1999 Olds 3.4 high temp

My wifes 3.4 mini van's water temp started running to the high side two weeks ago taking our daughter to school. She shut it downa dn called me. I drove it home and while it never got into the red, the temp needle kept wandering slowly up and down. I changed the thermostat, didn't help. Next I pulled the radiator to have it checked as it's got 130k plus miles on. Then I decided to just go ahead and replaced it because of the mileage and it having plastic tanks which will crack with age. That didn't help. Next I replaced the temp sensor, didn't help. :banghead: Saturday I totally bled the air and filled the coolant then she drove it quiet a ways and it did fine. Sunday she drove it to church, a 7 minute drive, and it just got into the red and the low coolant light came on as she got there. I checked and sure enough the water is low but there are NO apparent leaks nor is water getting into the oil as it's clean/clear. :banghead: After researching on the net I've found two most likely causes. Either the intake or a head gasket, or both, are leaking. My question is this. Since the rear head is buried underneath the dash and almost impossible to reach, I can't pull the rear plugs to do a compression check on the back three cylinders. Hell, so far I can't figure a way to reach the rear plugs to replace them for that matter. How can I tell if it's either the manifold gasket or head gasket without taking it apart? Normally for a head you check compression but it's impossible in this case UNLESS it happens to be the front head leaking, which I can reach. Personally I don't know of any other way to check unless I take it to a shop to have the coolant checked for exhaust gases. If it's the intake I certainly DON'T want to pull the heads if I don't have to although with the intake off, I'll be half way to taking the heads off then. Anyone with any ideas??? :frown:
Thanks

$20 says it's the heads. Classic symptoms and the intake manifold leak doesn't normally allow that quantity of air into the coolant system where it goes hot-cold-hot-cold as the air bubbles pass by the coolant sensor.

You can buy a chemical test at many automotive stores to check for exhaust gases in your coolant yourself. If you wanted to, you also could do a compression check after you took off the lower intake manifold. Easy access then.

The good news is that you get to replace the intake manifold gaskets as you disassemble the top of the engine to get down to the heads. The bad news is...you have to disassemble the top of the engine to get down to the heads.

Hello.I agree with the above post.I have a 95'Monte Carlo.I'ts doing the same thing as your van is doing.Turned out to be a BHG,(blown head gasket).Had a Olds van last november,It blew the intake gasket.I did not feel like messing around with it,So I sold it.You can access the rear sparkplugs,You have to get at them from underneath.When I had my Olds,It took me three hours to change plugs.I know it is a bear working on thoes engines when they are buried under the hood.That is why I sold my van.The Monte was fairly easy to repair.Sorry you are having problems.But I would also bet that it is head gaskets.Good luck.Diesel 1962

Get the Haynes #38036 Service manual, in Chap 2-18 it explanes rotating the engine which you have to do to get at the rear anything on the engine. Essentially you have to remove the two torque struts from the front of the engine, hook up a ratcheting tie down strap to the engine lifting eye and pull the engine forward.

SAFETY NOTE!! If you are going to rotate the engine and work behind it, make sure you add a safety line in case the one you have on the engine slips off. If it does this it will pin and probably break your arms and you'll have to sit there until the Fire Department arrives.

The work on the engine isn't much different that on other engines just a lot more work. Make sure you change the O2 Sensor and plugs while your there, if the alternator is old you can replace it or as I did rebuild it.
There are lots of tricks and tips. If you decide to give it a try repost and those of us who've been down this road before can give you a hand.
If the leak isn't too bad you can try some ALUMASEAL, it helped me limp home from vacation. Put the sealant in, then warm the engine to pressurize the cooling system, then shut it down to allow the aluminum flakes to fill the hole. Repeat this several times to fill the hole and hope the combustion pressure dosen't blow it back out. It might get you through the winter, good luck.
94

It sounds like the headgasket. If you remove the rad cap and let it warm up idling you will eventually see bubbles coming up in the coolant when the thermostat opens. Playing with the odds it is the front headgasket. The rear head gasket tends to have an external leak as the front ones tend to leak internally.