Overheating. Help please

[Kukailimoku]

Hello.

I have an odd overheating problem.

Symptoms:

Temp fine at highway speeds.
Overheats at stop-n-go, rush hour commute traffic.
Upper radiator hose is very hot, but the top of the radiator is flat out cold. The top half of the radiator is cold.


Some additional info that may or may not be relevant:

Once in a while, maybe once a week for the past few weeks, the water pump spooges out a cup or three of coolant. I find it under the truck in the drive way. Not every day not every drive though....
Even odder still is that the reservoir is full and even though some amount of coolant has been lost, nothing is sucked out of the reservoir to replace the lost fluid.
Also, the heater (hot air in cab) takes a long long time to kick in, bit eventually does, so it's not entirely blocked, but is oddly slow to heat up (compared to normal)

Background:
Both the radiator and the water pump have been changed within the past three to six months (separate incidents though).

2005 1500 SLT 4x4 quad cab. 252,000 miles.

Ideas?
What are the usual suspects?

Many thanks.

 

[atom13]

Changed T stat? It could be air trapped in the system.

 

[CincyZach]

Has the thermostat been changed?

 

[Kukailimoku]

Yes, the t stat was changed when the water pump was changed. Interesting idea folks....
So, how would air feet trapped by the t stat being changed, and how to get it out?
I don't get how the t stat can trap air (not arguing your diagnosis, really I wouldn't know how that would happen so I'm asking)
Would simply running the engine for a bit with the radiator cap off, do the trick to let trapped air bubble up to the top and out????
Thanks.

 

[Ballistic308]

It’s your fan clutch.

 

[JohnnyMac]

All of the above are very viable suspects. I think the T-Stat and the air in the system are actually two different issues, unless I guess if the air is trapped at the T-Stat and not getting warm enough to open it. The thing I find odd is that it is not sucking the coolant back in after it pushes it out to the overflow tank, which would point to a leak somewhere. A leak wouldn't allow a vacuum to be produced when things cooled down to suck the fluid back into the radiator. Could be a couple things. A bad fan clutch which causes it to over heat and a bad radiator cap that isn't working at the right temp. If your new radiator came with a cap, and you still have your old cap, try putting that on.

 

[LoneWolf3574]

Probably a dumb question, did you change your radiator cap when you changed your radiator out? It should be a 16psi cap if I remember right.

 

[Karlsweg]

Get a new radiator cap. Pull truck up a slight incline, turn heat on high and idle with cap off. Add antifreeze mix if fluid level drops. You should see when t stat opens . After it opens, any trapped air will burp itself out. Top off radiator and put the new cap on. Fill overflow tank up to the max line when hot level.

 

[Kukailimoku]

Bump, and also new info:

1. the temperature swings really quickly. Literally within one minute or less. (presuming it's already at normal operating temp been driving for awhile). If I come to a long light, or prolonged stop-n-go traffic, i can actually watch the temp needle move higher. When I break out and get above 40mph or so, I can watch the needle move lower. I'm not talking about i looked away for a few seconds looked back and it moved, like a clock's minute hand does. I mean i can actually see it move as it swings. that fast. Does that mean anything, confirm or deny previous suggestions?

2. Last night when I shut off the engine I quickly felt the upper radiator hose. I could feel bubbling/gurgling - couldn't quite hear any burble because of ambient neighborhood noise but definitely beyond a doubt felt the bubbling in the hose.
Would the coolant burbling like that (immediately after engine shut off) be a normal thing or does that confirm some of your suspicion that air is in the system?

WRT radiator cap: (Edit) Yup, it is the old rad cap. Will change that today (cost is negligible so no real waste there even if that aint the cause).

WRT fan & fan clutch: Yeah, I too logic'd that the fan might be a culprit as well. Because highway speed forces ram air through radiator the temp is really cold, and when stationary it gets really hot (as if the fan aint pulling air through the radiator). However, I looked at the fan last night idling in the driveway and the fan was definitely spinning fast (to my eye). Can it be possible that the fan is spinning but not fast enough/not at the supposed to speed?

Karlsweg I will do your technique after I get more feedback from the members to my added information first though. (btw, i love that gun control in your signature.)

 

[Karlsweg]

Sounds like a bad clutch fan also. With the engine running you can take a rolled up magazine or news paper and carefully touch the fan with it. If it stops the fan, the fan clutch is bad. I had to do this to diagnose my fan clutch and replaced it with a Napa heavy duty unit. But if it’s gurgling, there is air in the system.

 

[atom13]

I’m not familiar with your motor or engine configuration. I know that older Chevy trucks were terrible to bleed all air out of coolant system.

Your fan clutch is probably bad or on its way out.

I would search you tube for bleeding procedure.