twhite

I deliver RV trailers partime. While driving on the interstate under a load (towing a trailer) sometimes the temperature of the motor and transmission (I have a tranny temp gauge) will rise to a point where a loud noise occurs in the engine compartment. The temperatures go down somewhat and this loud noise stops. A tech at the dealership said that this is a fan that kicks in to assist the air conditioner when truck temperature rises.

However, driving under a load in "stop and go" traffic such as congested traffic on secondary roads or slow downs due to construction on interstates, the temperatures rise on the truck and tranny but this noise (fan ?) does not start. On a hot summer day, under this type of driving, the temps just continue to rise.

Why doesn't this fan kick on during the stop and go traffic? Is it designed NOT to kick on at this time for some reason? What can I do to keep the temps down during this stop and go driving? I am thinking of having an electric fan installed that I can turn on and off with a toggle switch for these types of situations.

All suggestions or comments are welcome.

Tim

Smokee

Sounds like fan clutch is intermittent. Withthe engine OFF, try spinning the fan. It should offer some resistance, but you should be able to turn it.

twhite

"Sounds like fan clutch is intermittent"

No, I dont think so. It does the same thing every time. It will come on while interstate driving when the temperature rises but will NEVER come on in stop and go traffic if the temperature rises.

I checked the fan. I can turn it easily. It offers almost no resistance.

Shovelhead

I've seen a couple of posters stating that they found alot of crud trapped in the radiator fins between the intercooler and the radiator.
Might give that a shot, if that doesn't help, maybe an electric Aux fan for the rad and/or tranny cooler could be of some benefit.

Smokee

Hmmmm. Sounds odd. For Interstates, the fan should not come on above a certain speed since it would be a restriction. The fan should engage in stop and go or idling. I think there should be noticable resistance.

twhite

Hmmmm. Sounds odd. For Interstates, the fan should not come on above a certain speed since it would be a restriction. The fan should engage in stop and go or idling. I think there should be noticable resistance

I guess I should have mentioned that the fan comes on only when I am driving in 3rd gear. When I tow in overdrive, which is very seldom, the fan does not come on. It seems to run at a lower temp when towing in OD.

Pa outlaw

that whole theory of spinning a fan for resistance i dont think that works well on these trucks,my fan had resistance and it was still bad,clutch can be good but the heat sensor could be badwhicj=h would make it feel good but is not kicking in,no dis intended but im going thru this with my truck,the way to know if your fan is goood is to listen for it,if you do not hear it it is not working, my fan on my truck sounds like a tractor trailer fan now that i put a new on on,it works and you hear it,when it comes in you will feel a drop on the engine power,ussually comes in around 200-205 off around 180s,just some helpful advice,all the post above are good post but ive replaced alot of these fans in my shop,listen for the fanand thats what i would look for first

infidel

twhite, I think your fan is performing normally, you just can't hear it engage as well at lower rpms.
If you aren't overheating don't worry about it.

Rhino

I agree.

I might add that unless you are in 3rd or OD and the torque convertor is locked up, you are shedding heat from the tranny into the coolant.

twhite

twhite, I think your fan is performing normally, you just can't hear it engage as well at lower rpms.

actually, I can hear it. It sounds REALLY loud when I am towing in 3rd. Sometimes I think I can hear it kick in when I am in OD but I cant be sure. But I know that it is NOT kicking in when I am in stop and go traffic. I can see the truck temp gauge and my tranny gauge climb up in temp readings.

Once in Atlanta rush hour I watched the tranny go over 220 and was thinking about pulling over. It was all stop and go traffic and the fan didnt kick in. Works fine though, when you are rolling down the highway.

Tim

fschiola

The fan clutch locks up when the temperature of the air going through the radiator reaches a certain temperature and causes the bi metal spring to lock up the clutch. The bi metal spring is on or in the front of the fan clutch. When you're in stop and go traffic there might not be enough air moving through the radiator to cause the clutch to lock up.

twhite

The fan clutch locks up when the temperature of the air going through the radiator reaches a certain temperature and causes the bi metal spring to lock up the clutch. The bi metal spring is on or in the front of the fan clutch. When you're in stop and go traffic there might not be enough air moving through the radiator to cause the clutch to lock up

Good answer. Sounds logical.

Is there any work around to get this thing to work in stop and go traffic? Anything other that installing another fan that can be controlled by the driver?

Thanks

Tim

wannadiesel

When the engine is idling or you're putt putting along at 25 mph, the fan isn't spinning fast enough to make a lot of noise or move a lot of air. Air speed's got nothing to do with it the fan clutch engagement, it's temperature sensitive. Even if there is zero airflow through the radiator, the bimetallic coil is going to get hot and lock up the fan clutch. I think Shovelhead's post above talking about gunked up radiators is the key to your problem. From your description the fan clutch is acting normally.

twhite

The fan clutch locks up when the temperature of the air going through the radiator reaches a certain temperature and causes the bi metal spring to lock up the clutch. The bi metal spring is on or in the front of the fan clutch. When you're in stop and go traffic there might not be enough air moving through the radiator to cause the clutch to lock up

fschiola, you win the prize. You are exactly right.

I finally had a chance to visit the local Dodge dealership and talk to the service manager. He got out the "big book" and looked up the theory and operation of the fan clutch for my year and model.

The temperature of the air coming through the radiator turns the clutch fan on and off by use of the bi-metal switch on the front of the fan assembly. In stop and go traffic, there (apparently) is not enough air flow (volume of air) for the bi-metal switch to close.

He suggested getting an after market pusher fan or puller fan. Has anyone out there ever done this? What results did you have? Are there any other suggestions to getting air to this switch other than using a puller/pusher fan?

Thanks

Tim

RustyJC

I notice the original poster had an automatic transmission. We had problems with coolant temps on our 1996 Dodge 3500 V-10/47RE going high when towing our 13,500 lb 5th wheel in Houston stop-and-go traffic in 90-100 degF summer temperatures.

The problem was that the torque converter was generating so much heat under these conditions that transmission heat was overpowering the cooling system, which had very little airflow at these low speeds. If you trace the factory transmission cooling circuit, the hot fluid from the transmission goes first to the heat exchanger in the radiator tank (dumping heat to the coolant), then to the oil-to-air cooler, then back to the transmission.

I found a B&M SuperCooler with 1/2" NPT inlet and outlet ports and plumbed this in with Aeroquip fittings and hose upstream of the radiator cooler (i.e., the hot oil coming from the transmission went to the new B&M cooler, then the radiator cooler, then the factory oil-to-air cooler). This greatly reduced the heat load that was being dumped into the engine coolant. Although I didn't need it with the V-10 due to having added a 205 degF fan clutch, it would really help to put an electric fan on the new transmission cooler to get rid of even more heat under stop-and-go conditions before it gets dumped into the engine coolant. These mods dropped my maximum coolant temperature with the V-10 from 230-240 degF (260 degF redline) to 200-205 degF (200 degree thermostat).

Please note - if you read the instructions on transmission coolers, they will normally say to install the new cooler after the factory oil-to-air cooler. This will ensure the coolest possible transmission fluid, but won't really help the engine coolant that much. The installation I'm suggesting above is intended to provide help for engine coolant temperatures.

As others have said, the fan clutch must be working as well in stop-and-go conditions. I've never had any problem with properly functioning thermal fan clutches not engaging in stop-and-go conditions. Many times (as in my case above), that's where the engine fan is needed the most, so it had better work!

Rusty