You said you have 60,800 miles now, and had the oil changed at 60,000. That's about 2 tank of gas over the miles you changed the oil. I'd still start there at the beginning of your drop in MPG. Something changed after the oil change according to your miles. It could also be your A/C has a slow leak and the HV battery is hotter and restricts "Assist". These are starting points to check out that will not show up as a code.

Did you check the oil on a flat surface? Who did the oil change? Was it done on a flat surface? You don't have to have smoke to notice a drop in MPG, I didn't in my '09 FEH.

The dealer tech should never tell you to add any gas treatment for cleaning cylinder carbon, check the manual for additives.

Need more info.

Gary

 

Gary, Using exactly the same logic as you (after I read all the posts in this thread) I was SURE that my low mileage problem started immediately after the last oil change (done at the dealer, btw), which was about 3 tanks of gas ago.. I immediately checked my oil level an a completely flat surface, and was disappointed that it was near the low mark since I was SURE that would be the problem. Yes, the engine was warm, and yes, I waited 15-30 minutes for all the oil to drain to the pan. The dealer's "quick lane" oil change area is also flat, and they use a 4-wheel full vehicle lift to elevate the car to drain the oil. Slow leak on the A/C is possible, but it puts out COLD air in our 95+ degree heat here. Plus, shouldn't any high heat condition in the HV battery (sufficient to restrict battery assist) generate one of their precious error codes?

I agree that the dealer should never recommend gas treatment. I figured they were grasping since I (THE CUSTOMER) was sure he had a problem but their diagnostics told them I didn't.

I also agree with you that SOMETHING had to change about 800 miles ago because the mgp drop was sudden and huge. Don't know where to go from here, except check the mileage on this next tank and report back.

Again, I appreciate your thoughts!

John

 

Since you bought this '09 FEH new, can you give me your VIN number?

Gary

 

Gary, Sure. It's 1FMCU59359KA85524

Just curious: what does the VIN tell you?

 

The VIN number lets me know that you're not a spammer and have a real problem. I know now you're not wasting this board's time. BTW, here is a copy of your window sticker:http://services.forddirect.fordvehic...CU59359KA85524 Anyone that wants a copy of their VIN, just change your VIN in this link.

The battery aux A/C can have problems and not show any codes. My A/C had a leak and I found no codes and neither did the dealer. My leak drained everything including the oil in the system and the dealer charged the system back and never found the leak to this day.

It sounds like the problem is not your engine, but the problem with Assist could be. This suggest overheating of the hybrid system which makes your engine work harder and decreases MPG. If it is, the problem will get worse before it gets better in your weather. Driving a longer trip till you get a "Stop Safely Now" warning will set the code you need to find the problem. Members here send me a Private Message all the time when they get this message on a long trip. I advise them to let the system cool down and proceed at a very slow drive to a Ford dealer. A Problem with the A/C will not give you a message, but only stop Assist as part of the fail safe system in your FEH.

Gary

 

Gary,

Thank you again. I assure you I'm no spammer, but I guess you've figured that out. (Do you get that a lot? Sheesh!)

I've read through your last response twice. Forgive, please, my ignorance, but are you saying I have an aux A/C that's just for the HV battery cooling? And that it can fail or malfunction and not produce an error code?

If all that be true, is there any way I can determine if this is my problem (rather than wait for the "stop safely now" warning -- never seen that!)? I'd love to go back to me dealer and tell them (teach them) what the problem is!

John

P.S. You mentioned that members would send you a Private Message. Should I do that and get this traffic off the forum? I didn't know I had that option.

 

No need to PM me, I prefer people to post to the group so all can learn.

There is a separate aux A/C for the battery, but there is only one belt driven compressor for both the cabin and the battery. You have no control of the battery A/C. This means you can shut off the cabin A/C, but the compressor with continue to operate when the battery needs cooling. The ideal battery temperature is 78F, so if your outside temperature is higher, chances are your compressor is running to cool the battery. As I said, you may never get an error code or "Stop Safely Now" message if the aux A/C is not cooling enough. The hybrid system is protected by the fail safe system from getting to hot by shutting down or restricting Assist and EV. The internal battery fans will give you codes when they stop working.

People have felt the coolant lines to the aux A/C to see if the line are cold, but how cold is cold enough?

Do you know you have a battery air filter that needs changing at least every 20,000 miles?

Gary

 

Gary,

Okay, several things here. Yes, I knew about the HV battery vent/fan system and associated air filter. I just checked that filter this morning (although it HAS been changed in the past) and found it properly installed and clean. No apparent problem there.

Next, in January of this year I did have a cabin A/C problem (no cooling). The dealer found a leaking line (9M6Z*19835*D Tube Assembly -- $249.88), replaced it and evacuated and recharged the system. Since then it has been cooling the cabin just fine. To be honest, I don't know exactly when my mileage first started to deteriorate, but it's been really dramatic for the last two tanks of gas. Maybe my problem started then (January) and just got really bad in the summer heat?

Next, I assume the single A/C compressor uses the same refrigerant for both battery cooling and cabin cooling? In other words, it's all one system but with two different evaporator coils; one for the cabin and one for the HV battery? If so, I KNOW the compressor and cabin evaporator and blower are working great. So if the battery is not getting cooled, the problem would have to be the blower for the battery (airflow across the cooling coils in the battery area), right?

I'll gladly crawl under the car when it's hot and feel those lines running back to the rear (I just noticed them recently and wondered what they were!) to see if they are different temps, one hot/warm and the other cold/cool. If that's my finding, I'll have eliminated the battery A/C system as the problem. I think. As you ask rhetorically, how cold is cold enough?

John

 

John, if the fans are not working, there would be codes and more serious problems than reduced Assist and MPG. The amount of charge and a weak or worn compressor could be the problem. It has been posted that a weak compressor has problems cooling both systems. You might try driving in the morning without the cabin A/C and compare Assist mode after warm-up. Then reset your MPG average to see if your MPG increases. You can check your assist mode first, then turn on the cabin A/C and test MPG while the battery is still cool from the aux A/C.

If everything is good, we can go to possible other problems. And yes, you understand both systems now.

Gary

 

I forgot John, I had a dying 12V battery that caused a decrease in MPG. That would not effect Assist though. After I changed the battery, MPG went back to normal.

Gary