: A question for the more experienced N* gear-heads on site. Gasket or rings?
08-09-12, 10:46 AM
I've got a customer with a 2000 DTS sitting at 132K. He keeps the car well maintained and it has never been overheated. He dropped it off yesterday morning with a rough idle that turned out to be a cylinder 1 misfire. The misfire was only present at idle and went away with throttle. I checked for vacuum leaks and found none. I swapped the fuel injector with another cylinder but had no change. So I did a compression check and found number one had only 85 PSI at WOT cranking, while the adjacent cylinder has 190 PSI. I added some motor oil and the pressure jumped to 130 for a few tests so it's not the valve train, and there are no other reasons to suspect valve train. I was already assuming the headbolts had pulled out but I did a combustion leak detector (block check) test and trying as hard as I could I can not get any indication of combustion gas in the cooling system. I even power stalled the engine against the brakes at 1500 RPM for a few minutes, the engine still doesn't run hot or out gas from the coolant reservoir. So at this point I wonder could it be the ring cleaning procedure I read about in the sticky on the N* forum of this site? I guess what I'm asking is how often do these rings stick and what are any common secondary indicators of this? The top of the piston looks to have a good layer of carbon on it and the previous tune up was done with standard copper plugs and they are about gone at 0.059" even though they have only been in for about a year and standard mileage for that amount of time. Otherwise the engine runs great.
Also the customer stopped in yesterday afternoon to check on it and I told him what I had found so far and told him a shot from the hip quote of approximately $2,500 to replace both gaskets and install Norm's inserts in the car. Does this sound right? In any case I don't want to replace gaskets for a no change result.
08-09-12, 10:52 AM
Also he is a retired coroner, WOT is rare and short lived on this car at most.
08-09-12, 10:54 AM
In a sedentary Northstar, stuck piston rings are somewhat common. They're low tension rings and like to be 'exercised' once in a while. You might get away with GM's piston cleaning procedure - chemical cylinder soak, vacuum it out, run engine, change oil and filter right away. Google "cadillac forums northstar piston cleaning procedure" or something similar, preceded by "cadillac forums" - the info is in here somewhere.
Go up to the Cadillac Technical Archive in the black top bar ^^^ and read the article "Occasional full throttle operation is good ........." - there's more insight there.
His engine takes an AC Delco #41-987 Platinum plug, pregapped to .050". They're good for at least 100,000.
The kicker with the $2500 quote is that, once you get into the crankcase separation and piston pulling business, parts and labor time get expensive, so I would think that $2500 for a complete overhaul is very low - OK for top overhaul, but you found out it's rings, not valves ................
08-09-12, 11:51 AM
Thanks Sub. He came back by just after I posted and I told him where I was at with it. He said that if the ring cleaning procedure is worth a shot to go ahead and try it so I will do that next. He also said he's about to go out of town for two weeks so that would give me enough time to repair the engine if need be. The quote was for doing an in car head gasket job only. If it needs rings I may persue other options such as a long block, but I'll cross that bridge when I get there. I had based the price on posts I've read by established N* techs on this forum. I had read the sticky already and actually performed it on a old Sunbird that my wife uses to deliver mail with a good result. It's still running and the one weak cylinder came back enough to work for now. Based on what you've said, and I have already judged your judgment highly, is that it's worth a go and could be the issue. I'll let you know how it turns out.
I guess what I'm asking is how often do these rings stick and what are any common secondary indicators of this?
Secondary indicators are excessive oil consumption. Have you taken it out for a couple of good WOT runs? That just might do the trick.
08-09-12, 01:09 PM
Ranger I did a couple of short WOT runs yesterday to check for misfire under load before I started digging into the other things. Not enough really to get the manifolds red but I do have it back together so I could take it to lunch and perhaps go to the nearest safe stretch to blow it out.
Can't hurt. Seems like the more you beat on them, the more they like it and the better they run. I know it helped the oil consumption on my '97 once I learned about it and gave it a monthly dose.
08-09-12, 09:39 PM
I agree. I wail on mine, being a leadfooted young man, and she doesn't noticealby consume oil during my 3,000 mile oil change intervals.
08-10-12, 03:52 PM
UPDATE: I did the chemical (OTC Injector Kleen) soak yesterday and it ran smooth hot then drove the car home (16 miles) but didn't get very many WOT runs in due to traffic. In my drive it was smooth. Started this morning with the miss but was smooth by the time I got to work. Today I did two soaks in a row with Mopar EGR system cleaner which is a very powerful detergent you cut with water and it really softens carbon up. I did a compression check after the second and found about 50 psi but I figured it may just be the gunk all packed in so I buttoned it up and went on a 20+ mile drive with many WOT runs through the first three gears. It was smooth when I returned but I did pick up two misses in a row waiting at the light up the street. Pulled the plug and did a compression check, 175 PSI!!. It's working. But my test hose got hot and is now stuck in the head waiting for it to cool down. When I get the hose out I'm going to give it another scope inspection and may try another chemical soak. I'm thinking I should do all of them at once to finish it off and prevent the other cylinders from doing the same thing any time soon.
08-10-12, 04:38 PM
:D That is a good reason to do frequent and spirited WOT runs!
It sounds strange when someone has a problem like that or oil consumption and we tell them to take it out and "drive it like you stole it" and beat the living daylights out of it, but it works. I'm sure more than one person has gone away thinking "these guys are !@#$%$^** crazy".
08-10-12, 11:14 PM
Some people never, and I mean never go past about 15% throttle. I'll get into a vehicle and give it some pedal to get onto the road ahead of traffic and it's like somebody knocked over a book-case full of nick-nacks watching all kinds of crap fall off the dash or out of visors and whatever else. I don't mean WOT I mean what I consider normal acceleration. Then there's the women who would bring in a Suburban at 125K and say the transmission is acting up and it won't shift right or hangs up. So I'll go out and sure enough it won't shift out of second. But not because the transmission is stuck but because the fuel filter is so clogged that the engine can only make about 20 HP, after that it runs out of fuel. They don't notice until it prevents them from reaching gear changes at part throttle cruise. Never mind it wouldn't have accepted a half throttle pedal a few months ago much less a WOT event in the last year. The funniest ones are the looks you get from people who go on a test drive with you and don't know how to operate a vehicle at WOT. So I floor it to check, demonstrate, etc. and they look over all confused like "How are you doing that, is that hurting it?" "I didn't know it could do that!" Hell, just floor it. What's there to know, fear, or find out.
Did I mention that I get impatient in traffic? LOL
Oh BTW the hose is still stuck in the head.
09-02-12, 06:50 PM
Conclusion: The ring cleaning procedure brought this Caddy back to life and it's been back in use for a couple of weeks without any issues. The owner was on a weeks vacation when I had it so after finding success in bringing compression back to #1 all of the other needed repairs and maintenance were done to bring the car up to keeper status for the foreseeable future. I finished the ring cleaning by performing it a second time in all eight cylinders with the actual GM Piston and Ring Cleaning chemical. It took two cans at $24 each wholesale. I followed the prescribed procedure then afterwards the more it was driven the better it was. By the time all of the other repairs were done it was running fine.
This is something to keep in mind when someone develops an idle miss that is caused by low compression when no head gasket sealing issues are evident and the valve train is also good.
09-12-12, 11:57 AM
Conclusion: It took two cans at $24 each wholesale. I followed the prescribed procedure then afterwards the more it was driven the better it was. By the time all of the other repairs were done it was running fine.
Good Lord. That much at Wholesale? But if it works... Sounds like it's easier and cheaper to floor it from time to time.
09-12-12, 12:53 PM
Yeah but if you're not careful with the cooling system that causes blown head gaskets. I blew my head gaskets at over 114 MPH passing a train of slow traffic following a farm trailer in deep east Texas, a darn top of the tank leaky radiator got me on a long trip- LOL. Not to mention the first time I overheated it when the 130K water pump belt tensioner couldn't handle frequent WOT that I started exposing it to and so it fell apart when I started it one cold morning and went back inside to let it warm up, it did :).
Vernon I'd bet your HGs where ready to go anyway. Running WOT doesn't cause them to fail. The Northstar was run at WOT for 300 hours (12.5 days) straight during the testing phase.
09-12-12, 04:58 PM
Ranger, I let it get to low on coolant prior to doing WOT, that was what I was trying to say. If you're going to run WOT you had better make sure your cooling system is in tip top shape. My temperature gauge was normal when I started my pass and after about 4-5 cars and a truck/trailer I pulled in just as I heard the instrument cluster make a ding sound and it was pegged to the cross-hatches. It happened that quick. Belt drives with over 100K should just be replaced, esp. if you are considering WOT more than a quarter mile from your house.
OK, gotcha. Yeah at WOT the water pump really speeds up and sucks down the surge tank. If you are low, it'll start sucking air and that ain't good, especially at WOT and high RPMs.