Intake Air Temp

[Edward Buker]

This posting is to share an observation that caught me a bit off guard. Normally my intake air temp runs quite stable at about 15 degrees above ambient at highway speeds. I have added a tablet that provides a nice color screen display of the engine functions and replaced my original Silver Leaf unit due to a display issue.

One added feature of this system is that all the main monitor functions like oil pressure, oil temp, transmission temp, voltage, etc. have a colored indicator circle within the display window for each parameter. They will display green, yellow, or red depending on preset operating values for my C12. A quick glance to see all green indicators and you know you are good to go. You can also add audible warnings I you like.

I glanced over at the display after traveling several miles recently and the intake air temp that should have been running about 80F, was up to 172 degrees F and the indicator had turned yellow. I kept one eye on the gauge and eventually the temp wandered down to 80F, after maybe 7 miles or so. I had never noticed anything like that wild temp swing before so I was concerned.

I shared this observation with Gerald and he was kind enough to also check his coach for me on a recent drive. He also found a similar swing in intake air temp. After some monitoring and reasoning we both concluded that our cooling fans literally pull no air during warm up until the engine coolant temp gets to somewhere between 185F and 194F (depends on your particular wax valve). The turbo is rapidly heating up due to exhaust temp rising with boost and that is raising the intake air temp dramatically until the coolant is warm enough to turn the fan on and start to chill the air to air intercooler. Once the fan kicks on the system then maintains very good control of both the intake air temp and the coolant temp so the fan must stay on constantly. If not the air to air intercooler would heat very rapidly and I see none of that.

In that interval before the fan comes on you may see your intake air temp reach 175+ degrees. I've had this coach for a few years now and would not have noticed this characteristic without the new color monitor system. This post is to make other owners aware, and to not be startled if they happen to notice this intake air temp beings so high, apparently this is normal. Hope this helps.

Later Ed

[Rod Ogle]

Ed

  You have touched on a subject that has been driving me nuts for several weeks now.  I had to replace a broken fan mounting bracket and radiator shroud on our 04 C-12 Patriot recently.  After making the repairs I started the engine and quickly went to check if there were any clearance problems with the reinstalled bracket and fan motor.  I was expecting to see the radiator fan to be turning at cold idle…. but I saw no movement at all.

  Monaco tech support tells me that the fan motor should idle (slow speed) until the engine reaches approximately190 degrees  at which time the thermal valve (AKA wax valve) causes the fan to run at high speed.  The speed up from zero RPM to almost 3000 RPM is supposed to happen over a 12 degree temperature range, thus keeping the fan from going from stop to full speed all at once.

  I tested our fan motor and hydraulic pump and found them to be fully operational, leaving the thermal valve as the remaining suspect.  I replaced the thermal valve and still no fan movement at cold startup.  That was an expensive misdiagnosis!!

  Seeking more information, I called Source Engineering in Eugene and spoke to Scott, one of their engineers.  I explained my situation, and he asked if our coach was overheating….I said no…he asked if we had any dash warning lights….I said no… Scott then told me I had no problem and the thermal valve and fan were doing their job.  Scott said that some coaches had a restrictor valve placed in line between the thermal valve and the fan motor, thus forcing the fan to turn even at cold startup.  However, many coaches did not have this restrictor and the fan only turned after reaching thermostat temperatures…which seems to be your case also.

  I will keep a close eye on all engine, transmission and air intake temperatures to make sure nothing gets out of range.  But for now, no fan movement at cold startup seems to be the nature of the beast, at least mine and at least for now.

[Edward Buker]

Rod,

I do not know if my fan turns to some extent during the warm up part of driving. I do know that it is not being driven by hydraulics to the point that it is performing any effective cooling. That is clear because my intake air temp continues to rise until my coolant hits 194F which is very repeatable, the coolant temp will then drop to something like 188F and hold. The intake air temp at 174F dropped to 80F and stayed within a small range also. After that initial fan turn on the intake air temp and coolant temp stay in control which says to me that air flow is maintained at a high level constantly.

If there is a slow turn on of the fan somewhere in the 180s, and there may be, but I cannot see that with any coolant temp or intake air temp response, the response that I can see starts when my coolant hits the 194F turn on.

I will take a peek when I start up tomorrow and see if I get some RPM on the fan or if it is still. Whether it is spinning a little or still, to me it makes no difference in that it is ineffective (not being driven to effectively cool) until the 194F is reached on my coach.

I think what remains important from all of this is that once the fan turns on, that from then on you get full and complete cooling and temperature control of the engine coolant and intake air temp being maintained within reasonable bounds. Below the turn on temp, whatever your turn on temp turns out to be, there may be variations between coaches as to how much fan rotation you actually get. The point is it is not effectively cooling, so whether you have slow or no rotation, the end result is pretty much the same. That fan has to be turned on to effectively cool.

Later Ed

[Rod Ogle]

Ed

  Thank you for the explanation of your fan and subsequent cooling operations.  It makes perfect sense to me that it doesn’t matter if your fan turns when the engine is cold or not.  What does matter, that the fan does kick in when coolant temp reaches or nears normal operating temperatures,  then maintain temps within normal limits.   I thought we had an potential issue based on the reply I got from Monaco Tech support, see below. 

mcctech [mcctech@monacorv.com]

Normally with the engine cold, the fan should be just barely turning.  As the engine heats up, the fan should turn faster and max out at about 210 Degrees.  Your operating temps sound about right.

From: Rod Ogle [mailto:rodo3162@comcast.net]
Sent: Tuesday, June 02, 2015 1:51 PM
To: mcctech
Subject: Radiator Cooling Fan motor

Frank

We have a 2004 Beaver Patriot Thunder 505hp CAT C12, VIN: 1RFC6551743024805
While doing engine maintenance I noticed the hydraulic radiator fan motor does not turn at all when the engine is cool to warm.  I let the engine idle to achieve water temp of 120 and still no fan motor movement.  At what engine temp should the radiator fan motor come on?  Engine temps have been running 185-195 degrees while driving with an occasional bump to 203 going up hills.

  I am concerned the Charge Air Cooler, transmission cooler and hydraulic oil cooler may not be getting enough cooling.

Thanks in advance
Rod Ogle
Salem, OR

BTW, when searching for a vendor for a new thermal valve (AKA wax valve), I discovered they come with many different temp settings, I found them ranging from 160 up to 210 degrees.  The part number for the old unit in our 04 Beaver was for 190 degrees.

[Edward Buker]

Rod,

I did do a fan check this morning. I started up and let the coach air up and run for a few minutes before I went out to look at the fan. There was absolutely no fan rotation at all. After driving for a hundred miles or so, I took a break and rolled into a rest area. My coolant temp had dropped while sitting to 180F. I got out of the coach and checked while the engine idled, and by observation the fan was spinning very fast. So my fan turn on seems to happen at 188F to 194F. Once on it does not seem to turn off at least down to 180F....not sure where the turn off temp is. The high speed spinning of the fan (all the blades were just a white blur) confirms Gerald's point that the hydraulic pump even at idle has plenty of output.

For future reference I had my wife take a photo of the engine display while traveling at 63MPH, engine fully warmed up, fairly level road, at an ambient 75 degrees. The pink column near the center of the screen has all of the reference values for this coach. I would guess these are pretty typical values for a C12 without any issues.

Later Ed

[Joel Weiss]

Ed:

I haven't done a visual observation of my fan but my Silverleaf clearly displays the coolant temperature change when it comes on.  At ~194 the coolant temp rapidly drops to ~186-188 which I've always assumed was the fan turning on.  However, in my case, after the fast drop the temp will rise back up to ~194 when the process repeats.  I've always assumed this was due to the fan cycling on and off since constant operation of the fan seems as if it could take the coolant below 180F which is the lower recommended operational limit for the engine.  I guess it could also be the fan cycling from low speed to high.

With my new steel radiator expansion tank and a new 13psi cap, at highway speeds and ambient temperatures of ~<70F my engine appears to be able to "float" in the 190-192F range without the fan coming on (or going to high, whichever the case may be) at all.   Under those conditions the coolant temperature will slowly vary within that range with the fan only coming on occasionally to drop the temp back down if it creeps up to the 194 level.  Since I believe the thermostat installed by a CAT dealer a couple of years ago was a 195 one, this all seems consistent with how I would assume the operational behavior would be.  All I know is that the C-12 was quite happy cranking out its rated ~1550 lb-ft of torque with boost pressures of 22-26 psi as necessary.

We're currently parked for a couple of months on PEI but once we start moving again I'll take a closer look at the fan's operational behavior.

[Mike Groves]

Ed,

I'm just impressed with the fuel economy if those figures are what you get normally.  Maybe I should start going faster then I've been going. 

Nobody has said anything about the engine thermostat.  I thought that was the chief controller.  Mine warms up to 188 and might drive up to 194 but rarely higher, and typically comes back down again.  I have no idea what the fan is doing. 

Joel, I have my 3 selections as Engine Temp, Trans Temp, and Engine speed. 

What do you monitor?

Mike

[Edward Buker]

Joel,

If you have been following all of this post about the intake air temp and engine temp it is very clear that the intake air temp is very responsive to the air flow. During the warm up period of driving before the fan kicks on I have had my IAT rise into the 170s and drop into the 80s when the fan comes on. I also get the initial fan turn on with the coolant in the 194 region but then it drops into the mid to high 180s and usually stays stable there. I do not think your fan is changing speed much while running at highway speed, more likely the engine thermostats are varying the flow as the spring and diaphragm expand and contract related to the coolant temperature. You can check this by watching the air intake temp, if that is going up and down in sync with your coolant temps then it would be air flow driven by fan speed, if that stays relatively constant then the air flow is stable and the engine thermostats are regulating the temp variation. Either way as long as the temperature control system is adequate and stable on your coach then all is well. Knowing how it is all working now may help you or myself in the future if something changes. Each coach is a bit different which will vary results some.

Mike,

My coach is a California 40, a little shorter and maybe slightly lighter then some. I was down to about a quarter of a tank on the gauge if you saw my miles remaining display which made me lighter, carrying 1/3 tank of water, holding tanks empty. I seem to get better mileage then some, I typically average between 8 and 9 miles per gallon at fill up depending on conditions, long term about 8.5MPG. I travel mostly interstate at 61 to 63MPH by GPS. I consider myself lucky with that mileage.

Later Ed

[Mike Groves]

Ed,

Ok, I feel a bit better.  I am in that range as well.  I rarely go below a half tank - probably because I'd like to keep the purchase amount lower and I am typically carrying at least 30% water.

Thanks for clearing that up.

I'll see if I have air inlet temp accessible.  I think I do, so I'll watch that a little and see what I notice.

Thanks,
Mike

[Adam Hicklin]

Probably a dumb question but when you say "intake air" temp, that's different than "intake manifold temp" correct?

[Gerald Farris]

Adam,
No, they mean the same thing. That is just 2 different terms for the same thing because the intake manifold temp reading is for the air inside the manifold, and not the manifold itself.

Gerald