overheating 95 caprice wagon LT1

i have a 95 caprice wagon since new, 132k miles with the lt1 and it overheats on hard acceleration such as melding on a interstate ramp etc. seems to run with temp in the middle around town. The chevy dealer found the primary electic fan stopped as well as faulty pressure cap on the recovery tank. These items were replaced and the cooling system was flushed. ran ok for a couple of months and now noticed it heating up again on passing type of acceleration. would lean toward possible plugged cat convertors on the dual exhaust but it has not lost any power. remains strong and torquey. any ideas?

Could be a collapsing lower radiator hose.

Or a clogging radiator, or a failing water pump or pump drive coupling (plastic sleeve), or a thermostat problem, including the lower disc falling loose from the stem where it's riveted on (the LT1 uses a two-tier thermostat for the reverse-flow cooling system).

And it's an expansion tank, not a recovery tank. Coolant should be flowing through it at all times, at least from the small bleed hose.

OK thanks to CD and Bowtie, will try the cheap and quick and change out the lower radiator hose first. It appears weak. Thermostat and expansion tank were swapped in earlier effort.

is the water pump belt driven?
it could be as simple as a loose belt

The water pump is cam driven on the LT1 I believe.

swapped out the lower radiator hose and that did not do it. water pump is driven via cam gear.

When you refilled with coolant, did you properly bleed the system?

I'm not sure of the exact procedure, but I know there is a method to bleed the LT1s so you don't end up with steam pockets. But I think that would show up all of the time.

Blue Bowtie?

Does the car have a high rate of fuel consumption? Any MIL?

Check that the radiator is unrestricted - if you see any calcium buildup in it at all, it might need to be 'rodded'.

My guess is the problem is one of cooling capacity if you're absolutely certain that both exhaust systems are unrestricted. This would point to a (partially) clogged radiator.

The water pump is driven by the cam, but via a plastic sleeve coupling. With any kind of wear or stress, it can fail to drive the pump at higher RPM. You should be able to simulate that with the hood open, since the phenomenon is not related to load, but simply engine and pump RPM. Detecting the slippage may be difficult, however.

Load-related cooling capacity problems (not just RPM) are more commonly coolant flow restriction (often at the radiator) or restricted exhaust, as silicon advised. Other, less common causes are late timing, lean mixture, eroded water pump impeller, or serious internal engine cooling system blockage.

Bleeding the air is important, and can be difficult. I had quite an episode with my '94 after some work, and actually ended up raising the front of the car, opening the bleeders, running it, and filling / bleeding for at least a half hour. I ended up watching the expansion tank and adding several times over a week or more untill it finally purged all the air. That was on a completely empty block, however.

the mpg seems to be about 21 on the interstate which is normal. when replacing the lower hose I let it drain into a container and it looked like six quarts or so. poured new coolant down the top of the new hose and reattached then added water to the expansion tank and bled it via the screw at the thermostat neck. Is there more than one bleed screw? warmed it up and let it cool down and added more to expansion tank and seems to hold at the proper level.
Now have a new problem with alternator on the discharge side. Battery is ok. This will be the fourth alternator in 132kmiles.
I think I will jack it up and drive a new 07 LTZ Avalanche under it.

Today a radiator shop rodded the radiator and replaced the side tank on the radiator which had a small crack. Flushed block and heater core good and now she is running normal again on hard acceleration. The radiator was 85 percent crudded up with block scale and deposits so the problem was caused by low efficiency of the radiator. It's a credit to the design that it didnt run hot all the time.

That was a great find, I knew it had to be a coolant-velocity issue. I had bought a radiator for my '79 wagon and moved it to my '84 when I got that. I was amazed at how cheap it was at the time, something like $119 at Auto Barn.

Bob