My Compression Test Results

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82vdub
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My Compression Test Results

Post by 82vdub »

I did a compression test today. I'm looking for some feedback on where to go from here. I did the test a couple ways. All numbers below are from (top down) cylinders 1, 2, 3, and 4. First test I cranked the engine for 5 compression strokes, stopped and read the number. Then, I continued cranking until the gauge would not read any higher. Then, I let the engine sit for 6 minutes, re-read the gauge to see if there's any leakdown. Results are below.

My engine, when cold, is extremely hard to start. Been that way for years, and it's slowly getting worse. It will pop on a cylinder or two, then after it's running for a bit, the other cylinders will finally run. After letting the car sit for 9 hours on a day that's 50 degrees out, it's pretty hard to start and worse when it sits overnight.

Compression test with 5 compression strokes:
335
320
325
320

after 5 stroke compression test, max compression seen:
495
460
475
458

after letting the engine sit for 6 minutes:
495
460
470 (note 5 psi change)
455 (note slight change)

I then started over and performed a test to determine how many compression stroked it took for the gauge to stop going higher. These numbers are:

15
13
14
16

When the head was last off about 70,000 miles ago, I remember being amazed that there were still hone marks in the cylinder walls. The car really doesn't use any oil, that I know of. It leaks some oil from the front seal and around the oil pan, but I can probably get 3000 miles to a quart or so (haven't really paid attention to it). This spring, new timing belt, rebuilt IP and I checked the glow plugs and replaced a few.

I just did the simple glow plug test - turn the key on and run and look in the injector holes. I may have found my problem, or part of it. The new Autolite glow plugs that I installed this spring didn't glow (31 and #2 cyl), and the good used plug that's in #3 started to glow before the relay kicked out. The good used plug in #4 cylinder glowed pretty nicely red. I'm going to get a set of datatems (spelling??) and install those as soon as I can.

I'm going to measure my battery cables today as well. This car cranks over slower than my Jetta. I'll report those shortly.

Any ideas on what to further test for better cold weather starting?
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surfcam
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Post by surfcam »

I think starter, battery, and cables is good thing to go over this time of year. I have five starters kicking around I lube one up, check it out and just change it out. If I suspect the starts beginning to drag. You want to check the bearing in the bell housing as well and change it if it has any wear. Lube it also. A lot of auto parts store will check the starter for free so thats another thing to do.
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Post by VanagonExpress »

Looks good to me...
but then again, I usually am good for 10 strokes....( :oops: :oops: :oops: :oops: )

You KNOW someone was going to say that....so I did....THERE! :lol:
Vincent Waldon
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Post by Vincent Waldon »

I think your compression numbers are fine... in fact, great.

Assuming your cranking speed is fine I'd be inclined to make sure all 4 glow plugs are in perfect shape and confirm they are getting a solid 10V.... Bosch Duraterms are the way to go for sure.

Timing can also make an otherwise good engine hard to start in the cold... make sure you're at at least 0.90mm with the cold start knob pushed all the way in.
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Post by tawney »

This car cranks over slower than my Jetta.
If that's the case, I agree with Surfcam: take the starter apart: clean, grease the bearings and moving parts, grease the bushing in the bellhousing, and put it back on. It has made a huge difference for me in rotation speed while cranking, and ease of starting is so much better.

A well lubricated starter and new glow plugs will make it start like new, assuming your timing is correct and the cold start advance is working.

Your compression is great! Not sure about your improvised 'leak-down' test results, though. I think what you've got there is simply the compression gauge holding the pressure for you.

Steve
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82vdub
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Post by 82vdub »

Not sure about your improvised 'leak-down' test results, though. I think what you've got there is simply the compression gauge holding the pressure for you.
Well, that's a great thing for me to check. Never thought of that. I set the car aside for now and will drive my Jetta for the next couple days. I ordered some Bosch Duratems from the local No Auto Parts Available store (that's NAPA for those that wonder). They will be here Monday or Tuesday and I will try to put the car back together again in the dark.

I did remove all 4 glow plugs and tested them individually. The two "new" (as of spring) glow plugs didn't glow or get warm, the other two glowed nicely when I tested them. I believe that the two Bosch glow plugs that worked are original to the car. Only a ba-zillion starts on them and they work better than the 6 month old Autolites. I've never liked Autolite or Champion spark plugs before, and maybe not much else now.

On the starter bit, I've had the starter rebuilt before (many times) and changed out the bushing in the trans etc. No matter what I've done to the starter, it doesn't crank over as fast as my other diesels. The car has been in the family since new, but when my father had it, I don't remember how it cranked over. I didn't get around to checking the cable resistance yet. I will try that tomorrow.

I have to pull the engine out yet this fall to correct a couple things: replace leaky water pump, move flywheel 120 degrees so I can propertly time the engine (I don't know if this is the problem or not, as the hard starting issue has been there for years when it gets cold out), and change out motor mounts. I want to resolve this starting issue before I pull the motor, since I only want to pull it once and will fix the head or whatever when I pull it. Not interested in pulling the motor twice if I don't have to.
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libbybapa
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Post by libbybapa »

Why didn't you replace the leaky crank seal when you did the timing belt?

Your compression is terrific. As mentioned, cleaning and relubing the starter can make an absolutely huge difference in cranking speed, as can having heavy gauge, good condition battery cables and a good ground path. Make sure there aren't any corroded connections on the ground path. If the battery strap is mounted to the tranny mount, then make sure the connection between the mount and transmission is clean and bright.

Duraterms are great plugs.

If two plugs burned out, I would be concerned about the glow plug relay. I replaced one in a friend's Quantum today because it was clicking away intermittently. That's a great way to burn out the glow plugs.

If you are using an ohm meter to test your battery cables, the test will not be useful. I have heard that sometimes a cable will have very little resistance until a significant load is passed through it and then the resistance will increase dramatically. The ohm meter only passes a very small current and so does not give any useful information.

Your battery has lots of CCAs (like 750+) and is less than 2 years old?

I don't see why you would pull the engine. It would be easier to pull the transmission, even if you add in the work of changing the water pump. I don't understand why you think there is a problem with the head??? Did I miss something?

Andrew
Last edited by libbybapa on Sun Nov 11, 2007 10:19 am, edited 1 time in total.
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Post by Fatmobile »

Check the cables and connections by cranking for awhile then feeling them.
Hot spots are where the bad connections are.
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82vdub
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Post by 82vdub »

Why didn't you replace the leaky crank seal when you did the timing belt?
Couple thoughts:
It's not leaking much, just enough to cover the bottom of the car and make a slight neusance on the driveway. It's not leaking enough for me to lay on my back for hours experiementing with changing out the front seal.

I've done plenty of engine work to Chevy's and Fords, but I've never done anything inside the block of a VW - only head on up and exterior to the engine. So, I'm a little reluctant to just jump inside.
I don't see why you would pull the engine. It would be easier to pull the transmission, even if you add in the work of changing the water pump.
I've pulled a VW motor a couple times. Been years, but I do remember thinking last time that if I ever need to do anything to the transmission, it's so simple to pull the whole engine/trans combo that it would be so simple to pull them as one unit. I still think that today when I look at the engine. I'd doing the work by myself, so I can easily pull and place the engine by myself without needing help. I need to rotate the flywheel 120 degrees so I can time this motor, and also need to do the motor mounts. With work at both ends of the motor, I'll definately pull it. I can then work on it in the garage on a stand and it's easier than laying on my back trying to do it in the car. While it's out, I'll do the water pump and probably look at the front seal and resealing the oil pan.
I don't understand why you think there is a problem with the head
You didn't miss anything. I've been dealing with an engine that has been getting harder to start every fall (cold temps) for years. This spring I bit the bullet and had the IP rebuilt. Did the timing belt and checked the glow plugs at that time, new nozzles etc as well. This fall, same hard start problem. I don't know if I had/have a head problem, compression problem, cranking problem, or what. I did the compression test yesterday, but I don't see a problem in that department. So, since there doesn't seem to be any compression issues, there probably isn't any head issues and I'm not looking in that area at this time. I'm going to get the duraterms installed tomorrow or Tuesday and see how it starts with all new glow plugs. If it still starts hard, I will have to do more research and go from there.
If two plugs burned out, I would be concerned about the glow plug relay.
Why would you suspect the glow plug relay when 2 plugs are burned out? Am I missing the idea of how two plugs would burn out if a relay is bad? The general consensus is that Autolite glow plugs suck, and that's what was installed this spring and those are the two that are burned out. The two plugs that worked were either the original plugs to the car, or removed from a parts VW out back and tested (by the visual glow) when I did the service work this spring. The car has never had any electrical problems since new and has never burned out a fuse since I've owned it.
Your battery has lots of CCAs (like 750+) and is less than 2 years old?
Yes to both
Last edited by 82vdub on Sun Nov 11, 2007 6:06 pm, edited 1 time in total.
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libbybapa
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Post by libbybapa »

Once you have a crank holding tool (easy to make) swapping the front seal is quite easy, but does require the removal of the timing belt.

If you are also replacing engine mounts then it does make sense to pull the engine for the clutch.

There is no reason to suspect anything with regard to the head. Your compression results are great which shows the valves are doing their job well. The compression reading is always the result when the needle stops moving upward. Basically the engine is always producing that pressure, you are just pumping up the hose and fitting of the compression tester to match what the engine is always producing.

Glow plug relays will often fail to a situation where they turn the glow plugs on intermittently while driving. Very common. That situation results in plugs burning out. I'm not saying that IS a problem with your car, I'm just suggesting that it might be. You could easily rig up a light that would come on whenever the glow plugs were given current. That way, if the light ever came on when it shouldn't you would catch it prior to not being able to start the car. Certainly the suckage of Autolites would mean that if the relay was giving power when it shouldn't, they would be the first two to burn out resulting in hard starting. The relay clicking on would not affect the rest of the electrical system or any fuses.

Andrew
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Post by 82vdub »

I got the new glow plugs last night, installed them and got the engine all buttoned up and fired up. After it's initial startup, I ran it for 2 minutes to check for leaks. I shut it off and wanted to let it sit for a while to see how well it starts with cold temps. At 10:15, I went out and cranked it over. Without my foot on the gas, the car fired up, chugged a couple times and quit (probably upper 40's outside). I did the same thing again and the car stayed running and ran on all 4 cylinders after a matter of a second or two. It hasn't started like this (when it's cold out) for years, maybe even close to a decade. Normally this time of year, I've already switched out to the winter car as this one was always hard to start.

This morning it was 30 degrees F out. I started the car up (with foot slightly on the gas) and it fired right up and ran on all cylinders in a matter of a second or two. Boy, am I pleased to know that I don't have to get any further into the engine to fix the hard starting issue. Not too bad for an engine that has 1/3 million miles on it.

I'm going to dig into the slow starter issue. I'll start with swapping out some battery cables from a dead Rabbit sitting out back and see what that gets me.
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Post by crankpot »

Dont forget injectors. It takes a good injector for easy starts. Old worn units don't atomize well and the spray is hard to ignite.

Your engine will run qieter as well.

Bob
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82vdub
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Post by 82vdub »

Injectors were done in the spring, 10k miles ago. It does start great so far, but today is the first day I took it to work. I will find out how well it starts in 20 minutes after sitting all day outside. Tomorrow will be a better test, it's supposed to only get up to 40 tomorrow. I plan on pulling the motor and doing the flywheel, mounts, water pump etc on the weekend of the 24th and the bigger plan is to take the car to Denver over Christmas/New Years, if the wife doesn't resist taking this car.
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Post by bottleworks »

libbybapa wrote: If you are using an ohm meter to test your battery cables, the test will not be useful. I have heard that sometimes a cable will have very little resistance until a significant load is passed through it and then the resistance will increase dramatically. The ohm meter only passes a very small current and so does not give any useful information.
That's right. A voltage drop test needs to be done (when cranking) if you wish to test your battery cables correctly.
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Post by harry_the_face »

bottleworks
Can you describe a "Voltage Drop Test" to us Newbies :D
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