Plummeting gas milege (8mpg) – the saab link forums gas line jobs in wv


I am experiencing significant gas mileage loss and some weird symptoms that I do not understand. After consulting a mechanic he suggested the turbo was the issue and to see if I was getting white smoke upon start up. Here’s some background to the car.

To remedy the gas milege I began doing a full inspection myself. Dropped the pan clean enough. Looked inside cool. I changed the plugs with the correct NGKs torqued em lubed em up with some dialitic grease-beuno. Immediate improvement. And with an oil change every 2500 miles the car ran great. Gas mileage was a solid 20, not bad still low. And then as it got hot for summer became ever lower down to 16.

Down the road maybe a month or two I got a code for sooty plugs (P1312 I believe) pulled em out sure enough they were grimey. Dang, changed them again, back to 20. A week later dirty plug code comes on again. Then goes away within the day. I decide to change all the vacuum lines. No real improvment. The next day I pop open the hood after work a bit of white smoke was coming from behind the engine eminating from the area behind the ignition and in front of the oil cap. No real tangible location I could see. There wasn’t mucj of it. Didn’t have a particular smell I could identify. Shoot, I think "we’ll I’m doing some work changing the timing belt engine mounts soon I’ll get to it." The next day the whote smoke is much worse, but still not a crazy amount but suddenly the gas mileage is PLUMMETING 11, 10, 9… even as it idles. No significant smoke from the exaust. Theres a strange smell in the cabin not antifreeze or oil just weird. Oil looks normal…. What is happening to my baby? What more info can I provide?

I just thought of something that’s more likely: coolant temp sensor and thermostat. They’re cheap. One of the failure modes for the coolant temp sensor is to read artificially low temperatures, when that happens you won’t get a code, and the engine management continuously runs in enriched warm-up mode. That’ll give you bad gas mileage without other symptoms (except that it won’t run the radiator fan unless the AC is on, you won’t actually see an overheat if you use the AC all the time). And if the thermostat gets stuck open, that’ll also cause too low coolant temperatures and running in warm up mode.

As far as testing for a fuel leak, I’d just turn the car on and lift the plastic cover and do a visual inspection for wetness while it’s running. You could have a leak AND something else wrong too–seeing white ‘smoke’ isn’t explained by a bad temp sensor and/or thermostat. Maybe you have a coolant leak back there? The throttle body is in the coolant circuit so that it doesn’t ice up when it’s cold out. Coolant dripping onto the cat makes a sort of sweet smell. Maybe that’s the smoke?

Number one I’d try replacing the coolant temp sensor and thermostat (and plugs if they’re wrecked again) before doing anything else. While you’re back there at the temp sensor, make sure to inspect/clean-up the grounds to the intake manifold and block(?) too, I think there are two there under 10mm bolts if I’m remembering correctly.