over 200k miles compresion test?

[Goshawk]

If you are considering buying a vehicle with over 200,000 miles on it; would you not go get a compression or leak down test on it to make sure the engine does not have issues?  Before you buy it?  Many think they are getting a bargain when finding a vehicle during their search.  But it becomes no bargain if it has to have major engine work done on it.  At least with this test done by a good mechanic you can say that it will be a drivable vehicle.


http://www.lcengineering.com/LCTechPages/gentech47.html

 

[29chico]

A compression or leakdown test is always a good idea.

However I have never done so when buying a used vehicle.  For starters, a gas rig from the mid '90's on up, when fuel injection systems got really good, there should be no or very very little carbon black in the tailpipe.  Then I do my own engine test:

This requires a long steep section of road where you can get up to highway speeds, little or no traffic is a plus.

Get the vehicle up to full operating temp.  Drive to the top of the grade.  Get going down the grade as fast as you deem prudent in whatever gear is direct drive (1 to 1), so overdrive off or 4th instead or 5th gear for example.  Make sure that you have a good line of sight on the outlet of the tailpipe in the mirror, or bring a helper along to do so.  When you are at your max speed on the steepest part of the hill take your foot off the accelerator as long as safe.  The longer in decel mode, the better. Don't go below 30mph or so before flooring the accelerator.  If the exhaust does not belch out any whitish smoke at that point, the engine is most likely in good shape as far as compression goes.

The above test has worked great for me many times.  I still strongly suggest getting a pro to check out a prospective used vehicle purchase unless you are highly skilled yourself.

 

[highdesertranger]

here's a tip or warning, however you want to take it. synthetic oil does not smoke(no blue smoke), so unscrupulous sellers put syn oil into smokers before selling. old used car dealer trick. highdesertranger

 

[wagoneer]

an old friend bought a BMW M3 and we took a compression test it was above normal on all 4 cylinders scratching our heads, it was low miles but above stock was a bit strange non the less upon thinking about this we came upon the conclusion that this guy never "really" drove it the way it was meant to be driven, took it out to the raceway pumped some high octane and put the foot down hard. Black smoke for a while and then it calmed down. Well this rich kid drove at posted speeds and the carbon buildup was raising the compression. Tested again and they were all spot on. Not that a van is a BMW M3 but it helps to think outside the box for a conclusion. ( what was that about?lol) OK OK off topic.

 

[Goshawk]

Actually that right on topic wagoneer. It's a good example of how to misinterpret compression test readings.

 

[29chico]

here's a tip or warning,  however you want to take it.  synthetic oil does not smoke(no blue smoke),  so unscrupulous sellers put syn oil into smokers before selling.  old used car dealer trick.  highdesertranger

Good point. 

You have got me wondering if group III motor oils, which are commonly called synthetic, will smoke in a worn engine like a group II would.  I have known for a long time that group IV & V oils are smoke free.  Any input on that?

 

[idn88]

A compression test is never a bad idea, however if it has really bad compression the OBDII will usually throw a code. However you would need to check for codes and also that all the readiness monitors are all set - meaning the owner hasn't simply just reset the codes. A good ODB II tester will show this, or your mechanic should know how.

However, usually at 200K the engine is fine but everything else is worn out. Most people will change their oil every 3000, but never change Transmission or differential fluids, or service wheel bearings, U-joints, etc, suspension and steering components, etc.

 

[gojo]

If you are considering buying a vehicle with over 200,000 miles on it; would you not go get a compression or leak down test on it to make sure the engine does not have issues?  Before you buy it?  Many think they are getting a bargain when finding a vehicle during their search.  But it becomes no bargain if it has to have major engine work done on it.  At least with this test done by a good mechanic you can say that it will be a drivable vehicle.


http://www.lcengineering.com/LCTechPages/gentech47.html

To be honest, I wouldn't buy an gasoline engine with 200,000 miles on it. Some do make it up to 300,000 miles, very few. You'll have other things to worry about and they cost a lot money for repairs too. Like for instance Front end suspension, such as ball joints, steering linkages, complete brake job, transmission, rear diff., bearings, sensors, and this is only a few.
In my own opinion, I won't buy any gasoline vehicle with over 120,000 miles on it.
I wouldn't just look at the engine's mileage.
Now on the older diesel engines, I would buy one with higher mileage. I've noticed they get a bad name here. Guess because it's something different.
But they're not all that bad.

 

[gojo]

Good point. 

You have got me wondering if group III motor oils, which are commonly called synthetic, will smoke in a worn engine like a group II would.  I have known for a long time that group IV & V oils are smoke free.  Any input on that?

When engine is warm up and running, remove oil filler cap and you'll see if it has blow-by.

 

[gojo]

here's a tip or warning,  however you want to take it.  synthetic oil does not smoke(no blue smoke),  so unscrupulous sellers put syn oil into smokers before selling.  old used car dealer trick.  highdesertranger

 Then this one would fool me on bad valve guides. Usually if you have bad valve guides, engine will smoke when cool down on crank ups.

 

[idn88]

The whole xxxx mileage thing is really a misrepresentation of engine component wear. If I drove a engine at highway speed continually for 200K miles you would see hardly any internal wear. You might need timing chains, but that would be about it.

If I drove the same thing for 100K in start stop short trip city driving, it might be shot.

They really should implement an hour meter like they do on commercial vehicles.

The overall condition of the rest of the vehicle will likely tell you as much about engine wear as anything. You can also take a oil sample and get it evaluated, but that takes a couple weeks.

 

[SternWake]

The driving habits of the previous owner is a huge factor.


I had a GF once whose driving made me cringe.  It was as if she had to be accelerating hard or braking hard, and holding a steady speed was to be avoided at all costs.  She would accelerate faster than the car in front of her, and have to hit the brakes, like 5 times upto 45 MPH.

At 40K miles on her car she had bought new, the right side of her brake pedal had been worn down through the rubber to metal below. and the rubber was starting to pull off the pedal on that side, and looking brand new 4 inches away.

When she'd drive she would be lucky to get 12mpg from a 4 banger around town driving, and 18 highway.  I was able to get over 30 when i'd drive it on the highway.

Whomever bought her car afterward would have been buying a vehicle seriously abused for its mileage.

So, check the condition of the brake pedal.  Clues as to how it was driven lie there.

 

[Goshawk]

So quick recap. Check to see if timing belt has been changed. Or even if it has a belt or a chain for timing and if the engine is free wheeling (valves will not hit if the timing belt breaks). And check the brake pedal for wear. --- plus the compression check.

If I am spending over $5000 on a vehicle this would be cheap insurance that it's not going to have engine problems.

 

[ascii_man]

A compression gauge costs about $30 and there are several YouTube videos about how to do it (see a Haynes or other manual for vehicle-specific details); you just disconnect power from the spark plugs, insert it in place of the spark plug, and crank the engine for a few seconds.

 

[Goshawk]

One mobile mechanic told me he does not do compression test. Guess the liability of pulling the spark plugs and then putting them back after a test is too much? Sounds silly but guess I am not using that mechanic. Anyone who calls themselves a mechanic must be able to do a compression test. It's not that hard.

 

[idn88]

One mobile mechanic told me he does not do compression test. Guess the liability of pulling the spark plugs and then putting them back after a test is too much?  Sounds silly but guess I am not using that mechanic. Anyone who calls themselves a mechanic must be able to do a compression test. It's not that hard.

Depending on the engine, I don't blame him one iota.

5.4L ford - plugs might be seized in.  Each one costs about 400 bucks dealer price to fix the stripped threads x 8.

A lot of newer engines require the intake manifold to come out.  Can cause future air leak problems.

A lot of newer engines with aluminum heads, if it has high miles and the plugs have never been out you have a legitimate chance of wrecking the head.

Of course, all of these would be good to know about a used car before you buy it as well, however if I were a mobile mechanic I would probably also think the risk isn't worth the couple hundred I am going to make on the compression test.  If he damages anything above, he is likely going to be sued by the vehicle's owner, and there is no way he is going to get you to pay for it when you don't own the thing yet.  Sounds like the risk is all his.

 

[gojo]

Depending on the engine, I don't blame him one iota.

5.4L ford - plugs might be seized in.  Each one costs about 400 bucks dealer price to fix the stripped threads x 8.

A lot of newer engines require the intake manifold to come out.  Can cause future air leak problems.

A lot of newer engines with aluminum heads, if it has high miles and the plugs have never been out you have a legitimate chance of wrecking the head.

Of course, all of these would be good to know about a used car before you buy it as well, however if I were a mobile mechanic I would probably also think the risk isn't worth the couple hundred I am going to make on the compression test.  If he damages anything above, he is likely going to be sued by the vehicle's owner, and there is no way he is going to get you to pay for it when you don't own the thing yet.  Sounds like the risk is all his.

You're right, you hit the nail right on the center of the head. Late 90s on fords aluminum heads, they only have 5 threads and it don't take much strength to strip them. I use a inch pound torque wrench to install spark plugs on these engines. Never had a problem.....

 

[Goshawk]

So what you are saying is don't buy a ford? Or any vehicle with aluminum head? Again is that a mechanic you can trust? If they can't handle pulling spark plugs? Then they can at least say it's aluminum head and there is a high risk for major problems, please wave your liability.

 

[gojo]

Go  to google search and enter ford 4.6 and 5.4 engines blowing spark plugs. That is a ford problem on earlier model trucks.

 

[gojo]

Here is a torque sheet. I will repeat, I have never had a problem with spark plugs on ford aluminum heads because I use a inch pound torque wrench.
http://www.torkspec.com/index.aspx