Just Had my TB package installed. Prior to that I did the Seafoam treatment (1 bottle in the tank, 1/2 in the intake - (slurp-sip - hard driving 25 miles), 1/2 in the crankcase).

Then off to O'Hare Honda where they changed my TB, water pump, hydraulic tensioner, idler pulley, dry belts, thermostat and spark plugs. The car runs great, no lights on, bu my MPG is 26 on the same stretch of road where I was getting 30-31 for the past two years in a row.

Any ideas ? Was it the seafoam, or the TB install? Does not make any sense to me, with new plugs and seafoam I should get better MPG, not worse

 

Could be winter gas vice summer gas. Not sure when they switch over.

 

I'll go with the gas theory whether it's winter gas or just a different borderline bad gas. Get more miles for a better average. At work we just got a bad batch of gas for the fleet cars and work trucks and the first thing I noticed was terrible gas mileage and eventually a check engine light with a misfire. All it takes is a little water contamination and it can run good enough to not set off any check engine lights but significant enough to affect mileage.

If the timing belt were off by even a tooth, the car would be almost undrivable. I don't like Seafoam especially used in the crankcase and through the intake. It's hard on the engine, it's a solvent so it thins and reduces lubrication. You're so much better off just using an ester based oil for the car's entire life and you will never have to worry about cleaning anything.

 

It's early September, would they change the the gas now ?

I've had this car for two years, never noticed the MPG drop - always had 30-31 highway - with the same tires/same repeated trip/always with 93 shell gasoline , always on 80 mph cruise control

Logically because this happened after the dealer service - they did something.

On other thing I've noticed - the temp gauge - isn't that supposed to be right in the middle when the engine is at running temp ? Mine is slightly towards the cold side -maybe the engine running at colder temps could explain the drop in MPG

But the new thermostat was Honda, just like all the other parts.

Ideas ?

 

The gauge is buffered to keep it from moving out of the middle during normal temperature variations. If you can see a difference, the engine is running significantly cooler than normal.... assuming the gauge is ok.

If it is running cooler this could account for the lower mpg. It's less likely in new cars that go closed loop so early on with widebands but it's possible. Does power feel slightly better?

It can still be the gas. All it takes is one bad load of fuel and it can happen to any station. How did you average the mpg and over how many miles?

 

EPA regulates summer gas requirements from May 1 to Sept 15, so winter gas could be in the stations starting on Sept 16. If you bought that tank of gas before Sept 16, then it probably isn't winter gas.

 

I don't think it's the gas - my driving destinations take me to gas stations on average 200 miles away. 80% of the time i use 93 Shell the rest, top octane BP.

The MPG drop was evident the first drive after the TB package was done.

To be honest, after the Seafoam, the car is "pulling" much better. But I look at the MPG on expressways - as I said, 80 mph cruise control - no "lead foot"

I use to get MPG like this last winter, when I changed to meaty Altimax Arctic winter tires. When I changed back to all-season Kumho Ecsta ASX - MPG went back to 30-31 instantly

 

Well, one tank doesn't tell you anything...

1. If your engine isn't running rough and not giving off CEL or throwing codes, it's highly unlikely the TB is at fault.

2. If anything, I'd attribute "pulling better" to the new spark plugs, not the sea foam.

3. Mileage decrease could have simply been due to a head wind and/or low tire pressure if you haven't been adding air as the days have cooled.

4. It's also possible that the sea foam messed up an O2 sensor.


I wouldn't stress. Give it a couple of tanks and see what happens. To be on the totally safe side, you could take it in and see if they can read any codes.

 

I give up. Why ask questions when you already know the answer? It's not the gas the end.