Cheers everyone,

I had these odd temperature fluctuations so checked it and found the radiator to be leaking.
Today I replaced it and also put in a new thermostat. Tightened all the tubes and filled it up with fresh coolant and distilled water (50/50 mix).
When starting the engine the first time it was giving a strange rattling like sound.
It seems to me like it was coming from around the drive belt area. But the belt, idler pulleys and tensioner are new.
I noticed, when the AC compressor is engaged, the tensioner is not moving. But when the AC compressor is disenganged, the tensioner starts shaking a little bit.
Turning the steering wheel from left to right does not do anything.
So is the water pump now failing, too?

Thanks for any help and ideas!

Oh, and any hints on how to bleed that thing? There are no bleed screws?! I just topped it up and let it idle until hot, but coolant did not drop?!

 

Does the rattle change when the a/c clutch engages?

The tensioner bouncing around a bit doesn't really concern me. That's what its designed to do. When the a/c is running, the belt is under high load, so, more tension, and less bouncing of the tensioner.

 

Jack up the front end or put it on ramps. Remove the rad cap and run the engine till hot. Squeeze the bottom rad hose to help the air come up but watch for the fan blade. You're done when the bubbles stop coming.

You say it was rattling. Did it continue after it warmed up? Did you overheat it before replacing the rad? Sometimes when you have the truck sitting a while, the lifters will rattle with a cold engine. Should go away after warmup though.

 

No, hasn't been overheating. Rattle comes back even when hot.
I think it is bled just fine, when driving home the temperature went up and stayed at around 200-204°F and hardly fluctuated.
Can it be that the water pump is doing that sound?
Strange thing is that the noise sometimes goes away and then comes back.
Any idea what I might check?
Thanks for your help!

 

Do you hear gurgling from your dash? Is your radiator fan tight with no wiggles on the water pump? Gurgling would be air trapped in the system. A wiggle on the fan would mean an issue with the fan clutch or a worn shaft seal on the pump itself.

If you hear gurgling from air, if you're careful, you can burp it with the radiator cap. I have some nasty, really steep hills near my house. I'll drive up them a few times to get the radiator above the rest of the system. There are two notches on your radiator cap. Take several rags or paper towels and press down on the cap. Now move it to the first notch. Keep pressure on the cap and then gently release it. It will make a rude sound like flatulence. That's because that's what it basically is. (Be sure to excuse yourself.) Personally, I use those radiator caps with the release lever. Those are easier and safer to burp.

 

It's possible. Check around the water pump for any leakage. Can you post up a video with the sound?

You can take off the serpentine belt and run the engine for a half minute (don't do this for long). If the sound disappears, it's something in the belt path, like water pump, tensioner, pulleys, etc. If the sound continues, then it's elsewhere on the engine.

 

I did some bleeding again today with the cap off, there weren't any bubbles, also revved the engine a bit to make the waterpump push more water through. Temperature is steady now, so I assume there is no more air in the system.
Also the noise is now gone or at least a lot less, couldn't really hear it today. Very strange.
It is coming from the belt, that's very obvious to hear. Maybe will remove the belt and test again though.

But so far I'd say it's gone.

Another question: I removed thermostat and radiator, thought that would like flush out 80/90% of the coolant. Coolant capacity is 4.7 gallons / 17.7 liters according to the manual. I only was able to refill a bit more than 2 gallons?!
So should I do a complete flush now maybe? How do you flush it completely?