Recently I connected my laptop to the info port using VMSpc and program. While on a trip in the Rockies , I was able to fine tune and control the temperatures while climbing major passes.The monitoring was really great to have. The only problem I experienced was on descents , when the exhaust brake would kick in , the manifold temp would shoot up rapidly (visible only on the Silverleaf monitor) . An engine prot light would then come on on the Dash panel. As my speed would lower and the Exhaust brake would kick out , the manifold temp would drop and the light would go out. The maximum temperature I saw for the manifold was 275 degrees , but that was just momentary. It would quickly drop to under 150 after the Ex brake kicked out. The other temperatures were fine and well within normal limits. What is the maximum permisable temperature for the manifold intake ? Could there be another reason the eng prot light came on that I am not aware of. It seemed totally related to the Manifold temp. Thanks for your input ! Mark

Submitted by Robert Hicks on Wed, 2014-05-07 21:18


I've been puzzled over the cause of this temp rise. I've asked Cummins about the issue in several locations and no one seems to be able to tell me the cause. It is rpm dependent and since the engine is essentially at idle, fuel supply should be minimal? Martin you seem to have a clue -- can you explain? Just passed 10th year with VMSpc and 132,000 miles and loving it.

The problem relates to the exhaust gases being backed into the intake manifold while the exhaust brake is active. When this occurs the heat is also backed into the intake system where the intake temperature sensor read the high temperature. This event is really worse during a long downhill grade with the exhaust brake active. It normal for this to occur. However the exact opposite will occur with an engine brake operation. The heat in the intake manifold will decrease, so the engine coolant temperature will decrease.