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Old 07-05-2009, 09:18 PM   #1
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Intake Manifold Temp - Should I be worried?

Today was a blistering hot drive up I-35 in Texas. Before we had even gotten to the interstate, however, I noticed that the intake manifold temperature had climbed into the 140s.

Since I've had VMSpc, I've monitored a number of engine measurements. In the past, the intake manifold temp often ran around 118 degrees F. In the summer it would hover around 132 degrees. What worried me today was that it was running a constant 144 degrees and every time I kicked on the exhaust brake, it would spike to 157 degrees. All the while, the engine coolant temp cycled as normal between 185 and 191, depending on whether the thermostat was open or closed.

One other thing that I noticed was the the temperature seemed vary the opposite of the turbo boost pressure. When the boost was 19, the intake manifold temp would drop a few degrees but would climb again as soon as the boost pressure dropped.

Before we left on this trip, I carefully cleaned the Charge Air Cooler (CAC) and radiator "sandwich" I didn't shine a flashlight through it but the water coming off of it was clear when I finished. I was careful to spray cleaner (Simple Green) around the permieter of the fan, the part that normally clogs up first.

So,should I be worried? If so, what should I be worried about? What other information that I haven't shared would be helpfu.

Thanks,

Charlie

P.S. The engine is a Cummins 5.9. with a Number 53 block.
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Old 07-05-2009, 11:09 PM   #2
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Have you monitored your fan operation during a cruise? If the fan isn't running when the engine's cool then the intake charge will rise due to lower airflow. Once you lay into the throttle and the heat goes up then the fan engages causing extra airflow across the CAC.
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Old 07-06-2009, 08:27 AM   #3
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In reviewing my VMSpc intake manifold temperature I run about 130 degrees max. My readings were running in the low 130's for a while but this is could be attributed to the sensor fouling. I bough a new sensor and cleaned my original one and both had the same resulting temperatures. My original sensor caused an intake manifold temperature code to be set intermittently and the cleaning corrected that. The procedure I found to clean the sensor is to remove it and clean it in paint thinner. I just agitated it around in the thinner. The sensor then acts like new. Other cleaners such as contact cleaner did not work. When you remove the sensor it will have lots of carbon and oil on it and Cummins says this is normal. The sensor is located on the passenger side of the engine near the rear of the engine for a Cummins 5.9.
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Old 07-06-2009, 11:00 AM   #4
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Jim, thanks as always for your information. I'm going to pull the intake sensor to see if mine is clogged up like yours was.

Sknight, on the rear radiator models, the fan is always on. That is one of the problems because it is always sucking HP. As I indicated, the engine coolant temperature was operating 100% normally.

I called Cummins. The tech there could not find a specific spec sheet for intake manifold temperature but told me that the ECM monitors it and will de-rate the engine if it gets too high. I had no error codes set and the check engine light did not come on. Frankly, I kinda expected that answer which is why I asked the question here first.

I probably won't get a chance to test the engine again for a month or so after I pull the manifold sensor.

I'm alway nervous when conditions that I'm used to change. That is why I wanted a monitoring package - so that I could understand what "normal" looks like and tell when something is going out of wack.

In addition to physically removing and cleaning the intake sensor, I'll try the flashlight test on the CAC. It should be super clean but.......

Charlie
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Old 07-07-2009, 09:15 AM   #5
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I work on several drag racing cars that we monitor and record intake manifold temps on. First let me say that this is the temperature of the intake charge or air coming out of the turbo charger and through the intercooler into the motor and has nothing to do with the temperature of the motor or the water temperature. Normally the more boost the more compression so the higher the temperature of the intake charge. Outside air temperatures does have an effect on this temperature because the air is preheated before it comes into the motor. Without an intercooler and high boost these temps my get as high as 250-300* F. Therefore it is important that the intercooler is kept clean and as said already increased air flow by the cooling fan speeding up also helps. What I don't understand what was said about the intake manifold temp dropping as the boost went up other than the motor RPM increased and so did the fan drawing air across the intercooler. It really does sound like a dirty or bad temp sensor,
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Old 07-07-2009, 09:23 AM   #6
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Depending on how the charge air cooler (aka intercooler) is sized, manifold temps of ~20 degF above ambient temperature may be about the best you can get under moderate boost. The cooler can only approach the temperature of the cooling medium, and it may well be sized for a 20 or 30 degF approach. So, as the ambient air (the cooling medium) gets hotter, the intake manifold temps will rise.

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Old 07-07-2009, 09:40 AM   #7
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Thanks, Rusty. Your information is consistent with why I thought that I had a problem. Assuming a 102 degree ambient temperature and a 30 degree differential, I would expect to see, as I have seen before, a 132-3 degree intake manifold temperature. When it started riding at 144 and spiking to 157, I felt like something might be wrong.

I won't get time to pull the intake sensor as Jim suggested until this weekend. I suspect he is correct - it will be dirty. That dirt could be influencing the readings. I just wanted to ask if there is something else that I should be looking at, too. While I'm at it, I'll carefully check all of the piping from the inlet to the intake manifold, through the CAC. A preliminary visual check showed nothing wrong. I'm assuming that I would see a drop in boost pressure if there were some sort of opening between the turbo and then manifold and I wasn't loosing boost. If I were sucking air out of the engine compartment because of a piping problem prior to the air filter, I could see where that might increase the intake temperature so I'll concentrate on that part.

I cannot say for sure that I was getting more RPMS with the boost increases that lowered the manifold temperature. Assuming a constant speed and a hill, I would expect the engine load to increase and boost pressure to increase with it but without without much of change in RPMs.

I'm going to try a flashlight exam of the CAC at dusk this evening. I don't think that there is a dirt problem but I want ot be sure.

Charlie
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