Mysterious Coolant Loss

[OUMike]

So about a month ago we changed the water pump in my 94' 4.3. Everything looks fine now. No drips, no apparently leaks of any kind. When I fill my overfill case on the firewall to the cold line and run the truck for a couple days I notice that it becomes empty. If I let it go long enough I'll see the radiator will become a little low. I can't find any leaks anywhere.

 

Ideas? Thoughts? Questions?

 

As always, thanks a lot!

[Draenor]

I just noticed I am going thru the same thing myself at the moment too. Haven't isolated it yet. First thing I would do is check the oil. Make sure it doesn't look all milky. If it is, the head gasket is letting coolant leak into the oil.

[snoman]

Those 4.3's has a nasty habit of developing intake manifold leaks. (Some of the 350's were not much better) Check for coolant tracks down the back of engine and bell housing.

[OUMike]

I just noticed I am going thru the same thing myself at the moment too. Haven't isolated it yet. First thing I would do is check the oil. Make sure it doesn't look all milky. If it is, the head gasket is letting coolant leak into the oil.

 

Yea, thats what I thought too. Oil looks good, so fortunatly no trouble there.

 

Those 4.3's has a nasty habit of developing intake manifold leaks. (Some of the 350's were not much better) Check for coolant tracks down the back of engine and bell housing.

 

Very interesting. I think that will be my next stop. Thanks snowman.

[rdnkcpa]

My 99 Astro did the same thing. It turned out to be the intake manifold gaskets. After the engine got good and warm you could see the coolant leak out of the back of the intake right behind the distributor. Evidently the 4.3's are known for this. On my van it was a pretty big job for a non mechanic.

[OUMike]

I've heard rumours of this being true with the new 4.3s with plastic manifods. Mine is 94, so its definatly metal. Could this still be a problem?

[snoman]

I've heard rumours of this being true with the new 4.3s with plastic manifods.  Mine is 94, so its definatly metal.  Could this still be a problem?

 

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Yes it is still a problem. GM even redesign the gasket for them a few years ago because of it. You can pretty much bet the farm on it being the intake gasket.

[decee]

 

LINK to class action lawsuit of the junk GM uses

[TEE]

Anytime you design a gasket that does not cover either front or back oil valleys and have to use RTV to seal is a pisspoor design PERIOD!

I know...been there and done it many times.

I can tell you that GM does have a newer redesigned gasket for the 88 to 98 350's that were also a problem. The older ones didn't compress.

I just put a set on my new engine and they do look better....

[OUMike]

Okay, so lets assume this is my problem. Leaky manifold gasket. I wanna change that now. How do I go about doing it? What all has to be removed? To what torque specs do those bolts need to be retightend to once the gasket is reapplied?

[larry arizona]

Just did head gaskets on my Dads 1992 4.3. It may have been a chain of events that started with the manifold gasket , lost coolant overheated and then blew head gasket. Head was warped. Not too bad of a job but may depend on how much room under the hood you have. His PU had tons of room and was not that bad. Two afternoons total.

[snoman]

Okay, so lets assume this is my problem.  Leaky manifold gasket.  I wanna change that now.  How do I go about doing it?  What all has to be removed?  To what torque specs do those bolts need to be retightend to once the gasket is reapplied?

 

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I am thinking around 30 to 35 ftlbs (I would need to double check though) but it is VERY important to start in center and work out and bring them down slowly (like 10, then 20 and then 30 ft lbs) to spread stress and properly seat gaskets

[rdnkcpa]

Okay, so lets assume this is my problem.  Leaky manifold gasket.  I wanna change that now.  How do I go about doing it?  What all has to be removed?  To what torque specs do those bolts need to be retightend to once the gasket is reapplied?

 

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My Astro van was difficult to work on because of being a van. I don't know what your mounting brackets for accessories look like, but on my van the bracket that holds the Altenator had to come off I had to loosen but not remove the A/C compressor, remove the distributor, fuel lines, and the top half of the manifold. I could have left the top half on, but it was much easier to take apart to get it out of the engine comparment. My manifold is two pieces. A top plastic piece that holds the TBI, and a lower aluminum piece. I bought a gasket set that includes the intake gaskets, TBI & distributor gaskets. I think it was $39.00. Somebody posted that the torque settings for the intake are 80 inch pounds. You may want to verify that in a Chevy shop manual. Its a bear of a job, but not impossible. I'm an accountant by trade and I was able to get it done over a couple of Saturdays. I went slow and made sure I did'nt twist any bolts off. Plus it gives you the oppurtunity to really clean your intake manifold & injectors.

[Wingnut]

It's 35 lbs, and they need to be done in two stages, in the right order. You can probably do it in a few hours, depending on your skills and tools of course.

 

I can scan the diagram for you later...PM me if you want it.

[rdnkcpa]

It's 35 lbs, and they need to be done in two stages, in the right order. You can probably do it in a few hours, depending on your skills and tools of course.

 

I can scan the diagram for you later...PM me if you want it.

 

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35 foot pounds is 420 inch lbs. If you crush those gaskets all your hard work will be for not.

 

Snoman--I asked the same question and you responded 44inch pounds first pass, then 80 inch pounds second pass. So which is 35 FOOT pounds or 80 inch pounds?