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Discussion Starter · #1 ·
I did another compression test before I tear in.

Cold 90-85-100-85
Cold w/gas to floor 70-80-90-60

Seems strange, no? Only thing I could figure is my gauge isn't connecting into the socket cleanly. The #4 socket it barely can thread in, but in the other 3, it goes at least a full turn. Not sure what to do about it to get a good reading, but I've done the test before, and found #1 and #2 to be low.

The shop I had it at told me it was low in 2 cylinders as well. So I think I'm safe in assuming the head gasket needs replaced, minimally.

2 other issues- if the catalytic converter is badly clogged, could the car run cool, but then heat up when it is idling? However, I have had a car with a clogged cat, and that one began topping out at 50mph on the interstate. However, my mx6 has no problem with speed.
Also, when I remove the head to send off to be planed and tested, I assume I need to remove all the components inside. Correct? Then I'd be basically rebuilding the head.

Should I just buy new parts, or should the 150,000 mile parts I have be reinstalled? Would the cost be that much more to buy new internal parts for the head?
 
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You really should perform a leakdown test first to see if your losing the compression through your valves, rings, or headgasket.

If you do pull the head, you don't need to remove the valves, just pull off the front and rear housings, rocker arm shafts,and cam.
 

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can i fit 2 of those to be really safe?

*climbs under desk to ride out the storm*
 

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Discussion Starter · #5 ·
Ok...after reading up on other sites (search on here brings up nothing) about leakdown tests, I just may do that too. However, that involves taking the car to a shop, as I don't have an air compressor.

My other option then, is to replace all the possible problem parts. Is that too ambitious? Valves, rings, head gasket...do em all at once? Assuming the head isn't cracked, how much should that be in parts?

I like my MX-6. It's in good shape inside, the engine was running great, and there's only minor issues otherwise. If I can do it, I want the car to last.

Car's in the garage, heat shields removed. All the bolts to the exhaust manifold are removed...thinking of my next move.
 
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Somewhere around here is my writeup to removing the head, but the search function is borked or something and it wont bring it up.
 

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My advice is to make sure you have a mazda factory workshop manual if you're going to be doing head work. If this is your first time doing this and you don't have this book as a reference you are probably going to mess it up.

Also, if you want to seriously replace everything inside the cylinder head you're talking a lot of money. I would recommend you find a shop that will rebuild the entire cylinder head for you. There are a few places that you can send your old cylinder head as core credit and then get a rebuilt one sent to you for a few hundred bucks. This is what I would do if I wanted to replace the head and internals.

BTW, the fastners holding the exhaust manifold onto the cylinder head are studs and nuts, not bolts. If they came out in one piece (i.e. a nut frozen/rusted to a stud so it looks like a bolt) you're going to need to replace that hardware.

Oh, and install the 2-stage thermostat :D That picture you took of your gauge cluster on the highway is consistent with having a thermostat rated "too cold" for this engine. The temp needle is supposed to sit just to the left of dead center. The reason yours sat quite a bit to the left is because the 180 degree thermostat sets the engine operating temp at about 8-10 degrees lower than it should be (around 188-190C with the 2-stage), so this would make sense. Also, the transient effect of the "cold shock" given by a single stage to a hot aluminum/cast iron (as discussed before) engine is to be noted. This may or may not have led to your head gasket failure.
 

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Well, it is possible that you are not getting the compression tester installed good enough to get accurate readings. My 89 PGT gets about 155 on all four (within 2 PSI). Of course I bought it new and it has been well taken care of its whole life!

On the other hand 150k is enough to wear out the rings which is what it sounds like assuming the compression guage is making good connection. I would go ahead and put new piston rings in while you have the head off. I just did the same job on my 89PGL last weekend. It took most of two days. But a lot of that time was spent cleaning parts and scraping old gaskets off.

After you pull the exhaust manifold off, just take the intake manifold loose and it will move back from the head about two inches, so you can just leave it in the car and pull the head out. Again, leave the exhaust manifold in the car just pull it away from the head enough to get clearance. You will need a 27 mm wrench or big adjustable to get the EGR tube nut loose at the manifold. It will need to come out of the manifold to move the two mainfolds away from the head. Then just take the timing belt off and pull out the distributor and the easy part is over!!
 

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Discussion Starter · #9 ·
Thanks, that should be helpful.

Where exactly are the rings?

I guess I should be looking this stuff up in my repair manual. :)
 

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Illswyn said:
Thanks, that should be helpful.

Where exactly are the rings?

I guess I should be looking this stuff up in my repair manual. :)
....so you're going to rebuild your cylinder head, and you don't even know what or where your piston rings are?? Sounds like it's time for some reading and learning before you tackle this project. I recommend going here first: http://auto.howstuffworks.com/engine.htm
 

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Illswyn said:
Where exactly are the rings?
Once the head has been removed, you still won't see them. And if you replace every single part on the head, you won't have replaced the rings.

And you might STILL have a compression problem. So pay close attention when FlySwat says:

FlySwat said:
You really should perform a leakdown test first
Wouldn't it be a bitch if Illswyn spent 5 or 6 hundred bux and was still down on compression?

Hopefully, he wouldn't blame the machinery.
 

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Discussion Starter · #12 · (Edited)
Sorry magik8, I wasn't born with automotive knowledge. I didn't grow up working on cars. None of my family works on cars. Although I've heard one tooled around with some in the 70's, even he's mellowed out and has a Hyundai now.

I've been to the howstuffworks.com page plenty. So then, I assume I need to remove the pistons to get to the rings?

And as for the exhaust manifold bolts/studs/nuts/screws/nails, etc...yes I know...one of my studs is broken. Been that way since I bought it. Another of them busted a while back, can't help it. I might replace it, might not.
 

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I just wanted to make sure you know what you're getting into. Rebuilding the head is a pretty big job, and is not something a "beginner" usually tackles. There are lots of parts that have to be assembled in a certain way or you can have catastrophic engine damage. Good luck, and make sure you have a good manual to glean information from. Be sure to follow torque specs very carefully as they are critical to these moving parts.

Illswyn said:
And as for the exhaust manifold bolts/studs/nuts/screws/nails, etc...yes I know...one of my studs is broken. Been that way since I bought it. Another of them busted a while back, can't help it. I might replace it, might not.
Well you can easily replace them or have them replaced if you're having the head rebuilt somewhere. Definitely have that done if the head is going to be out of the car; it is much easier that way.
 

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head rebuild requires detailed skills

Illswyn said:

My other option then, is to replace all the possible problem parts. Is that too ambitious?
Car's in the garage, heat shields removed. All the bolts to the exhaust manifold are removed...thinking of my next move.
As these guys are telling ya, this is not a job to tackle as a rookie, unless you have the upmost confidence in your learning skills. For the assurance of a precision rebuild, it's a job best left to someone more experienced. If the head were something out of the '70s, the task would be alot simpler and more forgiving, as their tolerances were not as tight.
An alternative might be to find a low mileage head and install it. Then you could leisurely rebuild your old one.
 

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If you tackle the job - Once you get the head off (take it to a good machine shop for valve work and cleaning) then you can pull the oil pan off and take off the connecting rod bolts and push the pistons up from the bottom and out the top of the block. If you inspect the rings and cylinders you should be able to tell if they need replacing. The rings seal the piston to the engine and provide the compression you need to make power. A new set of rings will run about $50. Go ahead and replace them. Make sure you put the new ones on exactly as the old ones were. Must have good torque wrench and follow specs exactly or you will be doing this again within a short period of time. AS long as you have it all apart you might as well replace rod and main bearings. Just do one main at the time. Not too hard a job at all. I have done it on my 89 PGL a couple of months ago. You need a manual for sure for specs and all. Good luck.
 

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Discussion Starter · #16 ·
I understand what you're getting at...this is my first major repair job. However, I'm not sure what would qualify me for being skilled enough or not to do this.

Basically, this is an opportunity for me to learn what I AM capable of. Assuming I can't handle it is a self-defeating attitude, one I refuse to have.

I can take my time rebuilding this head. That's not an issue yet. However, I am concerned with making sure I don't have it off too long, and end up ruining the block from it sitting. Is THAT a concern? It's humid here, and the garage isn't cooled.

I found the part in the shop manual that would be most useful, with measurements and such for the head rebuild.

I'll do a compression test tonight using the tsp of oil...just to make sure I've done all I can before pulling it apart.

So now, are there any recommended online part sites, or should I start looking for a jun- er- auto parts recycler?
 

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i remember reading somewhere that supra piston rings fit our car (or was it postons)... anyways i heard they gave a much better seal and prevent alot of blow by, anyone know much about this, just curious...
 

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"Oh, and install the 2-stage thermostat That picture you took of your gauge cluster on the highway is consistent with having a thermostat rated "too cold" for this engine. The temp needle is supposed to sit just to the left of dead center. The reason yours sat quite a bit to the left is because the 180 degree thermostat sets the engine operating temp at about 8-10 degrees lower than it should be (around 188-190C with the 2-stage), so this would make sense. Also, the transient effect of the "cold shock" given by a single stage to a hot aluminum/cast iron (as discussed before) engine is to be noted. This may or may not have led to your head gasket failure."

END QUOTE

Im not saying that he should or he shouldn't install a 2 stage T-stat, but I am saying that It seems unfair to just make the assumption that the 180 degree single stage T-stat is whats causing the problem of his car running cold, and that you may be leading him in the wrong direction. I just want you to keep in mind that it could be somthing else, as I have a single stage 180 degree T-stat and my temp sits at the 1/2 way mark at all times, when its warmed up. It seems to me that his car is running cold because the T-stat is broken and is stuck open, therefor the coolant dosn't have a chance to warm up to 180 degrees because the T-stat is open all of the time and the air from driving will cool it down. So basicly if he replaced his T-stat with a 2 stage it probley will fix the problem since he is putting a working T-stat in place of a broken one. Im willing to bet that if he just bought another single stage 180 degree T-stat it would fix the problem also. but if ylou have the money its probley best to go with a 2 stage, just don't think that a single stage T-stat will not fix the problem because it will, as long as the single stage is working properly. IMHO the only thing a 2-stage does different than a single stage is it warms the car up in a more gradual way, and a single stage will just simply open at 180 degrees. So I think the 2-stage T-stat is just a safty mesure to aid in protecting the block just in case your dumb and you boost on a cold engine. But honstly how many of us boost on a cold engine? NOT ME! and not anybody else if they care about they're car. So basicly as long as you let you car warm to full operating temp ( when the T-stat opens) before boosting, a single stage will work fine. If you have a tendecy to boost on a cold engine or you have a kid that drives the car you might want to go for a 2-stage just to be safe because you never know if they're going to boost on a cold engine.

Also 8-10 degrees lower temp will not cause that drastic of change in operating temp, his gauge was sitting on the 1/4 way mark, which is deffintally WAY lower than 180 degrees, his low temp is due to a stuck (open) T-stat. also you can buy 190 degree single stage T-stats, the 2-stage T-stat isn't the only 190 degree T-stat out there.

Methman
 

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Discussion Starter · #20 ·
Methman...I'm wondering then why I'd have a problem, if my thermostat is stuck open.

Particularly...why it's heating up when the car idles. When I'm driving, it seems to cool just fine, but even if I just stop for a light, it can heat up. And not just to 1/2...it goes a bit past.

It's obvious now that my cooling system is getting air forced in somehow. Regardless of the thermostat, I have a pressurized radiator even if I just start the car and turn it right off.

If there's good reason for a 2-stage, I'll probably splurge and get it, if I can find other parts cheap.
 
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