over 200k miles compresion test?

[idn88]

The issue is not putting the plugs back in once they have come out cleanly. The issue is that if they have already been in there for 10 years they may be seized and take the threads with the plug or the plug can break and stay in the head if you pull them. If you don't know how long they have been in there anything can happen. Has nothing to do with a torque wrench, torque specs, or a mechanic not knowing what their doing. If there stuck, there stuck - and you almost never know until their broken or the threads are wrecked.

If your pulling the plugs for the owner its a whole different deal. If your pulling plugs for a third party thats thinking about buying the vehicle, who pays to fix the threads if they come out? For sure its not going to be the person paying for the inspection - there just going to walk. The owner isn't going to pay. So the mechanic doing the inspection is holding the bag. Like I said, high risk, low reward - why do it. I wouldn't.

 

[Goshawk]

Sure the owner is going to pay. Failure to maintain an engine by having the plugs pulled for regular service is still the owners issue. I sure would not want to buy a car with seized spark plugs. Don't think anyone is wrong to want it done before buying an engine. Effectively that engine is crap if you can't pull the plugs. So who gets to find out? The previous owner who failed to maintain it? Or the new potential buyer who is now stuck with a junk engine that can't be serviced.

Guess I have a new question for the owner. "When was the last time you changed spark plugs?" If there is no evidence it was done in the last two years then walk away. Paper evidence would be good on anything with an aluminum head. At least it's a start.

 

[ascii_man]

Sure the owner is going to pay. Failure to maintain an engine by having the plugs pulled for regular service is still the owners issue. I sure would not want to buy a car with seized spark plugs. Don't think anyone is wrong to want it done before buying an engine. Effectively that engine is crap if you can't pull the plugs. So who gets to find out? The previous owner who failed to maintain it? Or the new potential buyer who is now stuck with a junk engine that can't be serviced.

Guess I have a new question for the owner. "When was the last time you changed spark plugs?" If there is no evidence it was done in the last two years then walk away. Paper evidence would be good on anything with an aluminum head. At least it's a start.

This was probably a reasonable view in the past, but two things have changed on the engineering side: 1) spark plug change intervals have increased and 2) Ford built a ton of engines with poorly-engineered spark plug holes; see: https://vanlivingforum.com/Thread-Info-On-Common-Vans?pid=178948#pid178948

Moving on to the business / legal (IANAL!) aspects, I think it would be a difficult case to prove "well they should have maintained the engine better", given that many people don't follow the schedules religiously (I do and wish they would, but whatever), the plugs often seize if you do, and compression testing is not part of the typical intended use of the engine.

If you are touring a house and the master bedroom doorknob comes off in your hand, a reasonable person (legal term) would interpret that you were a reasonable person employing the doorknob in its intended use and you would be fine. And maybe if an FAA-licensed A&P mechanic did a test on a certificated aircraft you could point to mandated maintenance schedules and such. Since oil changes and oil level checks are frequent recommend service procedures, you're OK if something breaks off while you are trying to look at the color of the motor oil. But when you request an intrusive diagnostic test which is neither part of routine operation nor manufacturer's scheduled service procedures on a consumer-owned vehicle, you have a completely different animal.

EDIT: and in real life, nobody wants a long, drawn-out court case about this: you are going to have 3 angry men at a garage or maybe even at somebody's house with a nontrivial risk of violence. Owner: "You broke my van!" Mechanic: "I'm not working for free" (non-)Buyer: Not my problem!

 

[Goshawk]

You forgot. ---- Fooled chump buyer : the engine is toast and I have to live with it after 1000 miles.

 

[GotSmart]

So WD40 or other chemicals designed to loosen seized threads do not work on these plugs?

 

[VJG1977]

Old school test was to pull one spark plug wire at a time while watching a tachometer.  If the RPM's did not drop,  that cylinder wasn't firing or had low compression.

 

[Tinman74]

If I were the seller of a vehicle and someone wanted to pull the plugs and check the compression even if I knew the compression was fine I would tell them the vehicle was no longer for sale. Go somewhere else and buy your car. I don't know the ability of your mechanic and it is my car, leave your hands off.
Stuff happens!

Another Bob

 

[idn88]

Old school test was to pull one spark plug wire at a time while watching a tachometer.  If the RPM's did not drop,  that cylinder wasn't firing or had low compression.

On modern computer controlled engines if a cylinder was missing - even intermittently - the ODBC should pick it up and throw a code.  So if your compression was awful you should get a mis-fire code, along with a bunch of other emission codes.  This is the likely (but not guaranteed) scenario.  If your compression were just a little low you may get no codes.

 

[idn88]

If it were me - you know what they say about Opinions - I wouldn't be buying a vehicle with over 200K on it unless it had extensive service records that seemed, legitimate, and /or I was paying a very low price, hence an expensive repair which is likely at this age would make it worth while still, or if it was something early 80's or older - with steel block and heads and not a lot of computer control. And I would avoid certain vehicles with history of problems completely.

Everyone wants to pay a few thousand dollars for a really good used vehicle, however these don't much exist. The type that trade stuff in just because its older is fewer and fewer, a lot of those were shredded in cash for clunkers, and lots of people just don't maintain anything anymore. Those that do tend to keep their vehicles for a very, very long time and its an odd occasion to find something really well maintained for sale just because. In these situations they will likely be sold to someone that person knows before they ever end up on a lot or craigslist.

Even if you were to do a successful compression test on a 200K mile engine, it could just as easily have a ECM die, or spin a bearing, or whatever.

 

[Goshawk]

After all this discussion have finally resolved to just check codes and only consider vehicles with paper proof that they changed the spark plugs at some time in the past. Since compression is so invasive and risky.

 

[akrvbob]

Remember, it's only invasive and Risky with Fords who made a terrible engine and then wouldn't correct it. It's zero problem with Chevy or Dodge. I have a friend with a Ford 5.4 with 240,000 miles, she was driving down the road and it blew a plug, cost her hundreds of dollars.

The solution is don't buy a Ford with 5.4.
Bob

 

[eDJ_]

I once knew one old mechanic down at the corner gas station in my neighborhood who would disconnect the negative battery terminal and use a torque wrench at the front of the crankshaft. (in the harmonic balancer)  He would pull the engine all the way through and if it read between 60 to 90 lbs of torque consistently he figured it was probably OK.  The car was usually up on the lift.

He would then reconnect the negative terminal after making sure both terminals were good and clean and connect a clamp on meter to a wire at the starter and use a hand held remote starter switch to crank the motor while he read the gauge.  For this test he would pull the coil wire so the engine wouldn't start.  That gave his some other insights to the engine's condition.  

I've also seen him connect a vacuum gauge to an engine and check it.  He would accelerate the engine by hand  twisting the carb linkage and release it while watch the meter to see if there were any flutters of the needle.

But these three quick checks would let him know if ihe should spend more time pulling the plugs and doing a compression test. 

A lot of used car lots would bring trade in's to him for his opinion.

 

[highdesertranger]

just a heads up, it's not just the 5.4 motor ford had this problem with. basically they had this problem with all their gasser motors of this era in one form or another. maybe not as severe but none of their gasser motors are free of this problem. highdesertranger

 

[Goshawk]

Sounds like a ford design problem from that era. I knew a ford engineer who at that time was visiting a Toyota production line. He mentioned that ford tolerance measurements were a factor of ten less than Toyota. So it something had to be 10.1 inches in a ford, plus or minus .1 inches. In a Toyota they would be 10.01 plus or minus .01 inches. Ford was trying to change all there contractor suppliers to tight tolerance