder. Dealer claims the problem is not related to the service work, and would have happened anyway. I find this very hard to believe.

Today they are pulling the cylinder head “to find out what the problem is inside the engine”.
Any thoughts out there? Talking points for me in continuing this discussion with the dealer?

Any normal maintenance procedures should not cause a compression problem. However, a cylinder head does not have to be pulled to find out what’s going on inside.

Any compression problem should be diagnosable without exploratory surgery.

Crackerjack, as far as I’m concerned, the burden of proof is on them to demonstrate why this isn’t their fault.

@ok4450 Yes, I recently had a colonoscopy (no problems found) and my head did not have to come off! A simple compression and or leakdown test, and, if necessary a borescope view to see what the inside looks like would reaveal what the problem is.

I have some doubts about this shop’s capabilities.

That loose plug was something they clearly should have properly tightened. I wonder whether they cross threaded that thing and are now going to cover it up by telling you that your head is leaking.

My gut suggests that you unintentionallly have only passed part of the whole story on to us. Where was the coolant leak? How was it found? For what reason did they say they need to remove the head to see what’s wrong?

I’d like the answers to these questions before placing blame on any shop.

Hey Doc, thanks for the laugh.


Read this


With all due respect, I don’t think the shop did anything wrong

Print out that document, bring it to the Ford dealer, show it to them, and ask them if they believe that you’ll be needing to buy some heads.

@RemcoW if you’ll read OP’s original posting, you’ll see that the dealer “suspected . . . a loose spark plug” OP did NOT state that the plug was indeed loose.

I’m not necessarily blaming the dealer either as one never knows how much of a story, details, etc. is missing.
It’s hard to fathom an engine running fine while having low compression and any valve seat recession that may exist did not happen in 20 miles.

The only quibble I have is removing a head as part of a fishing expedition but this possibly leads to another point.
The truck owner states that the dealer is in the process of pulling a head today. This means the truck owner approved the dealer pulling the head, or heads, after being given some disheartening news prior to that approval.

If the problem is valve recession problems then the truck was not running as fine as thought.


I certainly hope the mechanic working on OP’s truck is aware of that TSB

Unfortunately, when I was working at the Benz dealer, there were some guys that didn’t always check if a TSB existed that addressed a customer’s complaint.

@db4690 yes but first they did a “replacement of spark plugs.” So they must have tightened them. They then “suspected a loose spark plug”, one they should have tightened. Maybe they tightened it but cross threaded it so now it isn’t seated well. That’s what I’m saying.
I’d get a second opinion. Just because this is a dealer doesn’t mean they don’t screw up and also doesn’t mean they’re honest.


Maybe they did screw up, but a loose/cross threaded plug wouldn’t cause low compression . . .

FWIW . . . I’ve seen a number of 3.0 Vulcan heads with misfires caused by low compression. They all had slightly more than 100K. And I I verified that the problem was definitely top end.

Okay, I agree that a cross threaded plug may not necessarily cause low compression but do think it is suspect. Since potentially a bit of money is involved, I’d get a second opinion.

A lot of dirt can collect in the spark-plug wells after 100K miles…A careless mechanic can allow this debris to fall into the engine when he removed the old plugs…What happens after that is anybody’s guess…

Is nobody willing to give the dealership mechanics the benefit of the doubt?

Is anybody willing to consider that the TSB might actually fix the problem?

I don’t understand why they are removing the cylinder head, but I expect if they chimed in here they’d have a reasonable explanation. It’s perfectly possible the compression problem was already queued up, and would have occured in any event. The shop shouldn’t be held responsible for every problem that occurs after they work on it. That just isn’t fair. And if you think about it, that would be unworkable. Who’s going to work on a car when you end up responsible for any problem it develops afterward?

In an ideal world both the shop and the car owner would cooperate to find what’s going on. But if there is a burden of proof issue, in my opinion the burden of proof would be on the car owner, not the shop.

The OP may have a complaint with the car manufacturer, and might ask for some assistence there, provided they can document that all the routine service has been done and there are no obvious signs of misuse. Compression loss due to a faulty engine at 100K deserves some complaining, but not to the shop, to the manufacturer.

Perhaps they are removing the cylinder heads to visually confirm the “exhaust valve seat recession”

After 8 years and 100K miles, will Ford still pick up the tab on a pair of new heads and the labor to install them, should that turn out to be the problem…?

Given the “bad timing” the best one could realistically hope for is a modest discount

The TSB states that this problem is covered under terms of the New Vehicle and emissions warranty but that has long since passed as the TSB is dated 2005.

Even if FOMOCO was to look at it as a Campaign, odds are it would not be covered due to mileage and time.


If OP’s car truly needs the updated cylinder heads . . . and I believe they are needed, based on what has been stated . . . OP will be paying out of pocket

If nothing else, that TSB may help in the diagnosis.