2005 Honda Accord Hybrid. 108,000 miles. I changed oil and filter last week. 4.5 quarts 5W-20 Super Tech High Mileage Full Synthetic. NAPA 7356 Gold filter. Car feels OK. But since changing the oil, when I start from cold, reads 5 mpg on dashboard display, slowly creeps up, finally reaches about 26 after 5-10 miles. Never did that before. Previously always 26 mpg from the start. No OBD codes stored. When I run car for many miles, turn off, start up hot, starts at 26 mpg. Seems like something is warming up, and then the mpg is OK. Transmission fluid seems fine. I have some left-over new oil, the prime suspect, and it seems to flow fine, but I don't really know. Any suggestions? Any additional info I might provide? Thanks

 

Just wanted to add that I have owned this car over 5 years, it never had this behavior before the recent oil change. Daniel

 

Does your oil fill cap or owner's manual recommend to use 5w-20 motor oil?

 

Thanks for asking. Yes, both the fill cap and the owner's manual recommend 5w-20 motor oil. And I have always used 5w-20 before. BTW, I am in Seattle. Temperature is 40-50 F. Not really cold where the oil might get sludgy. I could change the oil again with a different brand, but that sounds like total guessing, kind of stupid. It would be much better to understand what is going on. Maybe I could buy some more oil (different brand) for future use, and somehow compare the viscosity with the remnant (about 2 cups) of the Super Tech I put in the car. But I already looked at the remnant, and it seems to flow quickly when I pour it, similar to my memory of how oil flows. I doubt the filter is at fault, because why would it perform better after warming up? I think the mpg indicator is OK, no reason to believe not working correctly, and problem started immediately after changing oil. I'm stumped, and hoping for additional suggestion from someone.

 

The engine computer keeps the mixture rich until the engine warms up to operating temperature, so the oil should have nothing to do with the initial drop in mpg.

Have you always watched the mpg on your vehicle? Just wondering if you never noticed the low mpg when the car is warming up.

Keep an eye on your coolant temperature gauge to see if it takes a while to reach operating temperature. If you have the ability to read live data, you could look to find out when the car goes into closed loop. That is where the O2 sensors are warmed up and take over the amount of fuel being added. I think the coolant temperature also factors into the car going into closed loop.

You should scan for engine codes just to be thorough. Most parts stores do this as a free service.

Was any other work done on your car recently?

 

Thanks for the questions and suggestions.

"the oil should have nothing to do with initial drop in mpg" - Makes sense. If I knew that for sure, I could focus my diagnostic efforts on other causes, and forget about the oil. But problem first started after oil change, so I suspect the oil.

"always watched the mpg?" - Yes, I normally watch the indicators. I think I would have noticed low mpg if it happened before. It's not just a few seconds. The car must be driven 5-10 miles (10-20 minutes) before the mpg creeps up close to normal. I'm sure this is a new problem.

"Keep an eye on coolant temp gauge" - It seems to function normally. Gradually rises to middle of dial.

"read live data" - I believe I can, and might try that, if I can figure out how to tell "open vs closed loop" from the data.

"open loop / closed loop" - I didn't know about that. It does relate to warming up. However, the mpg *gradually* creeps up. If low mpg is caused by switch from open to closed loop occurring late, I would think the change (to normal mpg) would happen relatively quickly, when the switch happened. Does switch from open to closed loop happen at once, or gradually? About how long car should stay in open loop? Anybody know if open loop is associated with very low (5 mpg) fuel economy?

"scan for engine codes" - As previously mentioned, I scanned repeatedly. I have an OBD2 reader, am adept at using it, previously diagnosed and fixed problems with it. No pending or stored engine codes.

"any other work done?" - No work for over a year. Car has been very stable.

 

Almost as if the MPG indicator formerly indicated average MPG over some time prior to engine starting. But now it resets and shows the initial low MPG because it isn't averaged with the last few drives. I don't know the MPG display behavior well enough to know if that's a different mode of averaging? Or whether there's some buried setting that displays MPG averaged only since the last startup?

Switching to closed loop is a sudden event, but the cold-start-enrichment gradually tapers off while engine warms up. The switch to closed-loop happens pretty early because I think the O2 sensor heater brings it up to temperature within a minute. The engine oil and the intake manifold are still pretty cool when it switches over.

I wouldn't really suspect the oil - I've even read that brand of oil isn't too bad. I might suspect the averaging method switching to something different if you had disconnected the battery or something like that.

 

When was the last time the battery was checked. You have the Hybrid so I don't know how your MPGs work. I have the EXL w Navi and mine started acting up due to the battery along with my display in the dash. Once I changed it everything went back to normal. I tried everything since my battery was only 2 years old (grounds, alternator, even thought it was the Navi itself)

 

"I wouldn't suspect the oil" - That's reassuring to hear again. The oil looks and flows fine. The car seems to run OK.

"Last time battery was checked?" - IMA battery under the seat has never been checked, but I think it is OK: charge bars light up regularly, ECO frequently lights up, IMA indicator comes on only when starting, and "Auto Idle Stop" most stops. I believe 9V battery in front is fine, I will double check voltage tomorrow.

"MPG indicator formerly indicated average MPG" - I thought the mpg indicator showed *current* mpg. Thanks for correcting my wrong idea. Yes, the manual says it shows "average fuel mileage during the trip, updated every 10 seconds". It seems (to me) more useful to know the current real-time mpg, that's what I thought was being displayed, and it seemed like current mpg (see below).

"the averaging method switching if you disconnected the battery" - I *do* regularly disconnect the battery. [[[ I have an old post from years ago concerning a parasitic drain, 1 amp x 90 minutes every time I stop the car, that never got resolved. I traced the circuit as far as I could, and it was easier to disconnect battery than to buy and replace computer component, with no assurance it would fix problem. Please note that I am not expecting feedback on the parasitic drain, I'll post separately if I continue that work. ]]] But the manual does not mention different averaging methods, so my guess is the mpg meter operates only one way.

"what is a trip?" ("average fuel mileage during the trip") - This matters. Every time the battery is disconnected, the trip meters are reset, so a new mpg average is started up. That's nothing new. But in the past, after reconnecting battery on the cold car, it started at a reasonable mpg (not super-low like 5), did not stay low for many miles, creeping up slowly.

Of course, I cannot prove old behavior, I don't have a video or picture. There *is* a possibility I just never noticed before. Any chance someone has a 2005-2007 Accord Hybrid to check if it starts at super-low mpg when starting new "trip"?

I have learned a lot from the forum. Let me do some experiments the next few times I drive, and then get back with the results. For example:

1) If I drive a lot, stop, disconnect / reconnect battery, then drive some more, does it start at 5 mpg or 26 mpg? If 5 mpg, that rules out oil as the problem, since oil is hot at that point. Not sure what else is proven by the test...

2) If my OBD2 reader allows the test, when does it switch to closed loop from cold start? If several minutes, that indicates problem with something like the O2 sensor. If less than one minute, sensors are OK.

3) I filled the gas a few days ago, and wrote down the mileage. After I have driven enough to refill the gas, what is the actual mpg (miles driven / gallons added)? If 25 to 30, that indicates that everything is OK, and that maybe this is *not* a new behavior, despite my strong belief that this never happened before.

4) Double check 9V battery, just in case.

If any other suggested tests or thoughts, let me know. Otherwise, I'll post to the thread again after getting results. Thanks

 

Here's where I demonstrate how ignorant I am about the hybrid...

What's the 9v battery? Without knowing anything, I expected a "normal" car battery up front because why would anyone bother to invent ALL NEW components to operate at a different voltage. I expected the IMA battery to be unrelated to this stuff, only operating within the driveline for the motor/generator.

Certainly check the 9v battery if it does all the electronics etc. Maybe you can devise a load-test? Batteries often can show full voltage with a DMM because it doesn't draw any real power.