New here and need your comments.I have learned a lot on this great site. I have a 1981 f100 stepside 300 i6. Just added a t18 4speed with 331 rearend.What should I expect going to a 3;08 gear. I also need to know,will a bad pvc valve cause oil burning and to what extreme.I am losing oil and have no smoke or oil leaks. I RUN 235/75/15 TIRES. Which speedo gear do I need for this setup. 308 gear or 331 gear thanks. PS. I just bought the truck.

 

[font size="1" color="#FF0000"]LAST EDITED ON 01-Feb-01 AT 01:29 AM (EST)[/font][p]I really want to ask what you want to do with this truck?

Do you want more power out of it? or more mileage?


1988 F-150, SWB, 5.0 EFI (formerly 4.9 EFI), M5OD 5 speed, 3.08 gears, Summit shorty truck headers, Custom built Flowmaster exhaust system. Force 4 LP6000 lightbar, Federal signal PA-300 100 watt siren, Icom IC-V100 50 watt mobile radio. ================================================== ===========
1965 F-100 (just purchased 1/18/01), SWB, 390, C-6 auto. Dual exhaust, Not much else to do to it.

Can see both below.

[link:www.geocities.com/hotrodford_88/|Hotrodford_88's Webpage]

 

Since you are looking at a higher (lower numerical) rear end, I would assume you probably are looking to run somewhat lower RPMs on the highway or, if the first gear is a granny, to tone it down a bit. Going from a 3.31 to a 3.08 is only about a 9 percent drop in RPM so that if currently you are turning 2200 at 70 mph, the 3.08 will put it at 2050 at 70 mph. Not much of a difference for all the cost/hassle of a change. Tell us what the T18's ratios are or, if you don't know, what is the highway RPM and is first gear a granny?

 

With a 3.08 rear and running 10.50 15's I used to be able to turn 2200 @ 60.

Trail Rider

 

if you want better highway speeds, and have the GREEN to do it, a company called gearvendors makes and overdrive for the T-18. the webaddress is http://www.gearvendors.com
the only draw back i seen was that its expensive.
lr

 

 

I pull a 15ft bass boat andhave the t18 granny gear.If going to a308 gear from 331 rear gear is only 9 percent difference I will keep my present setup.This truck will pull great.I just thought itmight bebetter on the milage if I wentto the 308 gear.

 

You might get better mileage, but I think you would lose some of your towing ability. (Like I said, I think)

My dad had an 82 F-150 with the 300 and a C6, and he never got any better than 13 out of it. And he had stock wheels, tires, ad everything on it. Perfect tune, and everything but it just never got good mileage. It also had 2.75 gears, so it should have gotten a whole lot better than it was getting. He also had a campershell on it, but it was flush with the level of the cab so there wasn't any wind drag from the camper.

He no longer has it, mainly due to the mileage thing, and the engine he had rebuild was leaking from the rear main. But he found another truck cheap. A 91 dodge (I know forbidden word) for $1500, and it only had 45,000 miles on it when he bought it two years ago.

1988 F-150, SWB, 5.0 EFI (formerly 4.9 EFI), M5OD 5 speed, 3.08 gears, Summit shorty truck headers, Custom built Flowmaster exhaust system. Force 4 LP6000 lightbar, Federal signal PA-300 100 watt siren, Icom IC-V100 50 watt mobile radio.
=======================================
1965 F-100 (just purchased 1/18/01), SWB, 390, C-6 auto. Dual exhaust, Not much else to do to it.

Can see both below.

[link:www.geocities.com/hotrodford_88/|Hotrodford_88's Webpage]

 

Try Marvel Mystery oil on your oil consumption. You can add it to the crankcase to help loosen stuck/carboned rings and sticking valves and to clean deposits and carbon. Added to the fuel tank it cleans cylinder deposits.

I have used it in several vehicles and engines and am satisfied. It stopped oil use between changes and top end "TAP" in my used Escort. When I pulled the oil pan to change the gasket I was suprised to find a spotless bottom end at 140,000 miles. Works great in Lawnmower engines, too. If I recall the Mystery history, it is about 10WT oil and was first used (added to the fuel) to help lube the carb and top end of WW1 byplane engines. Marvel was a carb manufacturer. If you give it a try post back what you think... Nothin to lose but oil...

 

My father already got rid of the truck. That was one of the main reasons he sold it. Plus, the gas mileage factor.



1988 F-150, SWB, 5.0 EFI (formerly 4.9 EFI), M5OD 5 speed, 3.08 gears, Summit shorty truck headers, Custom built Flowmaster exhaust system. Force 4 LP6000 lightbar, Federal signal PA-300 100 watt siren, Icom IC-V100 50 watt mobile radio.
=======================================
1965 F-100 (just purchased 1/18/01), SWB, 390, C-6 auto. Dual exhaust, Not much else to do to it.

Can see both below.

[link:www.geocities.com/hotrodford_88/|Hotrodford_88's Webpage]

 

Bige53: With a granny tranny your high gear is not an overdrive and thus you should be turning about 2700 RPM at 70 mph. I bet you could go with a 275 gear (which would bring the highway RPM down to about 2250 at 70 mph) and still tow your boat. It depends partly on the weight of the boat, but if you only tow short distances and not up steep grades you should be fine, possibly even with a 247 gear (which I had in my 84 F150--that baby would turn 1350 at about 60 in overdrive and with a headwind I had to downshift. The old '84 was geared so high I could take first up to about 45 mph). A 247 should put you at about 2000 rpm at 70 mph which is like my '95s overdrive (and 3rd gear in my '84). The torque peak on the 300 I6 is at 2000 rpm and any engine is most efficient (that is puts out the most power per fuel consumed) at the torque peak and wide open throttle (WOT). You will burn a lot of fuel at WOT, but you will burn it efficiently. That is the reasoning behind overdrives: move the cruising speed to a lower RPM that is closer to the torque peak to make the engine work harder, but more efficiently. My key consideration would be decent highway RPMs (around low 2000s and sufficiently low first gear for normal take offs). Hope this helps.

 

bige53,

I have an 89 F-150 300 with the T-18 and 3.08 rear. It also has 30.5 inch tires, not sure what it came with for stock tires. I pull a 22' ski boat and have only had slow acceleration problems with it, and poor milage, but I don't expect anything great. I turn around 2700-2800 at 70 mph. Any type of uphill grade with over 5000 lbs takes a lot to keep moving with the 3.08s. I have considered going with a 3.55 but I'm fearful of high RPM's and heat. I've already had the head cracked a week after I bought the truck, not my fault but now I'll always be scared.

I average around 12-13 mpg unloaded and when hauling around 9-10 if I take it easy on the Interstate. With the granny the only hard part about towing with the T-18 is the very wide ratio's between gears and not being able to downshift when you need some extra takeoff. I would love the ZF 5-speed OD found in many of the 250's. Anyone out there have much experience towing with one of these trannies? I think the T-18 may be due for a rebuild in another year and I might consider replacing it.

Joey