First time stumped in quite awhile. Maybe someone can help, because truthfully, this ol' van never dies.
It's a 92 Caravan, 3.3 4spd.
I have heat at idle but little to none on the highway. Thermo is working as is the sending unit. Temp guage always reads normal and engine does not over heat, even with the rad blocked with a sheet of cardboard. I have bleed valves at the in/out to the core and am as sure as I can be that there is no air after I flushed it. This problem came before the flush for those about to ask.
Any suggestions would appreciated folks. Thanks

 

Do you replace the t-stat, because it maybe stuck open at times. I had this problem awhile back. Replace the t-stat and the heater worked fine.

 

Yep, thermo is working as it should.
This van gets abused daily and repaired rarely with 585k on the clock. lol
Antifreeze looks pretty clean, but I'm thinking maybe a blockage.
I'm almost afraid to pull any hose clamps but I may have to put some CLR in the heater core and blow it out with compressed air. Best cross my fingers, because it's not getting a heater core. To friggin cold to tear into that.

 

Have you check'ed the heater control valve?

 

No I havent. Someone mentioned that something may be stuck open and letting cold air in while driving.
I'll search the forum for info.

 

The simple diagnosis on blockage is feel the hose in and out of the heater core, they will both be hot! if they are both hot, then you need to look at the heater box like the blend air door.

 

Ya I have a bad feeling this is going to involve the dash coming apart.
Wont be happening as it's well below zero and a foot of snow on the ground. It'll be off to the bone yard and buy another one.
And to think I just topped off the oil and aired up the tires. Most maintenance she's had in awhile. lol

 

Ok. I flushed the heater core after soaking it with vinegar. New Tstat, and after 20 minutes running with the temp guage at normal op temp, the top rad hose is cold, bottom luke warm and the core hoses are both hot. This all before turning the heat on. Headed out to grab a rad cap......and a coffee.

 

Before I left I checked the hoses again and all were hot. Didnt put the cap on yet, for obvious reasons, but I seem to have muche better heat and it stayed pretty decent on the highway. Atleast liveable.
Gotta love an old caravan. From on it's way to the bone yard, with one front left brake, no heat, and a steering wheel that shook your joints, to making it through another winter with under $40 spent. New outer TR, a pre made brake line, thermo and a cap.
Simple solutions after all.
Thanks folks. And a Merry Xmas to all. Time for me to go shopping.

 

so in like less than 20 min, you fixed it? You're amazing