91 GMT400 6.2L FFM heater leaking, need Help!

[GM Guy]

Hey guys,

we are running out of trucks to patch up for the trip tomorrow, and now I brought the 6.2L out of winter storage. we are changing filters (did engine oil last fall, only got 150-200 miles on a change) and we found a huge rats nest in the airfilter. Thanks to the Detroit gods for keeping it safe, the filter was uncomprimised, stuff was just around it.

got the fuel filter changed without much issue, but during bleeding, found my fuel leak. It was the fuel heater.

so we got the heater out (it is just push in, I assume the bleed screw actually holds it in, as it overlaps. and the o-ring is a little square. heater and o-ring look to original. (heater top says 3-91, so I am sure)

so do you guys think a o-ring will fix it, or it almost looked as if the fuel was coming up around the wires. do the fuel heaters fail like that and allow fuel to come up?

what can I do to get by if it is that? can one disassemble the heater and block it up with some siliconed up whittled wood? Or are o-rings common enough issue that it is probably just that.

any insight on the issue would be appreciated, thanks!

 

[bk95td]

I've heard of them leaking from both the oring and the wires. Try the o-ring and if it turns out to be the wires, cut them off and epoxy them over after a real good cleaning. It's warm enough out you don't really need the heater.
Penninsular diesel was selling brand new 6.5 style ffm's for $75. The new heater would cost most of that. The 6.5 style ffm should plug right in to your connectors.

 

[GM Guy]

ok, got all wound up over nothing! (what else is new)

turns out the o-ring did the trick. luckily old man has a 40x60 ft shop filled to the brim with junk, as it took us a while but we finally found the right o-ring to go on the presumably metric heater. will be changing it later with a GM one, that is sure to be viton.

got the ol girl lubed and filters changed, so we are ready to roll in the morning.

thanks for the suggestions barry. do you personally like the round filter better? other than having minor lower bail re-fastening issues, I almost like this style, as I am none too impressed with the new style cartridge that does away with the big plastic nut. I do like the old round better, it seemed more thought out.

I dont know, I am still on the fence on what to do with the truck. it is super nice and clean, but who would really want a 2wd 4spd 6.2L RCLB for a collectors item? I am on the verge of finding an NV4500, j code intake, deleting all EGR, and making this the Naturally aspirated fuel mizer ride.

 

[bk95td]

ok, got all wound up over nothing! (what else is new)

turns out the o-ring did the trick. luckily old man has a 40x60 ft shop filled to the brim with junk, as it took us a while but we finally found the right o-ring to go on the presumably metric heater. will be changing it later with a GM one, that is sure to be viton.

got the ol girl lubed and filters changed, so we are ready to roll in the morning.

thanks for the suggestions barry. do you personally like the round filter better? other than having minor lower bail re-fastening issues, I almost like this style, as I am none too impressed with the new style cartridge that does away with the big plastic nut. I do like the old round better, it seemed more thought out.

I dont know, I am still on the fence on what to do with the truck. it is super nice and clean, but who would really want a 2wd 4spd 6.2L RCLB for a collectors item? I am on the verge of finding an NV4500, j code intake, deleting all EGR, and making this the Naturally aspirated fuel mizer ride.

They both have drawbacks. They both leak after they get older. They both are messy when you bleed them. The round ones are still available new. I like that I can actually look at the filter in the round ones. I sold all but one of the square one to people with leak troubles. I even shipped a couple to Canada because the junkyards are stripped of them.Having all one style saves having to stock 2 different filters.
As far as anyone collecting 91 trucks, I doubt that will happen for at least another 20 years. It has to be more of a personal thing at this point. Keeping them in good working order is as bad as if you drive them all the time or worse. My 2 cars are a pia. I put new batteries in then every 2 years. I finally just went to buying junkyard batteries. I haven't driven the monte carlo in 4 years or more.
The 91 k2500ld 6.2 i used to have was very easy on fuel especially on interstate runs[80+mph]. I got as high as 28 mpg one time. That had a 4L60[700r4] and 3.70 gears,245-16 tires. A manual tranny should do better. I would think a lighter 5 speed from a gasser would hold up just fine behind a 6.2. Much cheaper than a NV4500.

 

[oldtoyboyd]

I have a 91 6.2/sm465/3.21 rclb that I am daily driving. I think I am going to turbo it. I can't decide between a 4l80 or a nv4500. It gets 20 mpg as set up now.

 

[bk95td]

I have a 91 6.2/sm465/3.21 rclb that I am daily driving. I think I am going to turbo it. I can't decide between a 4l80 or a nv4500. It gets 20 mpg as set up now.

The turbo will drop your mpg by 2-5mpg. Manual trans swap would be easiest.

 

[oldtoyboyd]

The turbo will have that much affect on mileage? If I don't go turbo, the 4l80 will suck too much power away to use it I think.

 

[iamdave0887]

If your looking for mileage a turbo isn't the best choice. Turbo means more fuel, more fuel does mean less MPG. However it's a double edged sword so to speak. an engine with more power won't have to work as hard(less go pedal input needed) so you may see slight gains in MPG. It really depends how you look at it, and what you are doing with the truck.

If you want the best mileage out of the engine then a nv4500 will suck less power than a 4L80E will. Not to mention you'd have to install sensors, a TCM, and a wiring harness for the 4L80E trans.

 

[tanman_2006]

I dont know, I am still on the fence on what to do with the truck. it is super nice and clean, but who would really want a 2wd 4spd 6.2L RCLB for a collectors item? I am on the verge of finding an NV4500, j code intake, deleting all EGR, and making this the Naturally aspirated fuel mizer ride.

Jerk is stealling my idea! :incazzato:

Haha, just messin with ya. I prefer an auto in anything I will be driving around town but if it is a farm truck NV4500 is the only way to go. I am looking more toward the 80's models JUST to have something alil different. There is a tempting 91 6.2 ECSB 700r4 2wd w/ 20's for sale close by that is looking more and more appealing. I would love to have and 80's 3/4ton yada yada, i have a thread over my search.... My problem is finding a classic 80's model 3/4ton with a good body that some one just DOESN'T want.

 

[WarWagon]

The turbo will have that much affect on mileage? If I don't go turbo, the 4l80 will suck too much power away to use it I think.

MPG drops with a turbo in general driving. After all you give the pump a 1/4 turn to use the turbo. Most of the time you are not using the turbo and it is just restricting the exaust. This is diffrent if you load the truck, have lots of hills, or tow. Then the turbo helps because you need the extra power. Using other than a GMx turbo can get you better results.

 

[tanman_2006]

I have a 91 6.2/sm465/3.21 rclb that I am daily driving. I think I am going to turbo it. I can't decide between a 4l80 or a nv4500. It gets 20 mpg as set up now.

If you dont tow you don't NEED a turbo or 4L80. A nv4500 would be a fairly simple swap but after that you would need to get lower gears. You would barely be spinning 1500rpm at the most if you kept the gears the same. This would cause a bogging effect and would decrease MPG. If you want an auto trans and wont betowing often and dont have a turbo I think a 700r4 would be ok

 

[Acesneights1]

Is the wiring interchangable from the old square FFM's to the newer round one ?