I don't have the equiptment to do a pressure test, but it might be a good idea to get that done. It heated up just now, but I'm not sure it will repeat (I re-installed the core again).

Couldn't you make up a pressure tester with a old radiator cap and a garden hose fitting? Or you didn't want to water down your coolant, an air fitting from your air compressor (turned down to a low PSI)?

Edit: actually, I guess both of those would be too much pressure... but this could be rigged quickly... Here.

Edited October 31, 201015 yr by SAmadei

Thanks guys, I guess I should own one of those.

Wow... this one is pretty cheap ($59) for a complete kit for a shade tree mechanic... at Harbor Freight.

Decent price.

After consultation with some GM folks and other assorted motorheads, I've decided to run with Stang's idea that the Tahoe's water pump is the culprit. The theory is that the blades of its impeller have corroded to the point that they can't maintain enough flow through the heater core.

While I'm ripping apart the front of the engine, I will also be replacing the leaky power steering pump and hose.

Parts are ordered.

Can't wait, can't wait...

I wish I could wait.

I'm getting a bit tired of draining the cooling system.

Picked up the new water pump, power steering pump, PS high pressure line, PS fluid, and sealant today.

The water pump now has a fresh coat of black high-temp engine paint on it and is curing on the radiator in my living room.

Might have to go get some kero and make room for the Tahoe inside the barn if I want this done tonight.

Then again, I may wait for a warmer day.

...and now my house reeks of paint.

Bailed on this last night, and may do the same tonight. Spent the day on a ladder and I'm kinda beat.

Time to get back to this - tired of having a frosty Tahoe.

Let us know how things work out...I am headed out to the garage to build a work bench myself...

Well, it wasn't the water pump... but I have heat!

My one-year-old serpentine belt was the culprit. As I was replacing the water pump I discovered that the belt was dry-rotted, cracked, and starting to split lengthwise along one of its grooves. Before anyone doubts this being the source of my troubles, hear me out.

I took off the old water pump and decided to take off the back plate to see if the theory that the impeller was rotted away held up. Nope, the impeller was a bit rusty but fully intact and the pump spun easily without any play. The pump wasn't expensive, so I don't mind all that much that I've replaced it - but it wasn't the culprit.

I didn't notice the condition of the belt until I went to re-install it, at that point the new pump was already in place. So, I borrowed a car and went to get a new belt. Upon installing the new belt, I noted that the tensioner was in a dramatically different place than it had been with the old belt. Obviously, the belt had been slipping on the water pump pulley enough that the flow was not sufficient to drive coolant through the heater core in its installed position. So the theory that the pump wasn't pushing enough coolant was correct - just not for the reason we all thought.

I never suspected the belt as it was replaced when I first got the Tahoe - but it was completely shot.

Who knew?

Took a good look at the power steering pump and decided that replacing it was a job for another day. Looks to be a giant hassle of a job. Had I started, I would have been there until midnight.

used car purchase = always replace the belts + fluids and if they are easily accessible, the plugs too.

You never know when they were done last.... and even if the owner told you, just assume that they probably lied.

Cheap piece of mind.

Except that I did replace the belt - it went bad in a year.

The strangest part is that I had no other ill-effects from it. No charging problems, no overheating, no sluggish steering, no belt squealing.

I guess it is a quirk of serpentine belts - one I will remember.

Old stock off the shelf maybe? Or another pulley or accessory going bad while the water pump displayed the first symptoms?

Who manufactured the belt? Dayco, Gates, or some cheap brand?

The belt was unreadable - it must have been a Pep Boys cheapie. I thought that I got it at NAPA, but perhaps not. The thing was very brittle and the flat side was almost polished - looking.

Edited November 30, 201015 yr by Camino LS6

hmmm

pull the belt off and check the tensioner pulley or anything the back side of the belt touches

The belt was unreadable - it must have been a Pep Boys cheapie. I thought that I got it at NAPA, but perhaps not. The thing was very brittle and the flat side was almost polished - looking.

That sounds like a side effect of slipping on the water pump pulley. As Olds mentioned, I would look hard at the tensioner and the belt size... perhaps it was the wrong belt in the sleeve? Too large is going to give you slippage and will generate heat. Too small is going to cause the belt to shred... at least in my experience.

I have the shredding problem with "Dad's" fullsize van. I've been using larger belts, but they are still tight... but there are a few other problems with the accessory drive and water pump, so I'm not going too slack until I fix that. I just wish I could find a guide to the pulley diameters on a '89 Van... it appears stock, but something is definitely not right. Dad had swapped in the engine, and likely used a longer belt, but it also was unreadable when the van threw it. Dad took that secret with him.

Good to see you are zeroing in... I'll have to drag you over to help sort out the mystery cooling issue on the van when I pull it apart next time. ;-)

I think that I have to replace the serp belt on my 07 Impala soon, it's slipping more and more on the power steering pulley.

That sounds like a side effect of slipping on the water pump pulley. As Olds mentioned, I would look hard at the tensioner and the belt size... perhaps it was the wrong belt in the sleeve? Too large is going to give you slippage and will generate heat. Too small is going to cause the belt to shred... at least in my experience.

I have the shredding problem with "Dad's" fullsize van. I've been using larger belts, but they are still tight... but there are a few other problems with the accessory drive and water pump, so I'm not going too slack until I fix that. I just wish I could find a guide to the pulley diameters on a '89 Van... it appears stock, but something is definitely not right. Dad had swapped in the engine, and likely used a longer belt, but it also was unreadable when the van threw it. Dad took that secret with him.

Good to see you are zeroing in... I'll have to drag you over to help sort out the mystery cooling issue on the van when I pull it apart next time. ;-)

Everything seems good now with the new belt.

But, I think you guys may be on to something with the belt size issue. NAPA lists six different belts for a '95 Tahoe - I could have gotten the wrong one last year (especially if I did get it from Pep Boys).

As for the van, I imagine that changing the belt on it is a real PITA - but I seem to be a glutton for punishment, so drag away!

The next go round for the Tahoe will be the power steering pump - it promises to be a real hassle. Then, it will be the sway bar end links, tuneup, oil/filter change, lube, air and fuel filters, and inspection.

I may have the shop rebuild the door hinges - too much of a hassle to do without a second guy.