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Fuel efficiency

You will have no problems with bosch sensors, they make a great product. Anything that meets oem specs will work, they just may not last as long as motorcraft. If you haven't been keeping up on fluid changes, that is absolutely an area you will pick up some fuel efficiency. I assume you regularly change engine oil, but change the tranny/tansfer case fluid, front and rear diff, and it wouldn't hurt to change your power steering fluid. Also something that might have been missed. If you have 4x4, make sure your hubs are unlocking.

It's not 4x4 so I don't have that issue. But, I will be looking at the rear differential. I've never changed this fluid before in a vehicle. Is there a guide or best practice on how to do it? How do you know if there is enough or the right amount?

Also, what's the proper viscosity for this truck's rear end?
 



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75W 140 SYNTHETIC ONLY. with limited slip modifier.

It's full when gear oil spills out the filler hole.

I recommend this stuff:

It's best to pull the cover off and give it a cleaning with a little carb cleaner and wipe out the sludge. A new gasket will be required. (cheap and readily available) Red RTV silicone for gasket goop. Just a light coat, no need to get carried away glop'n RTV on. (more is NOT better)

45006_zpsabbqakgl.jpg
 






No CEL and sudden drop in fuel econ = bad ICM (Ignition Control module)

The ICM on these has a fail-safe circuit. "limp mode"

It will run fine even pass emissions, but suck the gas.

The ICM fail will not produce a CEL.

The only fault at the ICM that will produce a CEL is a bad ground. Which is misleading as it shows as a crank position sensor fault.

It is located in front of the battery on the core support. Not a good location, vibration and corrosion prone area.

I have sealed mine in a water tight box and mounted it on rubber vibration isolaters.
 












75W 140 SYNTHETIC ONLY. with limited slip modifier.

It's full when gear oil spills out the filler hole.

I recommend this stuff:

It's best to pull the cover off and give it a cleaning with a little carb cleaner and wipe out the sludge. A new gasket will be required. (cheap and readily available) Red RTV silicone for gasket goop. Just a light coat, no need to get carried away glop'n RTV on. (more is NOT better)

45006_zpsabbqakgl.jpg

Is one bottle enough to fill it?
 






No CEL and sudden drop in fuel econ = bad ICM (Ignition Control module)

The ICM on these has a fail-safe circuit. "limp mode"

It will run fine even pass emissions, but suck the gas.

The ICM fail will not produce a CEL.

The only fault at the ICM that will produce a CEL is a bad ground. Which is misleading as it shows as a crank position sensor fault.

It is located in front of the battery on the core support. Not a good location, vibration and corrosion prone area.

I have sealed mine in a water tight box and mounted it on rubber vibration isolaters.

Is there any way to test this piece before throwing $180 at it? Also, is it one of those parts that I really should invest in the Motorcraft version vs. the Standard Motors on at $60 cheaper?
 






Is one bottle enough to fill it?

No, I used almost 2 on the front diff, although that was with some spillage. The rear, I think, takes more. I'd be tempted to get 4 quarts to do front & rear, that SHOULD be enough.

The frustrating thing is, the manual gives 3 different volumes; US Imperial, Imperial and Metric. If you run each number through a converter, it'll give you different volumes. I never found a 100% straightforward answer aside from 'about' or 'approximately'.

I also did a lot of research and unless you plan to tow or heavily offroad, you can stick to 75W-90. The 75W-140 synthetic approaches double the price. The manuals recommend a 80w-90 conventional oil for front & rear. The 140 stuff could hurt fuel economy since, when warm, it's much thicker. Some people swear by Royal Purple or Amsoil, personally, I'd stick with Valvoline or Mobil 1. I try to stay away from the Walmart or other re-bottled stuff (auto parts stores) since you don't always know what it is. I picked up 3 bottles of Mobil 1 75W-90 Synthetic for $7.20 per quart shipped at Advance Auto Parts with a coupon, cheap.

As FR-425 said, put the Motorcraft limited slip additive in if you have a D4 rear. Even if you get gear oil that is rated for limited slip, put it in. It's not that expensive and it saves you hassle down the road.


*EDIT*
As for the ICM, that should probably be your last effort. Places like RockAuto or Advance Auto Parts likely have it for cheaper and you can easily find coupons for them.

When the ICM goes into limp mode, does that mean that the timing is no longer computer controlled and set at the default 10 degrees BTDC? If so, you could either check the timing with a light (hard to do since there's very little in terms of reference marks) or yank the SPOUT connector and see if your MPG changes. If my theory is correct, when you pull the SPOUT connector, that will make timing go to 10 BTDC and should hurt your gas mileage. If it doesn't, then you know that the computer isn't advancing the timing at all (with the SPOUT) and something is wrong.
 












Is that the "Friction modifier": http://smile.amazon.com/dp/B000NU5LP6 ?

That's the stuff.

Beware, it smells HORRIBLE. I bought 2 bottles (doing a flush) and even sealed with the vacuumed foil on top and the cap tight, the smell still gets out and on warm days, it stinks up the room.

Anyway, I don't recall seeing it anywhere, do you actually have a limited slip rear? If not, you don't need the additive.
 












Negative on the additive! The Royal purple already has the friction modifier in it.

In fact most synthetics have it. No point in spending the money for gear oil without it and then buying the additive separate.

Do NOT add friction mod to gear oil that already has it. (again more is NOT better)

In the case of the 8.8 synthetic gear oil is required because of the type of seal material, conventional oil will deteriorate the axle seals. And if you do have the limited slip your in real trouble. If your not sure best to assume it is.

If the tag is still on the diff it will have 3LS73 stamped on it. 3.73 being the gear ratio. If it's a 4.11 ratio it would read 4LS11 etc. No LS = open diff, still need synthetic though.

Perhaps that was not the case for first year Ex's but it is certainly true for 93' & 94' synthetic verses conventional oil that is.




The 8.8 holds 2 & 3/4 so three bottles are needed.
 






I think your going to spend a lot more messing around with other stuff, o2 sensors for example.

You have no CEL, so you have no emissions control related failure. It's just that simple.

A failed ICM will not cause an emissions related issue and therefor is/was not required to be monitored back before OBDII.

If no CEL you can eliminate EGR, o2's, vapor canister, cam sycro, etc.

If you had a vacuum leak = CEL - lean condition.

Leaky fuel injector - CEL - rich condition.

Runs ok, NO Check engine light, really poor gas mileage = ICM.

If you had any other symptoms, rough idle, stalling, CEL, anything, I would not feel so sure about my diagnosis of bad ICM.
 






I think your going to spend a lot more messing around with other stuff, o2 sensors for example.

You have no CEL, so you have no emissions control related failure. It's just that simple.

A failed ICM will not cause an emissions related issue and therefor is/was not required to be monitored back before OBDII.

If no CEL you can eliminate EGR, o2's, vapor canister, cam sycro, etc.

If you had a vacuum leak = CEL - lean condition.

Leaky fuel injector - CEL - rich condition.

Runs ok, NO Check engine light, really poor gas mileage = ICM.

If you had any other symptoms, rough idle, stalling, CEL, anything, I would not feel so sure about my diagnosis of bad ICM.

Thanks, FR. I guess I'll put one on order, then and send back the O2 sensors. That's half the cost of the ICM anyway... so helps to mitigate the cost to some degree.

The truck IS 22 years old now, so it makes sense that many of the original parts would simply be going out over time. I've had it about 8 months now, and it's been generally reliable once I replaced the PCM (first thing to get it daily driver friendly, and also successfully troubleshot based on input by you). This fuel efficiency thing just didn't make sense to me.

Everyone's input is appreciated.
 






I just did my rear differential a couple of months ago. Here is a link that I followed.

http://www.explorerforum.com/forums/showthread.php?t=214805

If you backup on this link you will find that this page has all kinds of do it your self maintenance/repairs. And these guys on this forum have great advice. They helped me thru a head gasket repair which I never thought I could even attempt.

So, doing this differential fluid change out is doable. It was very easy with regular hand tools. The only possible difficult part may be the fill plug access in the rear differential which faces towards the front of the vehicle. And you may have to spray PB blaster on it to loosen it. It requires an hexagonal or allen point to remove. Take your time.
 






I would like to chime in on the diff fluid. There is no reason to go anything other than full synthetic here. I would actually go 75w-90. Friction modifier is in nearly every synthetic gear lube. You will get better gas mileage with the 90, and there is no reason for the 140. The manual calls for the 90 unless you do a lot of heavy towing. I use ultra black RTV (not regular black) for the gasket. Its a very simple job to do, it just takes a while for the RTV to seal. Just break the fill plug loose, unbolt the pan and pop it off. Let the fluid drain, and clean up the surfaces to seal. Run a continuous bead of RTV on the pan in the groove, and carefully put it back on the diff. I like to use two hands and get it straight, then thread in some bolts. Hand tighten the bolts where the RTV is just starting to squish. After about 24 hours, finally torque the bolts down (I think its 30-35 ftlbs). Then take the fill plug out and fill until fluid comes out.

For the tranny I feel what you use for fluid is not as important as changing it regularly (every 30k to 50k). You can get a gallon of Valvoline full synthetic for $16 which is what I do. The m5od is easy. you unbolt the drain and fill plugs, and let it drain. Then you put in the drain plug, and fill it until the fluid comes out the fill plug. I like to use a pump (its like a giant syringe), but I've seen people rig up long tubes and let gravity work, or you can even pop off the shifter and fill it there. On the a4ld you need a tranny pan gasket and filter. You unbolt about half the bolts and just break the others free. Then slowly separate the unbolted side and try to catch the fluid. After that, unbolt it all the way, and dump the rest of the fluid out. You will only ever get about a third of the total fluid this way. If you really want to, do this twice after driving it to get most of the old stuff out. Flushing is not necessary, and can cause damage. Anyway, the filter can just pop off, and put the new one in. Put the new gasket on the pan, and align it on the tranny. I dont remember the torque for those bolts. Then fill it through the dip stick tube.

Also don't forget about the transfer case. It takes the same tranny fluid. First you remove that counter balance on the back. Then you can see both the fill and drain plugs. Take both out, and once its drained, put the drain plug back in. Then fill until it comes out the fill plug. Finally put the counter balance back on.

I think both trannys take about 3 quarts to fill.
The transfer case was about 1.5 quarts.
The rear diff takes about 3 quarts as well.
 






The thing about the additive already in the bottle is that there's no specification that is being followed on the bottle. How do you know how much is in there or if it's the right type of modifier?

There's many different ways you can think about it. But to me, Ford made the axles, Ford made the friction modifier. Maybe you don't put the whole bottle in, maybe just half and see how it goes. They say it's only for noise reduction but excessive noise & heat are often associated with premature wear. I'm running 80w-90 conventional right now with a whole bottle of friction modifier and it behaves perfectly. Lays down 2 tracks in the snow and I've never heard a peep out of it.

To touch on the whole 75W-140 vs 75w-90 thing again, at some point, Ford did switch their recommendation for the 8.8 to 75W-140 synthetic but I'm not sure when. I know in my 1991 manual, they state 80w-90 conventional. Because of that and the fact that I won't tow, haul or do hard offroading, drive 80MPH for long periods and that I'm in a cooler climate, I'm sticking with 75W-90. Now, if you intend to use your Explorer a bit harder or you drive long distances in the southern states, you might consider the 140.

The synthetic, especially being 20+ years newer than the vehicle, will provide more protection than the fluids that were formulated at the time. That said, it all depends on what you're going to do.

One thing I came across a lot when researching is the comments from people who find old Ford 8.8's from muscle cars in the 70's & 80's at junkyards is that how impeccably clean and new they look inside. In 50 years, if there's one thing left that works on your Explorer, it'll probably be the rear axle. My point is, pretty much any gear lube you throw in there will do the job. The fact that you're even wanting to change the fluid at all is the best thing you could do for it. What you put in doesn't matter nearly as much as changing it. If you want to spring for something that has more protection, there's nothing wrong with that. Just don't beat yourself up researching or worrying if you made the right choice. It'll be fine as long as the bottle says 'gear oil'.
 






I should do mine...I KNOW it hasn't been changed in 22 years.....
 






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