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Old 06-08-2005, 01:29 PM   #1 (permalink)
13tony
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RPM's at 70 MPH and 80 MPH

Hi all. I am fairly new to diesels as I bought my 05 LS CC/SB D/A back in December. For some reason, yesturday I was on thr highway and my engine sounded louder than usual. I looked at the rpms at 70mph and it was at 2000. At 80 mph, I was at 2500. My DMAX is completely stock. Does this sound right. I have driven it plenty of times prior and towed my WW FS2300 with it on numerous occassions. I don't recall hearing the engine so loud. Maybe its cause I ahven't driven it in about a week. I must of just been used to it. Please advise if these rpms are normal. Kinda seems like it didn't go into overdrive.
BTW, at 40 I was at 1400/1500 rpms which sounds normal. Thanx
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Old 06-08-2005, 01:56 PM   #2 (permalink)
BigShrimpah
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you are proboably hearing the pilot injection shutting off because it can't keep up at higher RPMS, when it shuts off you get the typical diesel noise. Its normal.
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Old 06-09-2005, 08:02 PM   #3 (permalink)
VegasTinMan
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Sounds like the fan clutch to me.
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Old 06-09-2005, 09:06 PM   #4 (permalink)
WAskier
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Get some bigger tires on there and it'll slow the motor down at 80mph
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Old 06-10-2005, 11:02 AM   #5 (permalink)
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Your RPM's sound about right to me. I'm going with VegasTinMan on the fan clutch. That thing will start to roar and eat up some of your HP especially this time of year. Mine usually only stays on for a few minutes but you can definitely hear it.
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Old 06-10-2005, 11:22 AM   #6 (permalink)
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At 70 Mph I am at 2200 rpm. I am at 2000 rpm at 65 mph.

If you are stock the only difference between our trucks is that mine has no cat or muffler and 4" exhaust.

You didn't describe the sound so its hard to tell. If you are hearing a roaring sound that is that fan. If you are hearing more of a clattering sound that is the engine.

Your pilot injection won't cut out until you get over 2500 rpm. When the pilot injection cuts out the engine will be noticeably louder and clatter more but that is normal.

If you got bad diesel or diesel with some gas mixed in that could make the engine louder. That happened to me a while ago. When the gas was delivered at the station they put premium in tank. The engine was a lot louder with a loud knock.

If you hear a roaring sound that is the fan. It should only come on briefly and then go off. If it stays on then you probably have a problem with the fan clutch. Usually, the only time I hear the fan come on is when I'm towing on a warm day.

Just some advice. If you are not already, you should be using a fuel additive like Stanadyne or Power Service.
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Old 06-10-2005, 12:26 PM   #7 (permalink)
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I too am new to diesel. When towing the horse trailer the other week I heard a load roar from either the tranny or engine. Sounded like the RPM's doubled. I looked at the Tach and it looked normal. The noise was certainly alarming and would last about a minute or so and then quit. I was going up a hill and it was warm out. So after reading these posts I would assume that it's that fan clutch, what is that?
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Old 06-10-2005, 09:04 PM   #8 (permalink)
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Under normal conditions the fan spins only a percentage of the engine speed. When the engine gets hot, a solenoid engages which makes the fan spin the same speed as the crank. Look at that fan, imagine the kind of wind noise it would make at 2000 rpm.
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