View Full Version : Compression Test!! Help!
I just ran a compression test this afternoon since I found oil and coolant in cylinder 6 and just coolant in cylinder 5. All cylinders read 180-200 PSI so I am a little stumped :dunno After that I ran a reverse compression test through all cylinders. Air was escaping from cylinder 2 when the compression was placed on cylinder 4 :confused Please help!
-George
strad
09-12-2008, 12:07 AM
"Reverse compression test." What do you mean? I've heard of leak-down tests. . .
If you've got coolant in the cylinder, you have a blown head gasket or a cracked coolant passage. There's no other way it could have gotten there, unless you poured it in through the spark plug hole. The oil is another story -- could be oil that was on top of the spark plug and drained into the cylinder when you removed the plug, could be oil leaking past the valve guide, or could be oil getting past the head gasket from an oil passage.
bjh102
09-12-2008, 12:30 AM
head gasket. but the cylinder 2 and 4 thing is weird. change the head gasket shoudl be good. and get the head resurfaced.
Reverse compression is introducing air into each cylinder as they should hold pressure if both sets of valves for intake and exhaust are closed. Each cylinder should build up pressure or run air through the exhaust or back out through the intake. In my case, rather than build up pressure in cylinder 2, the air escaped out through cylinder 4. This lets me know that the head gasket isn't sealing off properly. I'm curious as to how the spark plug holes for 5 and 6 filled with coolant and oil specifically? I understand the gasket must be leaking from a coolant passage way, but directly to the spark plug holes?
bjh102
09-12-2008, 01:51 AM
well pistons 5 and 6 could be all the way up in the stroke and might of put the oil and coolant is just pushed up into the hole. it sounds like either your head gasket is leaking or that and your head is warped. no matter that the problem your going to have to pull the head off.
Yeah I'm working on it now...probably going to place the gasket and head bolt order tomorrow along with removing the head. The head shouldn't be warped as it was perfectly fine prior to removing, painting, and reinstalling it. Then again, anything is possible :shifty Thanks for the responses fellas.
strad
09-12-2008, 09:29 AM
Ahh, thanks for that clarification re: reverse compression.
The spark plug holes would fill with oil if the valve cover gasket (the little round one that surrounds the hole) has failed. You would very likely see the oil before you removed the plug though, since it would be pooled on top.
The coolant down the hole was a joke.
I would encourage you to check that head out very thoroughly for cracks. Inline six BMWs run hot on cyls five and six and have cracked the heads there on more than one occasion. Better to check before you bolt it all together!
drtweak1992325i
09-12-2008, 09:34 AM
So what is reverse compression test to you is leak down test for us lol. but they are the same...
Right now i'm redoing my headgasket, new head and valves. Getting head today FINALLY! guy forgot to ship it after labor day and didnt get it shipped till last friday. Got my cams out using the pelican DIY. From what my dad said it wasnt hard just teadious.
And if you are mechanicly inclined. Then a head job is a peice of cake really. Well at least for my non vanos. its just teadious, lots of stuff to take off, and remember where things go!
I'm sorry for not being more specific...the plug holes filled up on top of the plug for 5 and 6. Also, it astonishes me as to why each cylinder tested 180-200 PSI (meaning the chambers have compression) but failed the reverse compression test :dunno
So what is reverse compression test to you is leak down test for us lol. but they are the same...
Right now i'm redoing my headgasket, new head and valves. Getting head today FINALLY! guy forgot to ship it after labor day and didnt get it shipped till last friday. Got my cams out using the pelican DIY. From what my dad said it wasnt hard just teadious.
And if you are mechanicly inclined. Then a head job is a peice of cake really. Well at least for my non vanos. its just teadious, lots of stuff to take off, and remember where things go!
Yes, leak down test :) sorry for the confusion. Have not had the money to get new valves yet but do plan on it in the near future. +1 on the head gasket job with what your pops said. As long as you can remember where everything goes, then your good. Non-vanos are so easy to work with (see sig), especially the timing. Good luck with your project!
Montague
09-12-2008, 09:49 AM
So what is reverse compression test to you is leak down test for us lol. but they are the same...
Right now i'm redoing my headgasket, new head and valves. Getting head today FINALLY! guy forgot to ship it after labor day and didnt get it shipped till last friday. Got my cams out using the pelican DIY. From what my dad said it wasnt hard just teadious.
And if you are mechanicly inclined. Then a head job is a peice of cake really. Well at least for my non vanos. its just teadious, lots of stuff to take off, and remember where things go!
Oh, really :)? Finally? Looks like you've been waiting a while....
bjh102
09-12-2008, 09:50 AM
I'm sorry for not being more specific...the plug holes filled up on top of the plug for 5 and 6. Also, it astonishes me as to why each cylinder tested 180-200 PSI (meaning the chambers have compression) but failed the reverse compression test :dunno
maybe a crack farther down in the cylinders.....
BmotorMsportW
09-12-2008, 09:54 AM
it would be a good idea to get the cam locking tools and tdc pin before tackling this, it makes timing a sure thing, and trust me after all this work your not going to want a bent valve.
bjh102
09-12-2008, 10:26 AM
yes it does. but its a good time..... but seriously make sure there are no other cracks or anything. especially if your pulling it down already
axthrower
09-12-2008, 10:29 AM
For the cyl 4,2 thing sounds like you didnt have cyl 4 at TDC
drtweak1992325i
09-12-2008, 11:23 AM
Hey if you do plan on doing a head job. Let me know. I doubt we will use our cam locking tool and TDC pin and socket again. if you do it PM and let me know. might be able to sell it to you...
and yes i've been waiting 3 weeks now two of them are just for the head. i hope to get it done by next weekend. going to work on it alot this week. Going to be doing a few mods before this is done. Dad wants to put a drain and fill plug on the smaller one of the two fluid pans for my autotragic. That will make it easier to fill and drain. Dont have to take everything off! yay!
strad
09-12-2008, 11:57 AM
I'm sorry for not being more specific...the plug holes filled up on top of the plug for 5 and 6. Also, it astonishes me as to why each cylinder tested 180-200 PSI (meaning the chambers have compression) but failed the reverse compression test :dunno
Well then, if it was only oil, my hypothesis re: faulty spark plug hole gaskets would likely be correct for how the oil got to that location. You'll be replacing all that stuff in any case, because you can't put things back together properly without new gaskets all around. Good luck though. Sounds like you need it!
Hey if you do plan on doing a head job. Let me know. I doubt we will use our cam locking tool and TDC pin and socket again. if you do it PM and let me know. might be able to sell it to you...
and yes i've been waiting 3 weeks now two of them are just for the head. i hope to get it done by next weekend. going to work on it alot this week. Going to be doing a few mods before this is done. Dad wants to put a drain and fill plug on the smaller one of the two fluid pans for my autotragic. That will make it easier to fill and drain. Dont have to take everything off! yay!
Thanks but I do not need them ;) you could have easily timed your 92'er without those "special" tools. Make your money back by renting them out :buttrock
Out of curiosity, has anyone read that on the 92's when using the cam lock that you should space it out with something a certain way as BMW did this to smooth out the idle?
Well then, if it was only oil, my hypothesis re: faulty spark plug hole gaskets would likely be correct for how the oil got to that location. You'll be replacing all that stuff in any case, because you can't put things back together properly without new gaskets all around. Good luck though. Sounds like you need it!
Spark plug hole for cylinder 5 was filled with coolant and the one for cylinder 6 was a mix of oil and coolant. I figured that the valve cover gasket went bad (which was JUST put on about a week ago) which is why I was getting the leak into the spark plug holes. It was odd how 5 was only coolant and 6 was both. As you stated before, probably the oil and coolant passage ways on the head gasket leaking. Either way the head is coming off regardless as stated before, it just intrigues me to figure out why in the mean time. Thanks.
Tefal
09-12-2008, 08:50 PM
If the oil and coolant passage ways on the head gasket were leaking it wouldn't end up in the spark plug holes(top side of the plugs).
Any oil and water mix would show up on the dipstick or in the radiator/expansion tank
This is odd then because there was no oil in coolant nor was there any coolant in my oil. I have not ran the car very long at all though, maybe 25 mins total since the head gasket was replaced. We'll see. Thanks!
benemorius
09-12-2008, 09:49 PM
Does the engine not run right or did you just want to do a compression test out of curiosity? I wouldn't be so quick to replace that head gasket if I were you. I think it's a pretty safe bet that you didn't have cylinder 4 at tdc when you tested it. And as for the oil/coolant in cylinders 5 and 6, it just isn't possible for a blown head gasket to cause that. In fact, it isn't possible for coolant to get there at all. Sounds to me like the oil either came from spilling while filling or from the valve cover gasket, and the water came from either rain or a car/engine wash.
Does the engine not run right or did you just want to do a compression test out of curiosity? I wouldn't be so quick to replace that head gasket if I were you. I think it's a pretty safe bet that you didn't have cylinder 4 at tdc when you tested it. And as for the oil/coolant in cylinders 5 and 6, it just isn't possible for a blown head gasket to cause that. In fact, it isn't possible for coolant to get there at all. Sounds to me like the oil either came from spilling while filling or from the valve cover gasket, and the water came from either rain or a car/engine wash.
Well it did rain pretty harsh when we caught the after effects of hurricane Gustav. The reason I checked it out was because the car began idling rough and sputtering when I took her around the block, almost to the point of stalling. The problem was obviously the spark plug holes filled with liquids not allowing the car to fire right. I don't recall putting it at TDC at all :devillook that would allow the air to escape out of another cylinder?
Also, the engine ran strong up until this past week. I exaggerated running her for 25 mins total...more like an hour in total roughly, and up until now, she hasn't been idling rough or sputtering.
benemorius
09-12-2008, 11:09 PM
Yes you have to put each cylinder at tdc when you leakdown test it otherwise the air will just go through the open valves and come out the exhaust, intake, or any other cylinders depending on which valves are open on which cylinders.
I'd say start by doing a proper leakdown test. I'm guessing you'll get good results since compression checked out. After that, put it back together and see how it runs. Just make sure the spark plugs and coil boots stay nice and dry. You can probably find instructions for the leakdown test floating around here somewhere.
Alright, this is what I came up with as far as a leak down test goes...
3% to 5% - good racing engine
5% to 7% - good street engine
10% - weak
20% - shot
"Procedures
The first step is to ensure the engine is warm. Because we will be pumping air into the engine, leave all the spark plugs in except for the cylinder you're testing. As an example, let's start with a small-block Chevy, cylinder Number One. Yank the plug and turn the engine over until the piston is at top dead center (TDC). If you have balancer marks every 90 degrees, this will help. Now install the air-fitting adapter into the spark plug hole. You'll also need a breaker bar or ratchet and socket for the crank nut. Remember to double-check that your gauge reads zero before you start
There are also single-gauge leakdown testers. These gauges require you to zero the gauge with reference air (usually at 80 psi or below) before connecting the output line to the cylinder. Zero the gauge with the regulator. Once connected to the cylinder, the gauge will read out the actual cylinder leak rate.
The idea is to put air to the cylinder and then gently rock the piston around TDC to ensure the rings are seated. Keep in mind that cylinder pressure is used to help seal the rings to the cylinder bore, so you want to give them every opportunity to do so. Now record your leakdown percentage. It's really just that simple. Test the remaining cylinders in the same fashion and you're done.
Often, the cylinder pressure applied to the piston may turn the engine over. The key is to have the piston as close to TDC as you can so the crank, rod, and piston are all as vertical as possible. Once the rod journal has leverage on the crank on either side of TDC, the cylinder pressure combined with that leverage may force the piston down the bore. This is the reason for leaving the spark plugs in the engine." -Car Craft Magazine
In my case I did not have the dual guage leak down tester available but this should not alter my results in any way, correct? I understand why the cylinder tested must be at TDC now as well as all the spark plugs in except for the cylinder that you are testing. Hope this helps you guys as it did for me.
benemorius
09-13-2008, 01:35 AM
What sort of gauge do you have exactly? If it isn't a real leakdown tester you won't get the actual leakdown percentage, but it will still be useful to make sure that the air isn't going where it shouldn't. If you hear air coming out the exhaust, intake, radiator, or a different cylinder, then you have problems. You will always have a slight amount going into the crankcase (you can hear it coming out the oil cap) but excessive amounts are also bad. That's what the gauge is for determining.
Leaving the spark plugs in is up to you. If you leave them in, you won't hear it if the air is going from one cylinder to another. I prefer to remove them for that reason.
That article didn't seem to elaborate on tdc very much. You need to have the cylinder you're testing at tdc on the compression stroke. Since you can't tell which stroke it's coming up on without looking at the cams, it's best to start with #1 and proceed in the firing order. That would be 1-5-3-6-2-4. Use the timing marks on the crank pulley for #1. Stick a rod down the spark plug hole and watch it go up and down so you can tell when the cylinder is at the very top. After #1, move to #5. Rotating the crank clockwise, #5 will be on its compression stroke as it comes up. #3 will be coming up on compression after that, and so on. If you go out of order you might catch one as it's coming up on the exhaust stroke. If that happens, valves will be open and you'll get false results.
I do not have the percentage gauge, only the PSI gauge used to run the normal compression test. This isn't sufficient enough to run a leak down test? I understand the TDC reasoning and appreciate your thorough response on the subject as I am sure other readers in need of this info will be. Now, the leak down only tests for the cylinders, correct? The reason I am asking is because of the possibility of a leak in between a coolant and oil passage which would not show up through a leak down test, correct?
I assume the correct method would be to also run a coolant system pressure test. I have not seen any milky mixture on the dip stick, oil cap, or inside the expansion tank...however, the oil floating around in the head seemed to be somewhat watered down :dunno Hopefully the head gasket is alright as it would cost me roughly $100 for head bolts, new gasket, and oil. Thanks for the support!
benemorius
09-13-2008, 09:41 AM
I'm not clear on how that gauge fits in when you hook up your compressor and everything, but the accuracy of it with regard to leakdown percentage would depend on what exactly lies between that gauge and the gauge on your compressor. That's not an exact science, so if I understand you correctly then the answer is pretty much no.
If you have a leak directly between an oil and coolant passage, the leakdown test won't show it. As long as there's no water in the oil or the other way around, I wouldn't worry about it. I'm not sure where you said you may have seen watery oil, though. Do you mean in the spark plug holes or actually in the head. If it was in the spark plug holes, forget about it. They more than likely arrived there independantly.
drtweak1992325i
09-13-2008, 01:17 PM
about doing a compression test at TDC you dont need it at TDC...Dont know what hes talking about. For a compression test you just start the car up and let it crank a few times untill the pressure stops going up. And for a leak down you'd want the cylinder at the very bottom so that every part where air can excape would so you can find the prob...
now as for the oil and coolant...First i'd make sure that the so called coolant isnt just water as someone pointed it that it could be, and i had oil in half of my spark plugs a while back and found out my valve cover gasket it bad. Luckly we had a new one laying around lol.
Now did you change the 2 that go on the spark plugs or just the one around the edge?
paniolo
09-13-2008, 01:44 PM
about doing a compression test at TDC you dont need it at TDC...
The reference to TDC was regarding the leak down test, not compression
And for a leak down you'd want the cylinder at the very bottom so that every part where air can excape would so you can find the prob...
When you do a leak down you want the cyl closed up so you can find where it is leaking. That is why you want to perform it at TDC on the compression stroke as mentioned above. At the very bottom of the stroke some valves will be opening and is not what you want for a leakdown.
My bet is the OP head gasket is fine, the oil in the plug hole is from a bad valve cover gasket and any water from an external source.
Each piston being at TDC when tested assures that both exhaust and intake valves are closed. The purpose is to have pressure built up to see if it creeps through another cylinder which indicates a bad HG. If it is not at TDC, another cylinder's valves may be open, giving off an inaccurate reading since the air could escape from there.
We were discussing the leak down...for a regular compression test you are right, the cylinders do not need to be at TDC.
Tefal
09-13-2008, 06:53 PM
Each piston being at TDC when tested assures that both exhaust and intake valves are closed. The purpose is to have pressure built up to see if it creeps through another cylinder which indicates a bad HG. If it is not at TDC, another cylinder's valves may be open, giving off an inaccurate reading since the air could escape from there.And...........
When at TDC, If air escapes into the inlet manifold then you have a inlet valve problem,
Air out the exhaust indicates a exhaust valve problem,
Bubbles in the coolant indicate a major headgasket failure,
Air out of another plug hole indicates headgasket failure between two cylinders
Air out the dipstick or a engine breather indicate a hole in the piston/melted piston, broken rings......
There can be some other instances but I'm not getting into that.
Tefal
09-13-2008, 06:55 PM
Well it did rain pretty harsh when we caught the after effects of hurricane Gustav. The reason I checked it out was because the car began idling rough and sputtering when I took her around the block, almost to the point of stalling. The problem was obviously the spark plug holes filled with liquids not allowing the car to fire right. I don't recall putting it at TDC at all :devillook that would allow the air to escape out of another cylinder?I would check the DME housing out, it's probably flooded, common problem, especially after heavy rain
The DME is fine and dry...
Sigh this is getting to be a headache, especially for my wallet. It was pretty warm outside today so I decided to take a look at the car. Well, at about running temp I held her to around 3.5k and white smoke began to come out. Not in cloud fulls but enough to realize something is wrong. Also, whenever I held the throttle down she started spitting out what seemed to be lightly carbonated water (I am currently using water as coolant until this is sorted).
The car shudders very violently both in gear and out, but is worse when under load in gear. HELP!
PS. At idle the car runs pretty steady. Only under throttle does it begin to shudder.
bjh102
10-06-2008, 01:05 AM
it sounds like a leaky head gasket like i said earlier. just try that and get the head ground flat again then try that.
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