fixed my car, lost my gas mileage

[SUPERDUTYD]

i have a 1996 3100 monte carlo that i put new upper and lower intake gaskets as well as o2 sensor, plugs, wires, 195 thermostat, coolant flush, cleaned entire fuel system, etc... i used to get around 325 miles on a tank of gas and now i get 225. i passed emissions and it runs fine but i must have screwed something up. i did notice before i did the work that my temp gage went to almost the 1/2 way mark and pretty much stayed there, but now it barely gets to the 1/4 way mark. i figured this might be the problem so i replaced the thermostat again but no change . any ideas?

[SigEpCutlass]

tire pressure? coil packs? ...

[Brian P]

did the temperature sensor get damaged in any way during the job?

[SUPERDUTYD]

i was thinking the temp sensor too. i did remove it and "clean" it with a scotch brite pad when i was fixing the car. does that sensor feed the temp gage also?

[THe_DeTAiL3R]

My temp guage used to read 1/4 when I first had my car, now it goes a little past 1/3rd.

 

I also change my LIM gaskets recently, but I think the shitty mileage is due to the additives in winter gas. I noticed the same thing last year.

[Brian P]

i was thinking the temp sensor too. i did remove it and "clean" it with a scotch brite pad when i was fixing the car. does that sensor feed the temp gage also?

 

starting in '96, yes 1 sensor is for both the PCM and the gage.

[Crazy K]

i was thinking the temp sensor too. i did remove it and "clean" it with a scotch brite pad when i was fixing the car. does that sensor feed the temp gage also?

 

starting in '96, yes 1 sensor is for both the PCM and the gage.

 

HEY is it worth upgrading? junk both old sensors for the new three prong one??? I know I read about people doing it to lt1 engines for the same time period, i think.

[slick]

Was your 02 sensor bad? Could be a bad catalytic convertor if it was bad, but that wouldn't be the problem your having.

 

Faulty temp. sensor is my guess. Check your vacuum lines as well.

[Brian P]

i was thinking the temp sensor too. i did remove it and "clean" it with a scotch brite pad when i was fixing the car. does that sensor feed the temp gage also?

 

starting in '96, yes 1 sensor is for both the PCM and the gage.

 

HEY is it worth upgrading? junk both old sensors for the new three prong one??? I know I read about people doing it to lt1 engines for the same time period, i think.

 

Well I did it when I first got my olds. Transferred it to the 3400. Gage acts about the same just doesn't fluctuate as much.

[SUPERDUTYD]

i put in a new temp sensor, and waterpump cause it was noisey. now the gage constantly moves from less than 1/4 to about 1/3. the heat isn't really that hot either. could it be an air pocket? i cant' believe my luck, iv'e had so many cars that i have been trying to get running cool like this, but the one time i don't want it to run cool, it does.

[Brian P]

i put in a new temp sensor, and waterpump cause it was noisey. now the gage constantly moves from less than 1/4 to about 1/3. the heat isn't really that hot either. could it be an air pocket? i cant' believe my luck, iv'e had so many cars that i have been trying to get running cool like this, but the one time i don't want it to run cool, it does.

 

With the lack of heat and fluctuation it sounds like an air pocket. After a waterpump job, the system does need to be bled of air. There's a bleed screw on the t-stat housing, open it when you get the engine warmed up.

[SUPERDUTYD]

i opened the bleed screws by the waterpump and t-stat housing. i was just wondering if somehow some air was left trapped in there, maybe a gasket problem? i know on my 1990 eagle premier i had to bleed the cooling system every 2 weeks to get heat in the winter or keep from overheating in the summer, and i never lost coolant. i will bleed it a few more times and hope i fix it. by the way, should i be bleeding it while the engine is running or doesn't it matter? maybe i will try replacing the radiator cap too.

[THe_DeTAiL3R]

i put in a new temp sensor, and waterpump cause it was noisey. now the gage constantly moves from less than 1/4 to about 1/3. the heat isn't really that hot either. could it be an air pocket? i cant' believe my luck, iv'e had so many cars that i have been trying to get running cool like this, but the one time i don't want it to run cool, it does.

 

My car is doing the EXACT same thing right now. It goes up to 2/3 or so, and in only a few seconds will go back down to 1/4. Maybe I'll try opening up the bleeder screws when it's cold and leave them open until it's totally hot...

[SUPERDUTYD]

i replaced the radiator cap and it runs closer to normal. by the way, the radiator cap the auto parts store sells is a 16 psi and the factory is a 15 psi. it actually runs a little hotter with the 15 psi, plus the dealer part was the same price and looks better also. i heard the higher the pressure the more efficient the cooling system runs, which might explain a little.

[PCGUY112887]

The popoff on the radiator cap is just so your coolant can't build up so much pressure that something pops, 15psi to 16psi cap should not matter unless you were blowing it off all of the time for some unknown and proball bad reason.

[SUPERDUTYD]

it seems alot of people at mymonte have this same problem. i heard it is possible that the thermostat was moved during replacement leaving a space for coolant to always bypass the thermostat. anyone else have this problem? also, i used non gm intake gaskets, hope thats not part of the problem. i knew i shouldn't have used them, they just don't look as good as the gm ones.