My 2001 Blazer cranks fine and makes no noise (ie quiet idle etc.) but when I accelerate it makes a roaring noise it usually starts about 30mph and gets really loud about 50 mph and stays roaring until I slow back down under 30 mph or just stop completely and then as soon as I start going 30 mph or more hear comes the noise all over again.
Can anyone tell me what might the cause? I was concerned it was stuck in 4wd but it shifts fine and goes into overdrive.

2nd question...... Strong vibration at hwy speed.

 

First thing I can think of is to check your engine fan clutch to be sure it is functioning correctly. With the engine OFF, see if you can easily turn the fan by hand. If not, you have a bad clutch. Let us know what that check shows you.
For the vibration, have you rotated and balanced the tires? Also, have you had the alignment and front suspension parts checked? It could also possibly be bad U-joints.
And, [sm=welcomesign.gif]to the Forum.

 

I'm putting money on the fan clutch as well. Probably is making your mileage suffer too!

There are causes for vibration. Tim Hanr (hanr3) posted a good thread somewhere about vibration diagnosis. I'll see if I can find it when I get a chance.

 

Ok..I went and spun the fan. It doesnt go flying around it makes about a half to 3/4 revolution. Wasnt bound or anything.

As for vibration..yes all that was done and new tires installed. Someone told methe ball joints may be bad.

Forgot to mention..116K miles

 

I think the fan should be freerer than than when you spin it. Might want to have it checked out.

 

Yes definitely more free than that. I had a bad fan clutch, I could only spin the fan 1/4 turn, and it was hard to spin. Got the clutch replaced, it free wheels quite nicely.

 

vibrations
https://blazerforum.com/m_25271/tm.htm

 

Yea im putting money on the clutch fan being bad!!

 

i have a similar problem but it did it while it was idling and when i accerlareated to like 10mph then it would stop, you think its the same proble?

 

No tippman its the clutch fan making the sound but it stops when you start going, so I think yours is a temp related issue maybe!!