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Sasquatch 06-15-2009 04:01 AM

Heat riser tube
ok, when I got the 258 the previous owner had removed the tube and plugged the holes in the exhaust and intake manifolds. Well the plug he used came out of the exhaust manifold and now I need to either re plug it or replace the tube.
So is there a need for the tube being there besides warming the engine? The engine runs like a champ without it!
Your thoughts and anyone know the correct thread for the exhaust manifold side of the tube?


Jim_Lou 06-15-2009 05:54 AM

I'm not sure exactly what you're referring to. There's the tube that leads from the exhaust manifold to the automatic choke, the EGR system which passes exhaust gas into the intake manifold, the system that heats the intake manifold by passing exhaust gas under it, and the system that heats intake air by pulling it around the exhaust manifold and into the air cleaner intake snout.

I think the EGR system comes closest to your description. The engine will run just fine without it, but the carburetion might need to be adjusted for best performance. The other systems I mentioned have to do with engine warm-up, so without them it will be a little cold-natured but otherwise run fine.

In a stock engine there are no threaded holes in the EGR system, IIRC, so the P.O. must have tapped the passage, probably with a 1/4" pipe tap, but anything is possible. Just try several things about the right size until you find what fits.

Sasquatch 06-15-2009 09:40 PM

1 Attachment(s)
Here is a pic of a couple of the tubes that I'm speaking of.
I plan on just plugging it back up as you can see in that pic the end in the exhaust manifold is destroyed when removed and in one of those tubes the buildup is actually blocking the tube anyway.

Jim_Lou 06-16-2009 05:32 AM

Those look like they would be part of the EGR system, but I don't know for sure - they're from a much newer Jeep than mine.

Pete88YJ 06-16-2009 03:19 PM

Yup -that's an EGR tube for a late 258. You can plug both ends, but your EGR won't work, if that's important to you or your state emissions station.

I'm not sure what the thread is.

Good luck

Jim_Lou 06-16-2009 04:27 PM

It would almost have to be a flare fitting. Send a picture looking in the open end for confirmation. Doesn't matter, though; you won't find a plug for it.

Sasquatch 06-17-2009 10:06 PM

It is a flared fitting.

Jim_Lou 06-18-2009 05:51 AM

Yep. I don't think there's a commercially made plug for it, and IIRC the thread size and pitch don't match any common bolt, although I could be wrong there. Best bet is to cut the tube next to the nuts and braze or weld it tube closed.

Saddle Tramp 06-18-2009 11:41 PM


Originally Posted by Pete88YJ (Post 1546345)
Yup -that's an EGR tube for a late 258. You can plug both ends, but your EGR won't work, if that's important to you or your state emissions station.

I'm not sure what the thread is.

Good luck

No emissions to deal with in the middle of Washington State but the advantage to having an EGR valve is it keeps the combustion temperature in the cylinders down which help with the longevity of your engine. I don't think it cost you that much to have it functioning.

Sasquatch 06-20-2009 04:57 AM

None of the rest of the egr stuff is connected, I wouldn't even know what to connect as it's a 89 YJ that had a mess of emission stuff that is all gone now.
I would have no problem replacing the tube but as I said both the ones I have are ruined from trying to unthread the exhaust manifold side. In the pic you can see the straight tube one is mangled but the flex tube one is also shot as the fitting is ovaled from wrenching. :/
Maybe I'll try Napa and see if they have the part but as I said the P.O. had a plug in it and as suggested in previous replies a plug wouldn't exist for a flare fitting so not sure if the threads are shot as well. :/
What I do know is that the dang engine runs like a champ and I don't want to harm it or do anything that would make it run any less ballsy than it is.
As for your heat comment, How is recycling heated air into the system going to make the temp in the combustion chamber lower? Seriously? I'm no scientist, only thing I can think is it's going to dilute the air making it less combustible and in hand less efficient.
Am I totally missing something here?
I have had many engines and this is the first that I can remember where I have seen a direct hard tube that size going to the intake manifold from the exhaust malifold.

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