The heat in my 97 3.9 is also slow to warm up and I have been reading this thread with interest. I think in the spring I will flush the heater core to see if it is full of crud, but today I used a scrap of plywood to block off the lower half of my radiator. It fit in nicely between the bumper and the front of the AC coil.

I am not driving the truck for a couple days since we have ice glazing everywhere here at the moment, but I hope to take it for a spin Saturday and get some idea of whether the truck will warm up faster (it should) and whether the heat is warmer (I am doubtful).

The other thing I've done is avoid shifting into 5th gear for a while. That warms the engine up quicker as well. And it may be just me but I think the heat is warmer when the engine is turning higher rpms.

The high Saturday is supposed to be 38. So I should get a good opportunity to see how it works. I will of course keep an eye on the temp gauge.

 

Blocking off half my radiator seemed to have made no difference. It was 17 degrees when I left the house Saturday to cut wood. When we finished at 1:30, it was up to 34.

I think my heater core needs to be flushed, which I'll get to in the spring. In the meantime, I will live with lukewarm heat.

 

The heater core needing flushing is a common issue. If you get another warm day you can do it fairly quickly with a garden hose.

 

Once you flush out the heater core, make sure you replace coolant with non-silicate brand and use DISTILLED water. Any drinking, tap, spring water (IE, the water you're flushing with) will impart minerals into the system, which eventually collect and form coral reefs in your cores.

 

Amen to that. I have a couple gallons of distilled water waiting in the basement right now. I will probably flush the tap water with distilled, then use ready-mixed coolant to flush out the distilled, and then put the hoses back on.

Just wondering, how long would one leave a flush solution sitting in the core to loosen things up? I guess I just need to follow the label...

 

Not sure which flush you're using. I looked up Prestone, radiator flush which is probably on the top of the list. It said leave in for ten minutes on the internet, but I remember reading a bottle some months ago and it said you could leave it in as an extended flush about three days.

 

Thanks, I haven't bought radiator flush yet, will wait until later in the spring.

 

By then, you won't need the heat!


When you flush the heater core, you don't have to pull the hoses at the firewall. Trace where they go up to the radiator or nearby, pull them both there and flush/back flush from there. Makes it a bit easier.