1984 Chevy Truck Trouble after coolant system flush

HALLC

MEMBER
1984 CHEVROLET TRUCK

Engine Cooling problem
1984 Chevy Truck V8 Four Wheel Drive Automatic? Miles

I bought my truck a year ago and was not sure if the previous owner had ever flushed the coolant system, so I flushed it last weekend. Ever since then, my truck has been acting strangely. The transmission does not seem to want to shift into 2nd gear anymore at slow speeds. For instance, when I am driving at about 30 mph, it sounds like the fan under the hood is spinning really fast and the RPMs are high. When I pass through about 35 mph -- with my foot only lightly on the gas -- the transmission suddenly shifts with a giant lurch. On the highway at 55 mph, it sounds like the engine/fan is working really hard. It feels like the transmission is in a lower gear than it should be in. The transmission has never done any of this before.

Also, I've noticed that when the engine is warming up, it passes the temperature that used to be the maximum warmup temperature by a noticeable amount (though not into the red zone on the temperature gage). The temperature then drops back basically to the regular operating temperature, but then afterwards the temperature begins to fluctuate a little up and down. It doesn't stay constant. Before I had flushed the coolant system, I had noticed the operating temperature fluctuation before, but I have never seen the engine heat up so much before dropping back to operating temperature.

After the coolant flush on the weekend, I refilled the radiator. When I take the radiator cap off, the fluid is all the way to the top. I don't see any coolant leaks. I checked the the fluid with a hydrometer, and it says I have a 50/50 mixture, just like I should.

I replaced the thermostat a year ago. Do you think it has gone bad? The engine is a rebuild. I have no idea how many miles it has on it, but I think more than 100,000. Is it the water pump? Can a faulty water pump cause the transmission to shift improperly? When I grab the pump pulley, there is a very small amount of movement. I don't see any evidence of coolant leaking out of the weap hole, though.

Can you tell me what's causing these problems?

1 Reply

MERLIN2021

MECHANIC
17,250 POSTS

Hall, if the temp gauge fluctuates, it is probably air bound, if you can get the front of the truck jacked up a foot or so, remove the radiator cap and warm the truck up. It should burp the air out of it. If not remove the tstat, drill an 1/8th hole in the flat metal part and reinstall, this will allow any air bubles to pass into the radiator and out. Overheating can cause erratic shifting, but a quick check of the tranny fluid for good color and level wouldnt hurt!