Adventure Driven Talk

Tech Questions and How-To Articles => Mitsubishi Related => Gen 2 Montero => Topic started by: toby088 on October 14, 2018, 01:24:14 PM

Title: 10 mpg in a 1996 Montero SR?
Post by: toby088 on October 14, 2018, 01:24:14 PM
Just picked up a 1996 SR and my first tank and a half through it returned just a hair over 10mpg. I definitely didn't buy this thing for the mileage, but 10 seems super less than I've gotten in a 1-ton Ford truck with a 460. Has around 120k miles and aside from a really slight rough idle it runs great. Im going to get it up in the air and check for a dragging brake or bearing, but it runs straight and quiet down the road. Tires are inflated properly, everything seems normal. This has been primarily city driving and I have been running it on premium as the filler lid says to do. Is 10mpg normal for this thing?
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: Crumb on October 14, 2018, 04:10:18 PM
I get a pretty consistent 15mpg and i have 35" tires, mine is a 99 with SOHC engine so a 96SR might get 1mpg less with the same tires and proper gearing. You should see 17mpg maybe better depending on driving style.
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: Shovel on October 14, 2018, 07:10:48 PM
10 is way out of ordinary. 

How far from stock is your Montero?  How's the power?  What maintenance has been done?  How does the transmission shift? Where does the temperature needle sit when warmed up?  Any lamps on in the dash?

Title: Re: 10 mpg in a 1996 Montero SR?
Post by: toby088 on October 14, 2018, 07:53:45 PM
Its bone stock, aside from having a set of 31's on it. No lights on dashboard, and OBDII reader doesn't show any incomplete monitors.  Only issue with the trans is that when I'm starting out cold, it will not want to shift out of 1st gear for the first 2-3 minutes of driving. It will upshift, but only after the RPM is significantly higher than the normal shift point. After those first few minutes it shifts perfectly through all gears, including OD. If anything I feel like it could downshift a little sooner, but its nothing out of the ordinary.

Temp needle sits right in the middle of the range when warm.

I've never driven another Montero to compare the power with, but honestly it seems a little less powerful than I'd have expected. My other car is a 1969 Baja Bug (stock single port 1600) so like...kinda apples and oranges, but on this one long sweeping grade near my house I can keep the bug at like 47mpg in 3rd with the pedal pretty far down. On the same grade, the Montero could only hold about 57 with O/D off and the pedal pretty close to floored. In normal conditions though the power feels...adequate to me?

Unfortunately maintenance is a bit of an unknown - PO said it had all been kept up on but he didn't have the paperwork. I'm at a point in my life where a few extra bucks is worth piece of mind, so I bought OEM timing belt, water pump, pulleys and tensioner, spark plugs, associated gaskets, and will be ordering a crank pulley bolt soon. Hopefully I'll have a free weekend sometime this month to throw it all in. Guess I should find an updated lower intake manifold while I'm at it.

I haven't been babying it, but haven't been flooring it either. Just my normal driving style. I've never been wowed by the results of seafoam and the likes, but maybe ill give that a shot?
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: jaccox on October 15, 2018, 07:37:42 AM
Should be easily seeing 15-16mpg with the 31's. Sounds like you're due for a ton of services (as to be expected after purchasing one of these gen2's) I'd definitely start with an oil change with a quality oil and proper weight. Not gonna suggest an oil as that's a good way to start a forum war lol. But will let you do your own research on that field. While on the topic of oil it's time to drain and fill the diffs, t-case, trans (with correct spec fluid, and you can drop the pan and clean the screen as well). That right there can cause some serious drag if any of those things are sludged up. Another quick and easy thing to do is jack the truck up at each corner and give each wheel a good whirl, listen for noisy wheel bearings or sticking brakes (guide pins on these trucks get stuck often). Now that we got the Rookie stuff out of the way lets start prodding around under the hood. Replace air filter and plugs and wires while your doing the timing belt especially if you have no record of the plugs or wires. Get yourself a good OBDII dongle and buy the torque pro app. Learn how to read fuel trims long term and short term. This can help you chase down air and fuel gremlins that could be causing poor economy. It won't single out something, but can give a good idea of where to start looking. The shift problem you describe when the trans is cold seems like your trans cable on the throttle body is out of spec (pretty common and easy to adjust), but these trucks do hold the first shift when cold to help warm the fluid up quicker.
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: Crumb on October 15, 2018, 10:35:58 AM
Sounds like it's down on power, the 94-96SR likes to rev and is the most powerful Montero sold stateside. Even up steep grades it should have no issues maintaining 65mph or even faster. Even up long grades with my SOHC it holds 65mph no problem. I'm thinking you have a timing issue or a restriction of power somewhere.
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: toby088 on October 15, 2018, 11:30:47 AM
When you say timing issue - these things donít have adjustable timing like an old car right? Computer just takes a signal from cam and/or crank sensor and uses that info to time the spark? Is there some way to adjust the timing?
I guess for now  Iíll just take my time going through this thing with a fine tooth comb, do the fluid changes and other maintenance, and see where that gets me. Might have time to finish diff and t-case service today if i get off work early enough. Crossing my fingers!
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: jaccox on October 15, 2018, 02:02:34 PM
I believe Toast is hinting at a motor that is possibly out of time (from improper timing belt installation, failing tensioner or stretched belt). Best bet with these trucks are to get the Timing belts, water pumps, timing tensioner OEM, and hoses and o-rings knocked out before they brick your engine. Plus you'll then set yourself up a maintenance schedule instead of guessing when something needs to be changed. The DOHC is the most difficult of the 6g74's to line everything up since you have two extra cams to get in time.
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: jaccox on October 15, 2018, 02:06:59 PM
Also would be wise to check the bushings on the butterfly shafts on the intake plenum. Those can cause a lot of headache and harm if they are failing. Can cause vacuum leaks or worst case the engine ingest the valve and then internal damage. If you do get down to doing the plugs and wires you could possibly rent a compression tester or even a leak down gauge and check make sure everything is good internally.
Title: Re: 10 mpg in a 1996 Montero SR?
Post by: Crumb on October 19, 2018, 07:42:13 AM
jaccox FTW! Good post, Thanks dude.