we discovered today that we have a cracked exhaust manifold on our cummins 8.3 ISC. local diesel repair shop says this is pretty common in motor homes. anyone concur ? looks to be about $1000. in parts to replace. (estimate from Cummins northwest)we noticed a loss of boost pressure and a higher than normal EGTs the last hour of our return trip yesterday. Today Started the inspections to see why, and found the crack is totally around the casting between #2 and #3 cylinder. fortunately nothing burned in the area.

Yes, it's a very common failure mode. How many miles on it?

sch911 wrote:Yes, it's a very common failure mode. How many miles on it? a bit under 50kCause ?

Between 2 and 3 or 3 and 4 (in the "larger part") not the short front part??

wolfe10 wrote:Between 2 and 3 or 3 and 4 (in the "larger part") not the short front part??Read the post.

cracked exhaust manifold | Good Sam Community

29 Replies

ILVMYGT
Explorer
Oct 05, 2016
I installed a exhaust brake on my diesel pick many year ago. The brake activated when the engine went to idle. My experience is that the exhaust gas temperature (EGT) dropped to ambient.

Maybe it's when the exhaust brake activates. When going up a pass the engine is loaded and as soon reach the top and go down the side you activate exhaust brake. This could be cooling the manifold faster then normal.
Ivylog
Explorer III
Oct 02, 2016
DSDP Don wrote:
When you use the exhaust brake for extended periods of time on a downhill, the engine/exhaust temps go up.

I have a true Jake so no way to test this theory BUT the throttle is at the idle position... very little fuel so how is the engine/exhaust temps going up. :h My engine temps go down when using the Jake on long downhills.
doc_brown
Explorer
Oct 02, 2016
johnhicks wrote:
Assume $2500. The tech will break a bolt or two. It's common.

That's what it cost me to replace mine, and no bolts were broken.
DSDP_Don
Explorer
Oct 01, 2016
I have no evidence......but this was discussed before on another forum and there is a theory that excessive use of the exhaust brake is a leading cause of the 8.3 manifold failures. When you use the exhaust brake for extended periods of time on a downhill, the engine/exhaust temps go up. I know you can't just quit using it, bit possibly limit it when you can, especially when not needed, like around town.
Passin_Thru
Explorer
Oct 01, 2016
Rebuilding a turbo is easy. Good Torque wrench is a must.
Tom_Barb
Explorer
Oct 01, 2016
Ivylog wrote:
I found this video on ISL exhaust manifold replacement... DIY.

Using the WX 40W turbo part from the above I came up with a $158 turbo cartridge that may be all that's need to rebuild a ISL turbo. Need to do some more research once I get my exact turbo # to make sure the turbine wheels are the same. Because the link has a percent sign in it you will have to search Ebay for CUMMINS ISL Engine 6BT HX40W to find it.

That is the same Vid shown above.
Ivylog
Explorer III
Oct 01, 2016
I found this video on ISL exhaust manifold replacement... DIY.

Using the WX 40W turbo part from the above I came up with a $158 turbo cartridge that may be all that's need to rebuild a ISL turbo. Need to do some more research once I get my exact turbo # to make sure the turbine wheels are the same. Because the link has a percent sign in it you will have to search Ebay for CUMMINS ISL Engine 6BT HX40W to find it.
Tom_Barb
Explorer
Oct 01, 2016
The biggest clue that you have a cracked manifold on a cummins is a sudden rise in EGTs and a lower boost pressures.
Roger_in_VERMON
Explorer
Oct 01, 2016
Earlier this year for us 76,000 miles. Done by Cummins in Louras SC
Tom_Barb
Explorer
Sep 30, 2016
TANDDANDBIGE wrote:
Is this cracking issue a "IF" or a "WHEN"? How common is it? How often do the turbos fail? I hope my 8.3 330 is one that doesn't fail...... about to replace the aluminum radiator with seeping tube joints.$$$$; I will do that myself.

Motor trucks say they replace about 6-8 per year. in motor homes.