Exhaust pipes over-heating

I have a 77 dodge 440 engine in a class C motor home. Had new mufflers
installed and 600 miles later the mufflers are showing heat and the clamps
holding the mufflers on are turning blue from heat. It appears to be worse on
the right side.

The tail pipe got so hot on the right side that it melted a hole in the plastic
tank about 15 feet from the engne. The plugs are dark brown with some white
down inside the electrode.

The engine has good power and is getting 8 to 10 mpg does not get hot
according to the temperature gage, the Radiatror top is 194 deg and the bottom
tank is 174 deg. The fuel milage has always been in this range but I never
noticed the pipes getting hot before.
Any help someone may have will be greatly appreciated as I am stumped. Thanks
in advance. Marvin

 

Just a couple suggestions:

Are the new mufflers cheaper? Perhaps the old ones were double-walled the
new ones aren't.

Are the new mufflers significantly different, perhaps a heat shield got
thrown out instead of
being put back where it was supposed to go.

Is there any openings for air to be introduced into the exhaust system and
perhaps causing
a secondary burn in the muffler? Maybe they broke a seal when putting the
new ones on?

Ted

 

Check the vacuum advance can on the distributor- if it fails (and they
do... all too often) then the engine won't be getting enough ignition
advance during light-load and cruise conditions, and the exhaust will be
staying a bit on the hot side. With the engine at fast-idle (1500-2000
RPM), disconnecting the vacuum line from the advance can should produce
a noticeable drop in RPM. If it doesn't, check the can by sucking on the
vacuum line and seeing if it holds vacuum. If air moves through it
freely, its time for a new advance canister (the diaphragm is torn). If
it holds vacuum, then make sure its connected to the correct port on the
carburetor and that the carb is supplying vacuum (the port may be clogged).

Also, check the basic timing. Its a good idea to first verify that the
timing mark on the harmonic balancer is right, and this can be done with
a piece of coathanger wire inserted into the #1 spark plug hole and
feeling for when the piston reaches TDC as a helper rotates the engine
with a breaker bar.

But be aware, any time you ask a 440 to work hard, its GOING to heat up
the tailpipes pretty good no matter what. The pipes should be routed
well clear of anything that is heat-sensitive. I wouldn't be worried at
all about the "bluing" of the clamps and mufflers (especially if they
weren't aluminized or stainless steel mufflers) so the only problem
might be the routing of the pipe near the tank that melted.

 

Thanks one and all for suggstions. Will check timing. The only problem i gave
with that is I don't know what it is supposed to be I have no reference for
this.
Right now I have the timing set (withiut vac, adv connected to engine, idle
advance is 27 deg adv., 36 degs at 2000 RM. I put this rebuilt motor in three
yrs ago and the rebuilder set it like this to avoid burning a piston. Will
check farther into the timing situation. BY the way i am in Calif. and the smog
restrictions re horrific.
Thanks again to all.

 

I forgot what year your M/H is, but for most years 440's typically like
around 12 degrees initial advance (at idle, vacuum advance
disconnected), and 36 degrees total mechanical (vacuum disconnected) for
a stock distributor.. It sounds like you're fine on mechanical (27
initial isn't too much of a problem depending on what advance springs
you have in there, the 36 total is the important number). I'd check for
the dead vacuum advance canister, because a 440 will purr along under
minimum load with about 50 (!) degrees total vacuum+mechanical. That
will cool the exhaust temps down and help with fuel efficiency, although
I doubt you could ever pull enough vacuum in a big boxy motorhome to get
the full vacuum advance. You still should get *some* help at cruise, though.