A real stumper GM 305 :(

I've got a real weird one on my hands and am asking for advice. 92 Caprice with 310,000 miles on original 305 engine.
For the last 3 years or so I have not been able to just flush/fill and
put a stock thermostat in the car and have it work properly.
The heater core, all hoses, radiator and several different brands of thermostats, new cap (3x) (195 degree, but I tried 190 as well) have all been changed. The water pump is about 4 years old but shows no signs of trouble.
Here is what happens:
1. Raise front of car on ramps and fill the system leaving the radiator cap off. Run engine until thermostat opens and then top off the coolant with 50/50 mix.
2. Let car cool down and do the same thing again until level in radiator stays the same all the time, at the top of the neck. Fill up coolant overflow jug half way. Put on cap and test drive car.
3. Temperature gauge (cold car) will start to rise slowly then go way up almost until redline, sit there for a few seconds and then the gauge will drop like a rock down to normal. However, the gauge will still swing more than it should after this point although it will NEVER go back near the red.
4. Drilling a small hole in the edge of the thermostat fixes the problem and the car runs fine.
Observations:
1. I do not lose any coolant. 2. I DO see some bubbling in the radiator, but nothing that I would attribute to anything other than the coolant sloshing around.
So far it has been suggested that I have a head gasket problem, but I doubt that because like I said I have been driving for 3 years like this (hole in thermostat of course). I put A LOT of miles on this otherwise perfectly running car. Oil is clear, coolant is clear and exhaust gas doesn't smell sweet of anything. I just changed plugs and they looked fine as well.
Water pump cavitation problem?
Air trapped in the system? I have left it overnight on the ramps with the cap off and still have the same troubles.
Should I get a new thermostat housing and put a bleeder valve on it?
Any other ideas?
psycho
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Long ago I actually had a call into techline for a problem just like this .It boiled down to the water pump... I don't know the reason, but It was the ater pump.. It may be happening because when cold the cooling system has no pressure and sucks a small amount of ait by the seals and causes an air pocket in the head, or maybe just a cavitation problem..I don't know, I do know I have changed a lot of pumps on these for this problem, and they have been fixed.. They aren't a lot of money, and if it's 4 yrs old, it should be due for a failure pretty soon.....Bobo

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Thanks for the quick reply Bobo! I'm gonna change the pump this week and see what happens. This pump has always made a very slight knock that has driven me crazy anyway and like you say, it's time for a replacement before it dies in the middle of February when it's 10 below outside!!
I'll let you know how it works out!
psycho
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4 years from a WP and it's due for replacement? Guess I need to get mine done before winter, will be 4 years in Nov...

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4 years???? Must be a cheap pump... I have a 94 with factory pump/ 128,000 miles on the 4.3 and a 95 with 98,000 on a 350 with factory pump Both tight and no leaks, if your getting 4 years on a pump you might want to check the belt tension on driven items.
--
Steve

"Mike Levy" < snipped-for-privacy@levyclan.nospam.us> wrote in message
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Mine's not factory, not planning on replacing my pump till it leaks or fails to work. I was shocked to see the suggestion of replacing the pump every 4 years...

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On Mon, 13 Oct 2003 05:51:12 GMT, Mike Levy

1. I'm having a problem with the car and this is the last piece of the puzzle.
2. He didn't say replace it every 4 years, he said in this case it might be a good idea. Maybe the pump had a defect in it. It also has over 150,000 miles on it. It's more the mileage than the time.
3. Guess when it's going to "fail to work"? Yep, on 4th of July weekend in 100 degree heat while you are stuck in traffic. And when you see the bill for the fried engine, towing and the mechanic who knows you are stuck out of town and is going to take you to the cleaners, that's when you will be shocked! I see cars stuck in NYC with steam coming out of them all the time. I'll bet they were waiting for parts to fail before they replaced them as well.
On my car it takes less than 1 hour, costs less than $50.00 and might just fix my air pocket problem.
For me it's worth the $50.00.
Would I routinely change a water pump every 4 years?
No I wouldn't.
Would I routinely change one with 150,000 miles on it?
If it was easy and relatively cheap I would certainly consider it because it is a mechanical device and it will most definitely wear over time.
I change my hoses every 3 years or so anyway.
psycho

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On Mon, 13 Oct 2003 17:03:55 GMT, psycho snipped-for-privacy@yahoo.com wrote:

That's how I understood BoBo's post. Here's a quote "They aren't a lot of money, and if it's 4 yrs old, it should be due for a failure pretty soon.....Bobo" I get from that that he's suggesting replacement every 4 years. I don't put NEARLY the number of miles on that you do, maybe 15,000 a year if I'm lucky. I got this truck in July 98 with 60,000 on the clock, it now has 114,000 on the clock.

My father is that way, even if it shows SIGNS of imminent failure, it's not getting replaced till it fails.

Mine are originals, 10 years old. Cooling system still works perfectly, so they aren't getting changed any time soon.

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On Mon, 13 Oct 2003 17:13:17 GMT, Mike Levy

Yea I see your point. My experience with GM big/medium block V8's is that corrosion sets in and the pump, generally the impeller, usually lets go before it starts to show any signs through the weep holes.
However, all of these beasts are different!

I have a friend like that!!

My father always said "if it ain't broke, don't fix it!!" I'd take a look at the hoses though, because the rubber decays over time. Unless you have the silicone hoses used in the LT-1s and so forth.
As for the pump, keep an eye on it and look for weeping or noise.
psycho
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On Mon, 13 Oct 2003 19:28:00 GMT, psycho snipped-for-privacy@yahoo.com wrote:

Pump is 4 years old, replaced as a result of an accident. Hoses do seem fine, don't look deteriorated or anything, and I use no chemicals on them.
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Borg Warner pump I believe. There is about 150,000 miles on mine. See my other post.
psycho
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On Mon, 13 Oct 2003 04:07:19 GMT, Mike Levy

4 years and about 150,000 miles. It's the mileage, not the time and like I said, better safe than sorry especially since it takes me less than 1 hour to change and cost less than $50.00. One way or another I have to fix the problem and this is the last piece on the puzzle.
One of the reasons my car has 310,000 miles on it, does not burn an ounce of oil and still has the original engine and tranny is because I try to fix little problems before they become big problems. I also change the oil and filter every 3k miles and use Castrol GTX and a Wix filter.
psycho

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<
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Alan "A.J." Franzman
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On Mon, 13 Oct 2003 07:10:58 GMT, "Alan 'A.J.' Franzman"

It's too nerve racking for me wondering when / if the thermo is going to spring open :)

Do you have a google link? I'll take a look.
psycho
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< (without quotes) into the "Message ID" box. Click the "Google Search" button.
Thanks.
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Alan "A.J." Franzman
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Dude, sorry to piss off everyone so much they stopped trying to help you and had to try and bury me.. Whatever they want to say they can, just let everyone here know if you do try a pump and how it works out for ya.... I myslf have seen pumps fail a hell of a lot sooner than 4 yrs, mileag.. I have also seen them go a hell of a lot further too,, but like you said.. What's left besided an expensive head job you may not need.... I'm not bitching about the flaming .. let em have fun.. Bobo

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Well they can laugh all they want Bobo, but your advice to replace the water pump fixed the problem!
I put it in this morning, filled the system and put in a normal thermostat without a hole drilled in it and the car seems fine.
FWIW the old pump seems ok but the impeller shaft has a little more play in it than the new one. After 100,000+ miles I would expect that. The shape of the new impeller is a little different as well.
Thanks again for the advice!!
psycho
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