Heater hose (2.5L)- Can I bypass the intake manifold?

It's on an '86, and I don't know much about these engine. The heater hose goes into the manifold, and out the back. I'd like to bypass it with new hose.

I'm not real familiar with that particular engine, but usually when a heater hose goes into the manifold, it is to ensure that the manifold maintains the ideal temperature for fuel atomization (minimal condensation and evaporation). Some engines used an exhaust crossover to do the same thing. If you bypass this, your emissions and possibly your mileage, will be affected. Most likely not in a good way.

What is your thinking behind wanting to bypass the manifold? IOTW, what are you trying to fix?

Spudboy

Just wanted to bypass to make things more simple, i guess. I wasn't sure what purpose that it served. Plus, I'd have to buy a molded hose.
It seems that the earlier enginges (2.5 and 4.0) had these, and the 4.0s actually had passages into the head as well, from the intake manifold.

I may try it and see, since I have some bulk heater hose. Thanks

It's real important, don"t by-pass it!

Is it because the engine is throttle body injected? I always thought cold air was better than hot, but maybe tbi needs hotter air. So is cold air only better for mpi?

Same on the carbed engine. As Spudboy pointed out, this has to do with fuel atomization, not heating incoming air per se. I believe the molded hose was about $12-14 at the dealer several years ago -- don't know if it has gone up in the meantime.

It sounds as if you really, really want to bypass this so I reckon you might as well try it out. I don't think the engine is going to explode.

Thanks for the input, maybe I won't bypass it. It's turning 36" Swampers, w/6.5 gears (custom axles- 9" center) I don't think I would be able to tell a diffence in fuel economy, because the speedo isn't working right now.

However I would like some info on what can be done to this engine to increase performance/longevity. It had 127K before the speedo quit.
It has a cracked exhaust manifold, so I'm looking into header options, and also looking for info on upgrading the intake. Perhaps a different TB and intake system.
If I'm not mistaken, the 2.5 engines kept the tbi for a while, but ditched the "heater line-through-the-intake manifold thing, as well as the tube that ran from the exhaust manifold heat shield to a flapper valve in the air filter box.
I've come across some info searching, and will continue to do so.
Thanks.

I think Hesco makes a turbo for the 2.5L.

Carbs and throttle bodies will ice up in cold temps. I used to have a 318 which had the crossover in the intake it plugged up the carb would freeze solid after about four miles on a winter morning. For about a week the engine would stall at the same intersection about 1/4 mile from work. I could see my destination, it was like perfect timing for about 5 days, one morning I investigated and the base of the carb was coated with ice. I understand piston engine planes could develop the same problems now that would be scary.

A "wet" manifold (one with fuel running through it, instead of just air) will want to be warmer to prevent fuel "puddling" and to encourage vapourisation. This is why MPFI manifolds don't have heat risers, and TBI/Carbed manifolds do.

If you are getting ripped on buying moulded hose, do what I did. Take the moulded part, duplicate it in copper line, and use 2-3" "vibration stubs" of rubber hose to attach the copper angle line. Et viola, you only have to spend a quarter, instead of $15, everytime you service the line.

If you click on the link in my sig, and go to "Works in Progress by Works in Progress," you'll see a pic of what I'm talking about - $100 of moulded heater hoses replaced with about $20 of copper line and $2 of rubber hose.

Failing that, PM me, send me the hose (the one you pull out,) and I'll see if I can't duplicate it for you.

5-90

Thanks.
5-90, that's a good idea (copper.) But wasn't there a time when they kept the tbi, and stopped routing the heater hose through the manifold? maybe 87-89?
What is the 'heat riser?'

Also, this motor needs a thorough maintenance job, as it was neglected and abused pretty bad by the prev owner. So far, I've done motor/tranny mounts, ps pump and hoses, new coolant (not a hard flush yet though.)
Next is ignition and 02 sensor, and a battery.
Do you have any links or write-ups on dealing with the 2.5, performance wise?
I don't want to dump a bunch of money into it, but it needs to be dependable and efficient.
It will be on 33s, 4.88, 5 speed, and will be the rig I take to trailheads and leave for a week or more. It's so ugly and beat, nobody would mess with it :wierd:

A "heat riser" is a connection between the exhaust and intake manifolds, meant to conduct heat (speaking in an automotive sense.) So, if you have the exhaust and intake bolted together, that's a "mechanical" heat riser. If you have them bolted together with a gasket, and passages through the intake for exhuast gas (without the two commingling,) that's a "true" heat riser. Both were fairly common.

I think you'll find the 2.46 to be a fairly solid motor - all my reports from the field agree on this point. I don't have a lot of writeups handy for the 2.46, but I'm sure a lot of the inline six stuff will apply with a little translation (hack off two cylinders, and remember that you won't make quite as much power...)

5-90

Look into a 91-94 2.5L MPI swap. These engines put out more hp then the TBI ones. Its fairly easy except you will need to swap dash harnessses bc the firwall conector is different. Good swap bc these engines can be found cheap from yj guys putting in 350's and 4.0L's..... By teh way I have an 84 with a 94 MPI in it. I have done a few things to up its performance but they cannot be duplicated with ease on your tbi system.

thanks Ghost,
what things in particular have you done to yours to up the performance?
How much did they cost and were they worth it? (over stock)

I've never dealt with engine swaps/wiring harnesses, but would like to do so. Would I have to be digging in the dash to swap harnesses?

CameronB said:

thanks Ghost,
what things in particular have you done to yours to up the performance?
How much did they cost and were they worth it? (over stock)

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Right now I have added a 4.0L throttle bodie, Much bigger than the 2.5L one and bolts up to the Intake. A TBI spacer, and no cat exhaust that is much freeer flowing. SHe has 4.10 gears and can turn the tires over on rock if needed. (33x12.50's) I have a stage 3 came that will go in when I bore my old 2.5L block .60 over. Plans include for the feuture are a way to get more fuel in the engine, probalby adjustable fuel pressure regulator and map sensor or even and adjustable CPS. The years of 2.5L I list all can take these mods easily with work.

CameronB said:

I've never dealt with engine swaps/wiring harnesses, but would like to do so. Would I have to be digging in the dash to swap harnesses?

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I was a n00b when I took on this task a couple years ago. The dash is easy reallly. Everything just goes right where it was when you pull it out. If you find a donner xj with a 2.5L from that year it is even easyer you just need to swap the dash unit. An extra set of hands makes getting it in and out easyer. I got both the body harness and the engine harness from a guy on here for less then $200.00 The local yards watned $200 for the engine harness alone! I fould a guy that was putting a 305 in his 94 yj on ebay and wanted his old motor out of his garage and scored his whole drive train for $75.... All in all I probalby have about $750 in the swap with all the wireing and sensors and fuel pump and little things that I had to replace. A wrecked 2.5L xj could be bought for that easyly. Heinsight being 20/20 that is how I'd approach it. Feel free to ask any questions of me on I'm really easy to talk to and not one of these arrogant types that you run into in the jeep world that know it all!