Trying to identify what these underbody pipes/conduits carry – Help!? (1 Viewer)

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Joined
Nov 27, 2019
Threads
1
Messages
9
Location
New Jersey
Hi Everyone,

I hope this is the right place for this question. I have a 1997 40th from the Northeast and it has some frame scale rust that I'm in the process of blasting and grinding off. Part of the rust is on the catalytic converters/exhaust manifold (which I am replacing with a magna flow cat pair), and while looking it over I noticed two, ~ 1" metal pipes routing from under the door frame across and above the cats and into the floor board under the passenger seat. They are very rusted and would need to be replaced, but what do they do?

Many Thanks!

Rusty Tubes.png


Rusty Tubes 2.png
 
Rear heater lines
You need to replace those or do a bypass with hose on those sooner than later.

To replace the hard steel lines, you must drop the transmission, so go with the hose bypass. Route them away from the top of the catalytic converters, but do it soon before they start to leak!
 
Thanks for the replies, folks! I've seen a few threads here that detail the operation. I'd rather not drop the tranny to fix the heat, but I do use the truck to drive into the VT/NH/ME region during ski season, so heat is a must.
 
dude bypass those today, they will not last up here in northeast and youll be bumming. hit up landcruiserphil or witsend tonight
 
You need to replace those or do a bypass with hose on those sooner than later.

To replace the hard steel lines, you must drop the transmission, so go with the hose bypass. Route them away from the top of the catalytic converters, but do it soon before they start to leak!

@BILT4ME does this apply to 91/92 (3FE motor, for the uninitiated) trucks, too?
 
Last edited:
Thanks for the replies, folks! I've seen a few threads here that detail the operation. I'd rather not drop the tranny to fix the heat, but I do use the truck to drive into the VT/NH/ME region during ski season, so heat is a must.

Rear heater not front heater. If you look under the front PS seat you'll see the heater core and fan. It can be completely separated from the rest of the cooling system, hence bypassed.
 
Understood! I meant that I need rear heat too, as I'll have my kid back there.

What would leak out of the heater core? Are the hoses/pipes carrying hot air or is they powering some heating unit under the seats?

Thanks!

Rear heater not front heater. If you look under the front PS seat you'll see the heater core and fan. It can be completely separated from the rest of the cooling system, hence bypassed.
 
Understood! I meant that I need rear heat too, as I'll have my kid back there.

What would leak out of the heater core? Are the hoses/pipes carrying hot air or is they powering some heating unit under the seats?

Thanks!

Engine coolant. That is why it's critical to replace ASAP
 
The pipes carry coolant to the heater core. The pipes will rust and crack and you'll be stuck on the side of the road wherever that happens. The rear heat is superfluous. Your kids won't freeze without it.

However, if you have a leaking rear main seal which requires dropping the tranny then by all means replace the hard pipes at the same time. There are 2 different sets, replace both.
 
That was the first gift my 80 gave me... The rusted rear heat tubes blowing out and puking all over the floor. At least it did it in the garage. I bypassed the rear heat and really have no complaints about getting the full cabin warm enough with just the front heat.
 
Just did a bunch of research from all the pointers and know what needs to be done. Will bypass first and consider replacing (and unbypassing) if needed. I don't think I've turned the rear heat on yet, actually... So I tested it and it still works, for now. Many thanks for all the advice!
 
If you haven't found and read through the FAQ give that a look. Hours of material in there.
 
Not 100% sure, but I am guessing it is. @jonheld can confirm.
Exactly the same on all US spec 80s.
Not sure if the part numbers match, but if you have a heater under the front passenger seat, the lines are there.
 
Yep. You could smelt ore in my truck, even on days when it's -35F.

No doubt the front heaters are impressive..... however the rear heat is great for keeping the kids in the back warm without having to get roasted out up front.

Random side note - I'm surprised someone hasn't ducted the rear heater air output externally and connected the fan to a thermostat so that it can be used as an additional radiator in high engine load/temp situations.
 

Users who are viewing this thread

Back
Top Bottom