Quote:
Originally Posted by rodcain
'98 w/3800, approx. 120k mi.
I was losing an entire overflow tank of coolant per week
for about 3 weeks in a row and gas mileage dropped.
Of course I thought my upper plenum was bad. Then it stopped completely and decent mileage has resumed.
What is happening?
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You may have a different leak at water pump? Has it been replaced? Check carefully using a mirror to look inside pulled where the weep hole may leak leaving a brown trail of dried DexCool or sealer.
Check the o-rings where the elbow goes from the upper manifold into the the idler pulley braket and the coolant goes through there to the heater hoses.
Checking for leaks after a long drive in warmer temps is when the pressure in the system may make a leak more noticeable.
Check around the perimeter of the upper intake manifold looking for the telltale brown trails.
If your car had DexCool drained out early or the DexCool has been drained every 2-3 years and refilled with fresh and the system has not had contamination with regular coolant added to the tank to cause globbing of the DexCool, you may not have a leaking upper intake.
Just keep checking and being sure the radiator itself is full and the reservoir tank is up to the cetain mark and then recheck at same conditions outside with car totally cold after overnight and parked level. See if it's losing coolant.
Have the spark plugs and wires been changed in the last 40-50K miles?
Did you change gas stations or brands? Extra cold weather and higher alcohol content really hurts mileage.
Idling to let car warm up in cold weather is especially bad at lowering mileage. If you can, start driving gently to let the car warm up after just a short period of runtime after starting it.