This Outland Engineering leveling guide will show you the fastest way how to level your Outland Engineering skill up from 1 to 75 as inexpensively as possible.
Engineering is the best combined with mining. I highly recommend leveling these professions together because it will be a lot easier to get the needed materials if you have mining. Often the materials are based on a case that you will gain one skill point for each craft. This won't happen, so you will have to get a few extra materials while you are leveling Outland Engineering.
Approximate Materials Required
The guide uses a lot of yellow and green recipes, so it's very hard to tell how many materials you will need exactly.
- 300-450x
Fel Iron Bar - 40x
Mote of Earth - 20x
Mote of Fire - 35-45x
Primal Earth - 70x
Netherweave Cloth - 200-350x
Adamantite Bar - 6-15x
Primal Fire - 6-15x
Khorium Bar
Engineering Tools
You will need some kind of tool to craft most engineering items. These tools are:
Blacksmith Hammer - Sold by Engineering or Blacksmith supply vendor.
Arclight Spanner - Requires 50 skill in Vanilla Engineering to craft.
Gyromatic Micro-Adjustor - Requires 175 skill in Vanilla Engineering to craft.
I highly recommend getting a Gnomish Army Knife to save some bag space. It replaces all of these tools, so you only have to carry one item with you.
The Gnomish Army Knife also replaces 
Jeweler's Kit, 
Virtuoso Inking Set, 
Runed Copper Rod, so if you have any of these in your inventory, you can throw it out.
Where to get The Gnomish Army Knife
-
You can buy the
Ultimate Gnomish Army Knife from the Auction House. -
If you already learned Draenor engineering, you can craft one
Ultimate Gnomish Army Knife for 5 
Gearspring Parts. (Craft one Gearspring Parts for 15 x True Iron Ore, 15 x Blackrock Ore. It will actually create 8 Gearspring Parts). -
You can also craft
Gnomish Army Knife if you have Northrend Engineering, but it's usually more expensive to make or buy.
Engineering Trainers
You can learn Outland Engineering from Engineer Sinbei in Shattrath City.
If you choose the Aldor faction during one of the Outland quests (or you are Draenei), then you can't interact with this trainer, you have to visit Technician Mihila in Shattrath City to learn Outland Engineering from her.
Racial Bonuses
Gnome characters have +15 Engineering skill because of their passive 
Engineering Specialization, and Kul Tiran characters have +5 from the trait 
Jack of All Trades.
Any extra Engineering skill means recipes stay orange for more points. You can save a lot of gold by doing lower-level recipes for 15 or 5 more points.
Leveling Outland Engineering
1 - 20
You will use all of these later, so make them now for free skill points.
- 126 x
[Handful of Fel Iron Bolts] - 126 Fel Iron Bar - 20 x
[Elemental Blasting Powder] - 40 Mote of Earth, 20 Mote of Fire - 56 x
[Fel Iron Casing] - 168 Fel Iron Bar
20 - 25
5 x 
[Fel Iron Bomb] - 5 Fel Iron Casing, 10 Handful of Fel Iron Bolts, 5 Elemental Blasting Powder
You might need to make more than 5 of these if you are unlucky with the skill point gains.
25 - 35
34 x 
[Adamantite Frame] - 136 Adamantite Bar, 34 Primal Earth
You will use all of these later but you can stop making them when you reach 35, and make more later.
35 - 55
70 x 
[White Smoke Flare] - 70 Netherweave Cloth, 70 Elemental Blasting Powder
This will be green for the most part, so this is just an approximate number.
The recipe is sold by these vendors. If you are in Shattrath City, then Wind Trader Lathrai is the closest one. It's a limited supply item, so if someone bought it before you, then you have to wait for it to respawn or go check the other NPCs who sell the recipe.
55 - 60
6 x 
[Khorium Power Core] - 6 Khorium Bar, 6 Primal Fire
It's not required to reach 60 with these, you can go to the next recipe.
You will probably need to make more than 6 of these later on, but you might get lucky and gain skill point almost every single time between 70-75, so 6 is a safe number. I personally always had to make at least 7 Field Repair Bot 110G at the 70-75 part, and 13 was the most with unlucky skill gains.
You will need these later! There isn't a single recipe between 70-75 that doesn't use [Khorium Power Core]. You will have to use some 
[Khorium Ore] no matter what, so it's better to make them now for a few "free" skill points.
60 - 70
Khorium Ore is usually so expensive at most realms that it's just better to make Adamantite Rifle until it turns grey, but if you have a lot of Khorium Ore, then you should make 3-4 more Khorium Power Core, and stop making Adamantite Rifle at around 67 then switch to the Repair Bot.
17 x 
[Adamantite Rifle] - 51 Fel Iron Casing, 34 Adamantite Frame, 68 Handful of Fel Iron Bolts
You will probably need to make more from these. It's usually between 17-23.
The recipe is sold by these NPCs. If you are in Shattrath City, then Viggz Shinesparked is the closest one. It's a limited supply item, so if someone bought it before you, then you have to wait for it to respawn or go check the other NPCs who sell the recipe.
70 - 75
6 x 
[Field Repair Bot 110G] - 6 Khorium Power Core, 48 Handful of Fel Iron Bolts, 48 Adamantite Bar
You will most likely have to make more than 6 because the recipe will be green for the last 3 points.
[Schematic: Field Repair Bot 110G] is dropped by Gan'arg Analyzer in Blade's Edge Mountain. There are 4 groups of these mobs, but there are around 4-5 minutes between respawns after attacking the first group. The drop chance is pretty high, you will probably get it after you clear the 4 groups the first time.
WARNING: The recipe won't drop twice, so make sure you don't already have it in your bank!
Note: Not sure why but wowhead lists the NPC as named Simon Unit, in-game the NPCs are called Gan'arg Analyzer.
I hope you liked this Outland Engineering leveling guide, congratulations on reaching 75!