Sudden drop in MPG on the Al-Can

I’m currently driving my 98 v6 Tacoma to Alaska and have been having fuel economy issues since the second day. This truck usually gets anywhere from 20-24mpg

day one drove ~320 miles to Denver, co and got about 21mpg

the following morning it was raining HARD for quite a while then stayed super windy in Wyoming. That morning had to fill up with a fuel light on at 240ish. 17.3 mpg.

since then it has remained in the 17s slowly lowing into the 16s. I’m now 2000 miles in and my mpg is dropping just topped off before stopping for the night and it’s down to 15 with a tiny bit of snow on the ground and 15 miles or so in 4x4. I thought it may be because of the violent wind in Wyoming, Montana and Alberta combined with my roof box and all the added weight of my gear. But why is it getting worse?


I’ve done a bunch of research already on this site and others and haven’t found an answer. Obviously. So far I have added sea foam to the tank, lubed the u joints and replaced the air filter. Plugs and wires done about 5k ago. Tranny and dif oil 3k ago. I’m running fresh synthetic motor oil. All the wheel bearings sound normal. Tire pressure is fine. Alignment is slightly off but has been for a while. There is no cat in the exhaust. The only thing I haven’t done is o2 sensor.


So if the o2 sensor doesn’t work why the sudden drop in mpg? It’s a little concerning as gas here is really expensive and far apart and cell service will only get worse the further up the road I get.

I write this while waiting out a blizzard in BC before continuing tomorrow. Just hoping for some enlightenment

 

Shitty gas. When i did my interstate travels CA, NV, AZ, UT, WY, ID, OR and WA. There is poor quality gasoline at some has stations due to weather factors and luck.

 

that thought crossed my mind but how did I get unlucky 12? Or so times on one trip when that has only happened to me a handful of times in the past

 

Are you front Denver? Is your truck tuned for higher elevation or something? As you lower elevation your air density goes up... you'd think you'd be running leaner, but that could result in poorer fuel economy.

 

Colder climates run higher ethanol contents. Looks like youre from New Mexico? As you travel more north there will be higher ethanol content which will drop MPG. Also you'll be running up more grades as you travel north. The PNW has lots of mild grades which can suck MPG but can be hard to notice. Also, colder weather uses more gas. Different traffic patterns like driving slower or faster than normal will also effect MPGs.

 

Yeah
Can’t even buy 93octane in CO
I’m sure the same as pacific NW states

maybe dump some of that Octane boost in and see if there is a MPG change

 

I have never gotten better milage as the temps drop.

The hotter the weather, the better the mpg.

My theory is the delta T for combustion. It's less when it's hotter. Equals better mpg.

 

Colder air is more dense which means more oxygen so if the air charge volume stays the same but there's more oxygen more fuel is required to achieve the same AFR. Hense less mpgs.

 

Agreed

in fact we(my trivia team) had similar Q
(We got wrong)

A car gets better MPG with winter blend or summer blend gasoline?

Summer blend was correct answer

 

My Az truck has never done better than 16mpg

 

There are a couple of things that I can think of to check, monitor the change in barometric pressure and see if it changes with altitude and your long term fuel trims. Quick and easy, check your air filter.

 

This was happening to me, turned out my front calipers were heavily dragging. Seems to be a common issue with older 1st gens.

I had no squeaks, smells nothing. I only found it when I went to rotate the tires, I could barely spin the wheels the brakes were so tight.

OEM calipers were a little too expensive, so I slapped on some premium NAPA calipers.

 

NM has high ethanol content, that's not his issue.

 

Idk much about the elevation change on your route, but as mentioned, grading will have a significant play, as will added wind resistance (you mentioned it was windy but not what direction)

 

I've read of people picking up a mpg or two by cleaning a MAF.

 

I've sold fuel additives and heard a lot about the results, and someone mentioned bad gas and it may well be that. Most bad gas is moisture and I've seen pretty good results from HEET.

There are calipers with (plastic) phenolic pistons and steel pistons. Pay the extra for the steel pistons if you find a caliper is sticking. Phenolic pistons have a history of wearing unevenly and eventually binding because they no longer retract.

 

Over the years I've seen a lot of calipers start to stick due to old brake fluid(black).
Brake fluid is hydroscopic and eventually corrodes the pistons. (Steel caliper pistons)
Here in wet PNW I try to flush my brake fluid every year or two.
If it looks dark it has absorbed water.

 

Barometric pressure... Some manufacturers read the barometric pressures once, on start up. If you start your motor at sea level and then drive up a mountain the barometric reading is still at sea level when you are at say 5000 feet. The tables that the PCM uses to make calculations is throw out the window and the spark, fuel injection etc are now not calculted but fixed. Does Toyota programing for your year make and model check the barometric pressure constantly, I dont know, thats why I asked it to be monitored. If it is checked continuosly then this isnt the problem.

All of this discussion assumes that the simple things like tire pressures, alignment etc are OK. Weird things happen on the road, a buddy of mine had the threaded sleeve that adjusts the toe on his 3/4 ton truck slip after a series of pot holes. I told him he is lucky that it pressed together rather than pull apart as he was in the middle of no where in AZ gold prospecting. His MPG went into the toilet when he got on the pavement and drove the 75 miles to town. One adjuster sleeve one tire and an alignment, almost $500.

 

I vote dragging brakes. Front, rear or parking.

 

if it is dragging front brakes in particular are there any other symptoms that would be noticeable, prevalent, out of the ordinary?
perhaps noticeable uneven pad wear on one side vs the other side?


how about issues with the fuel pump?