98 Venture Overheating

My 98 Venture overheated last week after a short drive, temperature gauge went to hot and hi temp light came on. After it cooled down while driving home gauge would go to hot and then drop back down to normal, very quickly. I replaced water pump and flushed the coolant (I am not sure if I completely bled out all the air, every time I opened the bleeder by the thermostat more air would come out, i repeatly bled over a couple times heating up the engine and then cooling). The check engine now comes on sometimes solid and sometimes flashing according to AutoZone my error codes are throttle position sensor low input and cyl #3 misfire. Also my low coolant light comes on intermittently.
Couple of questions:
Should I keep trying to bleed out air or am I just wasting my time.
How can tell if it is my intake gasket
Is there anything else I should be checking

With the symptoms you described, I'd look into a failing head gasket. The air in the line is being "injected" into the cooling system. The air bubbles the get trapped, allowing the coolant sensor to quickly heat up. When the air bubble pass, the sensor cools quickly, bringing the temp back down to "normal".

The misfire may be from antifreeze entering the combustion chamber. The flashing check engine light is indicative of a major misfire. Major misfires can cause your cat converter to overheat, literally catching fire with the unburnt fuel in the exhaust gases.

Thanks CDRU
I am going to try and replace the head gasket myself, any estimate of how long this will take.
Do you recommend doing anything else while I have everything taken apart. Based upon other comments in this forum I wondered if I should replace the intake manifold gasket also.

When I did my head gaskets, it was probably 20-24 hours total work but that was at a somewhat relaxed pace.. This was also after I've did my intake gaskets twice so I knew what I was doing to get down to the heads. If you've not worked on the engine before, you can probably add some time to that figure.

There is a whole list of other things you are going to replace in the process. Most actually relate more to the intake manifold gasket then the heads themselves. You will have to take off the intake manifolds anyways, so it's a no-brainer as to if you should replace them now or not.

This thread (http://www.automotiveforums.com/vbulletin/showthread.php?t=467461) has a list of all the different things that you should replace. In addition, you will need the head gaskets and the exhaust manifold gaskets. Be sure to get the OEM intake manifold gasket. After market or OEM is optional for everything else.

Check out these threads for more information on the process:
Intake gasket main page (http://www.automotiveforums.com/vbulletin/showthread.php?t=321467)
More Overheating (http://www.automotiveforums.com/vbulletin/showthread.php?t=372853)
97 Trans Sport Heat Removal (http://www.automotiveforums.com/vbulletin/showthread.php?t=429271)

The More Overheating thread has a bunch of tips I wrote up regarding the whole process.

After everthing was all said and done, the total head gasket repair cost me probably around $350. That included resurfacing the heads (recommended but not required unless the heads are warped), pressure testing the heads, and removing 2 broken exhuast manifold studs.

If you get stuck with anything, feel free to send me a PM and I can try to help you out. I usually check in here a couple times a day and before I go to bed, so I'll probably see it within a few hours. Unfortunately the whole process it's still fairly fresh in my memory. It was starting to escape me, but having to do the head gasket in my Cavalier caused a regression. :)

Thanks CDRU
I have my engine down to the rocker arms, the intake manifold was definitely leaking my valve covers and intake manifold had whitish colored sludge. I have a couple of questions.
1. Since I am already this far should I go ahead and replace the cylinder head gaskets
2. Where is the oil pump shaft o-ring that you replaced
3. Where did you buy the o-rings you replaced on the cooling system
4. Did you reuse the O2 sensor

1. Since I am already this far should I go ahead and replace the cylinder head gasketsThat's really not a question I can answer. IF they aren't leaking, there isn't techincally a reason to replace them. Head gaskets aren't really "preventitive maintainace.

That being said, you will never be closer to the heads then now. It's been a few months, but to get the heads off at this point, I beleive you basically have a engine mount (left front) and the exhaust manifolds to deal with, then the head bolts. The 6 bolts on the cross over pipe are easy...they'll just snap off and you can remove the studs from the manifolds when the manifolds are out in the open (much easier). Take out each head with the exhaust manifold attached and remove the manifolds on the workbench.

You will be looking at around $50 for the head gaskets, $50-60 to have the heads cleans, planed, and pressure checked, and $20 for the exhast manifold gaskets ($ are guesses to what I though my costs were). Toss in some new bolts for the exhaust cross over pipe. Also, you can expect the exhaust manifold studs to give you some trouble so you many need to have some studs removed/replaced depending on where they break.

So you are looking at up to about $200 in costs and another 4-6 to get everything off/on. But if it saves you all the time of having to remove the intakes again.... If I had the money, knew of what it took to get to this point, and knew the track record of the head gaskets...I probably would do it. But I know only the latter two and never have any of the first. :)

2. Where is the oil pump shaft o-ring that you replacedIf you look here (http://img169.imageshack.us/my.php?loc=img169&image=40jt.jpg), you'll see a silver cap about an inch across in the middle of the block on the right hand side. This is the oil pump drive shaft cap. You'll need to remove the bolt holding the bracket on, then lift the shaft up. When I removed mine, I used a pair of channel lock pliars and a pry bar to lift it (2-man job) but you may be able to rock it out. Don't worry about dinging up the cap, it doesn't matter functionally. Once you lift the shaft out, you'll see a o-ring that likely has hardened. Eventually it will allow oil to leak out from under that cap as direct, full oil pressure direct from the pump runs under it. I just used a tiny screwdriver to break the old o-ring and removed it and slipped the new one on. Reinstallation is reverse of removal. If the square drive shaft keeps slipping out, put a little grease inside the hole in the cap then push the shaft in. It will stick more then. You'll see what I mean once you get there.

3. Where did you buy the o-rings you replaced on the cooling systemDealer. They probably can tell you what they are off the top of their head. But if not, they are easy to look up. They are only a few bucks total.

4. Did you reuse the O2 sensorI did because I had recently replaced mind and didn't have the extra $80 for a new one right then, but if you have high miles it's recommended to replace it. You will never have an easier time getting to it. I took the chance knowing that I would have a harder time replacing it later if needed.