Ok, this one has me puzzled.

98 GMC Jimmy V6 SLT

Cooling/Heating problems galore. It all started back a few months ago when it started to over heat. I checked the coolant level in the overflow and it was fine. Checked the raditor and it was emtpy... ok getting strange now. So.. long story short, 2 flushes and a new water pump and thempstat later the car is now running fine, but the heat is only luke warm. I also get a strange "water gurgling" sound when I step on the gas good. Car temp shows normal level, running nice. Hoses are hot so I know the fluid is right. Uncapped it and checked for air bubbles by letting it run and rev for about 15-20 minutes and presto, the heat is hot.
Now, I think I have this thing licked and put the cap back on and go driving and the heat gets luke warm again, not hot like before. The only thing I did differently is put the cap back on. So I take the cap back off and it's hot again... Is there something in radiator caps that can go bad? This one has a spring on it, but it's almost like the thing is acting as a themostat??? My next step is to get a new one and test it, but I'm I barking up the wrong tree here? And what is that wierd sound??

 

You are building an airlock in the radiator. Replace the cap. It is not letting the pressure off when it is supposed to.
Hope this is helpful to ya,
Billy

 

The radiator cap's job is to maintain a constant pressure which raises the boiling point of the coolant. It wouldn't hurt to put a new one on. They do go bad. Are you sure you didn't reverse the hoses on the heater core (or the water pump)? The sound your hearing is an air pocket. Is it coming from the heater core?. You can try putting a restrictor in the heater core outlet if you don't find another problem. That will slow down the flow in the heater and keep it full.

 

That was it all!! Replaced the radiator cap and heat works great. I still hear a bit of gurgling, but I bet it needs to work itself out. Thanks for all the imput, go figure... a cap...

 

Well all, it appears that I spoke to soon. Heat (or lack of it) issue is back. New cap seemed to fix it for a few short days, but now it's back at the same thing. I've also just tested the car with the cap off again and plenty of heat. The hoses heat up nicely, I blew air through the recovery tank hoses and they seem fine. Any other suggestions?

 

One more thing, I seem to get a burst of heat if I accelorate fast.

 

i believe your heater core is clogged.many vehicles equipped with dexcool have this problem.maybe take both hoses off and try to force water or air through to verify.if you can get most of it out you may not have to change it.