Weird "Roar'' ....High RPM???

[mikestoke]

2004 F-350 lariat SDD DRW ... I am driving down the interstate today and all of a sudden we hear a loud roar and i noticed the RPM's hit 3000, We were locked on cruze at 75 MPH. at first I thought it was the air conditioner blower but it is not. It lasted about 20 sec. then about 15 miles later it did it again. We traveled about 100 miles and it did it 4 times. I tried shutting the cruze off and it did not change but if I gave it more pedal the RPM's kept climbing.Has anyone ever experienced this? Thanks Mike

[jmaskew]

Do you have aftermarket gauges? The roar was probably your fan kicking on due to overheating and the 3,000rpms, since you where in cruise control, might be due to defueling. When the truck defuels it will slow down and since the crusie was on it was trying to maintain 75mph so the rpms kicked up. Just a thought. I've experienced a similar situation.

[mikestoke]

No I do not have aftermarket guages, but that does make sence. Thanks for the reply.

Mike

[cartmanea]

How hot was it outside? Our fans are pretty loud.

[mikestoke]

It got to about 102 but that is nothing new for Missouri and i had never heard that before.

[jmaskew]

Originally Posted by mikestoke

It got to about 102 but that is nothing new for Missouri and i had never heard that before.

Are you losing coolant? Look at your degauss bottle for white spots (dried coolant). I had a similar experience which turned out to be head gaskets. I would suggest a set of gauges and a coolant bypass filter.

[rphlipper]

I agree with Carmanea, our fans are pretty loud. I am towing a 5th wheel regularly and do experience the sound frequently since May driving in warmer climates. No sign I am losing coolant. I hope it's not head gaskets!

[Benchwrench]

If you're getting 3K rpm @ 75 mph you mostlikely have the 4.30 gears and the noise is normal when the electronic fan engages. At first it'll make you sit up straight because of the roar, this is a good time to look at your temp gauges. Hopefully you have "real" ones.
they really are nice to have for these trucks

[jmaskew]

Originally Posted by Benchwrench

If you're getting 3K rpm @ 75 mph you mostlikely have the 4.30 gears and the noise is normal when the electronic fan engages. At first it'll make you sit up straight because of the roar, this is a good time to look at your temp gauges. Hopefully you have "real" ones.
they really are nice to have for these trucks

The engine is jumping to 3,000 rpm's and the truck will not go any faster. He is defueling. When he takes it off cruise control and puts his foot into it the engine revs up 3,000 + rpm's but doesn't go any faster it just keeps losing speed. If you have been in a defueling situation (it sucks) it makes perfect sense in what he is describing. Something is overheating. A set of gauges would be nice so you can see what is overheating.

[Benchwrench]

in this case, what conditions have to be met in order for the truck to defuel?

[bismic]

Defuels at

Coolant temp 227
Oil Temp 254

[jmaskew]

Originally Posted by Benchwrench

in this case, what conditions have to be met in order for the truck to defuel?

I suppose without gauges you can't really tell what's over heating. When my truck defueled none of the gauges (stock) moved, it just lost power and the fan was roaring. What the OP is describing sounds just like the same thing that happened to my truck. I'm sure it could be 1,000 other things but it really sounds like it's defueling.

[Benchwrench]

it almost sounds like a transmission issue however I know of others who had this same thing happen only to find out it had to do with the injection control module where the truck would 'race' and wouldn't deliver the goods.

[mikestoke]

Thanks all for your input, Took truck in for some warranty work and the mec. said just what you said. The fan cluch kicked in,But he said he would take a look at it.

Mike