Intake Manifold Temperature

I'm running a VMSpc on a 2000 Monaco Dynasty. What, exactly, does the Intake Manifold Temperature tell me? What should I be watching for with that temperature indication? Is it an indication of the ambient air temp going into the engine?

Thanks,
Lew

One of my favorite gauges.

For most of us, the Manifold Temp is one of the most important gauges to watch. It measures the temperature after the turbocharger, and since the turbo is a major heat source (second only to the fuel combustion itself), it has a huge impact on your temperature management.

There isn't a "red line" value for this temperature, per se. Instead, you'll generally find that it will track the ambient air temperature, plus a certain amount that varies with the turbo design. When I'm cruising on a flat highway, my coach shows the manifold is almost exactly 40 degrees hotter than the outside air. So on a 80 degree day, it will read 120 degrees very consistently.

But that will rise rapidly when you start using a lot of turbo boost. I'll see a rise of up to about 30 degrees, and that heat all gets transfered to the engine. If I don't react (downshift, slow down) within a few minutes I'll see the Coolant Temp rise fairly proportionately. I use this to my advantage - if the manifold is only "a little hot", I'll just keep going as I was and ride out the hill.

For most of us, the manifold cools down much more slowly than the engine. This shows how much heat is still latent in the engine compartment, even when the Coolant Temp has been reduced to normal. In rolling or varied terrain you can often see a real heat buildup in the manifold. That build-up can lead to a nasty surprise - the Coolant Temp can spike up very quickly on a hill that doesn't seem so steep.

Finally, never shut down your engine when the manifold is hot. Once you know the "cruising" temperature differential - in my coach it's 40 degrees - you can check your manifold before shutting down. If it's already within that normal range, go ahead and turn off your engine. If it's hotter, idle the engine for a few minutes to cool off the turbocharger.

Why this gauge isn't in every dash cluster I don't know. I can't imagine taking a hill on a hot day without it.