Cooling system is dialed in and running really well since the head gasket replacement project back in January. Truck has never run better. BUT - out of nowhere (because of course we can't enjoy a problem-free disco) tonight the coolant temps started climbing while at a stop light... 188... 194... 201 202 204 208 210 until the light turned green right as it struck 212, and once we were underway the temps dove right back to the 18Xs. I replicated the problem again at a parking lot and then again once I got home.

Quick info - 50-degree ambient temps, no A/C running, discovered through all this that the throttle body heater is weeping every so slightly.

I tested the fan clutch by giving it a spin right after shutting off the engine. It spun with a lot of resistance. Hard to convey a subjective measurement of this, but when giving it a push, it spins the distance of 2-3 blades, then stops. The clutch only has about 2000 miles on it. New one from AB.

So it has to be air in the system? Perhaps due to that TBH leak? There is the *smallest* gurgle that can be heard through the heater core. I've had air in the system plenty of times in the past when the head gasket was being dramatic, and never had temps rise at idle before. This is a first.

So, possible suspicions are... air in the system or somehow the fan clutch isn't functioning like it should. Thoughts?

 

I would suspect the fan clutch if all else is good.

 

Even though the fan clutch is only a year old (so frustrating, two months out of warranty, of course), I just decided to order the Gates/Hayden situation everyone raves about.

For future searchers:

Dorman 620-112 fan: https://amzn.to/3eEWhs7
Hayden 2991 fan clutch: https://amzn.to/3T5U9Zu

Will report back after installing on Wednesday.

 

DUDE! You have just described to a tee what I just started experiencing- invariably just after I fixed another issue. Except my fan clutch (and radiator and OEM soft spring 180F T stat are only a few months old and maybe 1k miles).

The only thing I can deduce is that as the ambient temps start dropping here, I turned the HVAC temp up to where the heat started to work and now coolant is flowing more in the heater core.

Like you, I assumed this was bubbles as I did get a rushing sound as I shut it off one time this weekend. So I parked it at a healthy incline ad cracked open the expansion tank cap. I’ll take it out today and report back.

 

I too have been experiencing this exact same issue of late. It all started after I completed my Flowkooler water pump upgrade and changed out the fan and clutch to the Dorman/Hayden combo. Really has me frustrated because, like you both are seeing, ambient temps are dropping yet my idle temps keep creeping up.

 

My truck has just about always had this type of behavior. Multiple fan clutches, 180 OEM and inline thermostats, etc. Multiple bleeds. No leaks or coolant loss. I just live with it. For me, it is mostly hot weather and coming off the highway.

 

Man, frustrating. Coolant is always flowing through the heater core, so probably not that? Assuming the cooling system is well sorted out overall, this is textbook example of a bad fan clutch. I'll let you know if that ends up being the case for me. I hope it is? Because I just want this fixed. But IF it's indeed the solution, I'll be so frustrated too that this is just yet another new part that died prematurely. Add it to the list of wheel hubs, water pumps, ball joints, etc.

 

I don't like the gurgling sound described by OP...sign of air in cooling system. I have normal temps and no gurgling after head gasket repair /bleeding of cooling system.

But, easy to tell after you replace the fan clutch if that solves the issue.

 

Its very small, almost unnoticeable, but also the cause is just the TBH…again…

 

One of the biggest reasons I spent so much time researching to find a way to get rid of the clutch fan, was for the reasons you are describing. Rising temps at idle, and heat soaking when turning the vehicle off. Check my signature for how to get rid of that P.O.S. clutch fan, you won't regret it, and it's pretty easy to do...