I've been working on my '93 Jimmy (W) on and off for the last couple months (well, in reality, I've been working on it since the day I bought it in June 2010, but only the last couple months are germane here). Until this summer it was my wife's daily driver. Now that she has a 2000 Blazer the '93 Jimmy is mostly a play toy and back up vehicle for when I'm fixing up my '98 Jimmy.

In July I replaced the water pump and fan clutch. Ever since then I've noticed a loss of power and fuel economy. I've also noticed a terrible roaring noise every time I accelerate. I checked the fuel system (https://blazerforum.com/forum/1st-ge...re-data-73595/) and didn't find anything wrong. I also checked the compression (everything +/- 10% of 120) and the timing (perfect, advance worked correctly).

I did a lot of searching on the Forum and I think I've found the answer: bad fan clutch. I replaced the fan clutch with a new Hayden severe-duty clutch from O'Reilly's. If I understand the function of the fan clutch properly it's supposed to engage only when air temperatures get high enough. Any other time the clutch is supposed to allow the fan to spin freely and independently of the shaft, especially at high speeds on the freeway when air flow is sufficient to cool the radiator.

What I'd like to know is whether or not I checked the fan clutch correctly today. With the Jimmy cold I checked the fan and it wouldn't turn at all. I started it up, drove it five miles to get the engine up to operating temperature, and tested the fan again after I shut the truck off. The fan wouldn't turn. I ran it another five miles, stopped, shut off the truck, and checked the fan again. It wouldn't move. I drove a couple miles back home and did the same thing. The fan still wouldn't move.

As a control I checked the fan in my '93 Sonoma. It had also sat overnight and was cold. The fan moved easily enough on the Sonoma to turn about one and a half times when I pushed it.

Is my diagnosis correct or did I need to run the Jimmy longer before checking the fan? I'm going to Eastern Washington on Saturday and I'd like to run the Jimmy over there and have enough power to get over the pass.

 

The fan should spin freely especially when it's cold, if it is locked up then it's suck on 24/7 and killing your power and mpg's. So yes it's bad.

 

That's what I thought.

I removed the fan clutch tonight and it was completely locked up. I took it back to O'Reilly's and got a replacement under warranty. I put the new fan clutch on and it runs and drives beautifully. Now I'll be able to tackle Snoqualmie Pass with no problems.