My truck sitting at idle will climb to the 210-215F range fairly quickly. The fan will then kick on, and it never actually gets to 220F. It will stay in that temp range until I get back to moving again. Once up to highways speeds the temp drops fairly quickly, it drops back down to normal operating range, and stays there at highway speed. Only idle or very low speed city crawling will cause the temps to climb again.

At nearly the same time as the overheat condition began, the AC quit working (its not blowing cold), and I believe the heater core maybe be toast, as my nose detects that sticky sweet stink inside the cab. Could these all be related, or just coincidence?

I pulled the passenger side dash apart, and verified the evaporator is ice cold and frosty. I guess the heater core is on the engine side of the firewall?
Any ideas as to whats causing the overheat? Sure hope its not an EGR thing sitting at idle?

I had this happen at one point and I cannot remember what the issue was.
I ended up having to pull the air line off of the clutch on the fan to make the fan run constantly, to keep from over heating every time I had to do slow maneuvers.
I will try and remember what it was, it happened a few years ago.
Wasted allot of fuel with the fan running constantly, but it kept the engine cool and the AC worked.
Might have been junk in the radiator or the water pump going out. Check the little seep hole at the bottom of the water pump and see if it is dripping.

Check out your fan clutch ... I may be kicking on, but how's the actual friction material of the clutch. I just put a new one on at 260k miles. Mine would randomly work well, then not work at all, depending upon where it hooked up when engaged.

Might try checking the coolant % (or temperature mark on the mix ratio) it could be diluted too much to give good cooling factor...but the EGR is probably the most likely issue.

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I guess I should have mentioned the clutch fan was replaced less than a couple thousand miles ago. The truck never actually overheats, it gets up there but then the fan kicks in and brings it back to the 210 area. It wont get any lower until I get air moving again. I did run water through the radiator to clean any gunk and bugs that may have built up.

If you are smelling antifreeze in the cab, you have a bad heater core. When they leak it may go in either direction, into the cab, try pulling up the carpet and mat on the passenger front floor, or to the front of the firewall, which will be harder to see and track.
Is it possible you have a thermostat that is stuck shut? I think the ISX has 2, and if one is stuck closed, not enough coolant will flow to cool the engine, and bringing the fan on will cool the antifreeze more and lower the temp. Or it might just be sticking and finally opens at a much higher temp.

But I would also be sure you don't have something plugged or blocked in the coolant system too.

This is what mine did for awhile, then it started to run kinda hot on the highway. I started having to turn the fan on manually a lot to keep temps down. Finally one day the temp just would not drop. Babied it into a cummins shop and it was the water pump. They had me in and out in half a day. Covered it under warranty no problem.
There first guess was EGR too.


You might be smelling it from it constantly expanding and filling reserve tank and venting. I started smelling it also but never lost any coolant and never found any leaks.

The other thing that happened to me was the belt tensioner quit working. Since it controls the water pump, perhaps engaging the fan puts it under enough load to tension and then work?

Odd you would mention the belt tensioner. I put a brand new tensioner, and belt on same time the fans clutch was replaced. The part that bugs me; I can actually make the belt slip around the water pump by spinning the fan by hand. It really feels plenty tight, it just doesnt seem that it should slip though...

Water pump was my very first guess. This past week while I was at the Volvo dealer getting a blown out front air bag replaced I asked the service writer guy his thoughts (my mistake lol) about what the problem might be. Basically, I got no help from him.

I guess if it is the water pump heading south, eventually it will start overheating all the time, and maybe weep a little. Will be a lot easier to diagnose when that happens... Volvo quoted me $368 for the pump, and $3.00 for the Oring. Gotta get that extra three dollars for the oring ya know

The tensioner ought to be tight enough that the only way you can spin the fan, is if you are turning the engine too! And I kinda doubt you are doing that. If you can turn it by hand I'm guessing the spring is bad, or they gave you the wrong part.