Coolant Temp/Heater Performance Issue

[Ironhead]

Background: I have a 69 GMC pickup with the 350 and TH 350 combo. Very nice survivor. I also have a 98 Silverado with the 5700 Vortec/4L60E combo.

The 69 warms up fast, and the heater toasts the cab in just a few blocks of driving. The 98 takes forever to warm up, and the heater never really gets all that hot. So, I drained the cooling system on the 98, flushed the whole system, put in a new AC Delco T'Stat, and filled with a 50/50 mix of green antifreeze and water. To do the flush, I used one of those T-Fittings that goes in the heater hose, and hooked up a garden hose with really good pressure.

Did not make any change in the coolant temp or heater performance. My temp gauge goes to a little bit above the one-third mark. Same with both T'Stats. It takes about 3 miles before any heat comes out of the heater at all.

Suggestions would be appreciated on this issue, and I thank one and all for any help.

 

[Calvinator]

With engine hot, check the two heater hoses going to your heater core. They should both be hot. if one hot, and the other cold, your heater core is still plugged.

Lots of youtube videos on this subject and good reference.

I don't have a 98 model year truck so I might be wrong. But, I think the coolant supply line from the engine goes into a T connector. The T connector feeds two lines to your heater core and then one is a return line to radiator. I think the T connector has electrical switch component. Switch may have issues. I could be wrong, but I saw this T/switch for 1996+ trucks when I was researching my 1995.

And for reference, I just cleaned out my heater core. I was getting 84 degree temps in the cab. After the heater core flush, a nice toasty 145-150 degrees !