1998 c1500 w/t running cold experts please!!!

[Integra_boomer]

ok i am in dire need here. my understanding of the coolant system is just a small drop in the bucket right now. the truck has the 4.3 vortec v6. Heres the problem: It runs cold and no heat at all! and also the temp gauge will get up to 195 sometimes for 8 seconds then drop back down to 140 degrees. 90% of the time it runs 140. operating temp is 195.. heres the trouble shooting i did. first off runs cold and no heat so first obvious thing i changed was the t stat. no change! even checked the first one by dropping in in water @ 200 degree and it opened. so then i came to the conclusion that there could be two issues the gauge is out of wack bc of bad sensor and the heater core is out. well i replaced both coolant temp sensors. one on the neck an one on the block. one for the ecu and one for the gauge itself. still no change. so about right now im really irritated! there is not much other than a t stat that can male a motor run cold. another observation i made is that one hose going into the core is hot and the other is cold. heater core bad? even if heater core was bad motor should still be warm correct?? another thing i will add that i think is not relavent but never know is the truck misfires. but plugs were shot when i got it so replacing one thing at a time on the ignition system as i diagnose that matter. main concern is why this damn thing is running cold!! ive dumped 60 bucks in parts and still no closer than i was when i bought the truck.

[95legwagon]

heater core plugged? bad temp gauge also maybe? pick up a chiltons for checking these things.... not sure if you can test the gauge with dmm or not.....plugged heater core would get you cold air ( no heat) and the antifreeze line might have a bypass before it reaches the core but i really have no idea on that one to be honest

[ImaNoob]

I would check for blockage , try flushing the core.

[fox_racin4]

If one side if the line is hot on heater core and the other is not...you need a heater core. IIRC they are way up in the dash.

My truck runs cool, but i still get heat from it. When warming up My trucks temp will go up, then once t-stat opens i can watch the temp drop.

[Integra_boomer]

even if heater core is plugged or bad the engine should still run at operating.. and as i stated. i replaced bothe sensors. one for the gauge and ecu

[fox_racin4]

It would yes. Maybe the engine just runs cool.. How are you getting these readings?

Are you driving it or letting it idle?

[BassJunkie]

random question but when you replaced the t-stat did you happen to replace it with a failsafe t-stat? my car did something similar when i used a failsafe thermostat, it stuck open, they're junk imo.

[Integra_boomer]

driving. idle. doesnt matter. i know when a car should be warm. you could drive it for an hour and still no difference. im not sure i think it was a duralast. but i here alot of ppl say faulty t stats from parts store r common

[Nico Shull]

It does sound like your heater core may be plugged. A nice easy way to check is to disconnect the heater hoses going to the core. Find an old 5/8" garden hose and cut the end off so you can attach it to one of the heater core pipes. Slowly turn on the water and see if it flows out the other pipe of the heater core. If not, try hooking it up backwards and "backflushing" it. If there's still no water flow, you definitely need a heater core.

Another option I have personally run into on a Chevrolet Yukon with a 5.7 V8 (Just 2 cylinders added to your 4.3 V6) is the impeller on the water pump became separated from the impeller shaft. So, the coolant flow to the heater core was non-existent unless RPM was above 3,000. Upon installation of a new water pump, the coolant flow to the core was completely restored.

As for low temperatures, many things could be causing it. I would start with a fresh new thermostat. For the price of them, I'd even go to a GM dealer and get one from there if you can.

An issue we often have up here in Canada during the winter months is the engine simply doesn't produce enough heat to overcome ambient temperature. I doubt you're experiencing those kinds of temperatures, however.

Hope some of this helped.