Manifold heater

[CraigSmith]

I have so many questions I've been afraid to post, but here goes.



I don't understand the manifold heaters. The manual says if the wait to start light is on do idle for about 3 minutes to all the heat cycle to complete. (It would be nice if they just had a light so you would know if it was done. ) The dealer told me not to the this, so I stopped, but I think the engineers know more than the dealer. Heated air is certainly good for the engine. So what I've been trying to do is drive slowly (under 19 mph) until the cycle is complete. Then I get the best of both worlds.



However, it is extremely difficult to find a place to drive that slow without blocking traffic. Why do they shut it off at 19? I assume because the airflow would be too great above that to do any good? It would be nice if we could at least drive 25.



Of course, the manifold heaters come on any time the air is cold even if the wait to start light doesn't come on, yet the manual doesn't mention anything about waiting 3 minutes then.



Why doesn't it come back on any time you drop below 19 and it's cold? When I'm at a long light I'll shut down, and then when I turn it back on the heaters start up again. It doesn't make sense.



So what do you recommend, idling or driving? I can get a head start on the idle time by using remote start, but of course without the exhaust brake on it's wasting some heat.



It seems they could have been a little smarter about all of this.

 

[Hoefler]

When the wait to start light goes out, start it. It will continue to cycle them off and on until the engine reaches a certain temperature.

 

[CraigSmith]

Actually the cycle will turn off as soon as you exceed 19 mph. This is in the manual and can also be observed in practice, at least with my truck.

 

[HBarlow]

All diesel engines require some type of heaters to permit combustion when cylinders are very cold. Our Cummins engines use a grid heater which is high current wires stretched across the air intake. The grid heaters draw very high current, something like 90 or 100 amps iirc.

Proper operation is to always wait until the light is extinguished before starting unless the engine is already up to operating temperature. Let it idle until the heater grids stop cycling. You can tell when the grid heaters are cycling because of the reoccurring very large drop on the voltage gauge on the dash. Allowing the ECM to stop cycling the grid heaters before driving also allows adequate time for engine oil and tranmission oil to warm up a bit.

 

[AClayton]

I agree... . let the engine go through some heat cycles with the heater grid and allow vehicle to warm up for a few. I was always told to just drive slowly and carefully until enough engine heat is developed. I have no scientific evidence to confirm this, but real world experience tells me that speeds above 19mph ..... and driving with care... . will sufficiently and safely warm the engine without the grids. Fueling the engine even and low spds will perform better than the grids IMO... ... . again,providing you fuel the engine slowly and carefully until up to operating temp.



Alan

 

[CraigSmith]

Thanks. Initially somewhere I got the idea that not letting the grids complete their cycle will damage them, but I can't find that any more and I can't imagine how. I think they just must have been saying it's good for the engine.

Anyway, I'm not sure what damage I've done to the truck during it's first winter but hopefully nothing major; I wish I had gotten on here a long time ago.

 

[CSkal]

I usually start the truck and let it warm a bit while I put away my block heater cord, then drive away. When the engine is cold, I limit the RPMs to 1800 until the temp gauge gets close to normal op temps.