This may be a dumb question but here goes. No heat (blows cold) from my 1995 C4, but all electronics seem to be okay. Thinking maybe the heater core is clogged, or a hose is clogged. Want to replace heater hoses and flush core but don't want to flush and refill entire system. How much fluid will I lose changing hoses? Can I just disconnect heater hoses one at a time and capture fluid in a shop vac or a bucket?

If I can't do this with too much mess I'l have to bring it in and have shop do it at a much higher cost. Your thoughts?

 

Anything is possible. Have you gripped with the heater hoses with your bare hands when the engine is warmed up? They should be hot. The hose from the top of the engine should be the hottest. If not I think C-4s have a vacuum water shut off valve in the top hose going to the heater, they can go bad and stay closed. You heater can pull the heater off and plug the ends with a paper towel and not lose the engine water, you might lose 3 or 4 quarts. Using a catch pan you could reuse it if it still looks good. It is possible to flush the heater core in place if you pull the heater hoses blow out the water and use some radiator flush into the heater core, or use a mixture of TSP (3 to 4 Tablespoons) mixed with water and shoot that in and let that sit 30 minutes or more and flush that out then reinstall the hoses. Check the 1/2in nipples on the engine and make sure they are not restricted but you will notice that when you pull the hoses and plug them. that should give you a few thingss to check.

 

Is the engine itself warming up to normal temperature? If not, then you could have a thermostat that's stuck partially open. It doesn't take much in the winter time for it to be just barely open and prevent the engine from heating up.

 

jsdomino was a little vague on details of the warmth of the engine and heater hoses, and was thinking the heater core was plugged. It would have the same result if the heater hose valve was inop and stuck closed. If he had warm hoses and no heat inside the car that could be actuator or controls, but he believed the actuator and controls were good. Without more information it's a guess.

 

And that's why it's so hard to troubleshoot over the interweb.

 

Yes, to see, hear, touch is always a plus. Most of the time.

 

Thanks I'll check.

 

Howdy JsDomino,

I just went through this exact problem around Thanksgiving. It's documented in this previous post here on the forum: https://www.corvetteforums.com/forum...er-pump-20818/

I replaced the heater core because it was leaking, but even after replacement I couldn't get good heat. I deleted the shutoff valve after it started leaking, but found that it had been stuck in the open position. I think these default open unless the A/C gets turned on, but yours is new enough I doubt it even has the vacuum shutoff. I then went around in a few circles, thinking it was the water pump or the thermostat. As it turns out, the thermostat does NOT control water flow to the heater core. But, as 73Shark noted, if it is stuck open it would have a helluva time ever coming up to temperature.

The source of my problem turned out to simply be air in the system. It was kind of confounding because when I checked the radiator cap it would look full, but I rarely had heat and on startup I would sometimes see a low coolant light. It was then that I realized that the radiator is so low on these cars that it is barely even the highest point in the coolant system. I bled the system by jacking up the front passenger's corner of the car and filling/starting/shutting off/filling over and over again until I got most of the air bled out and the car stopped taking any more coolant. It took well over a gallon of coolant after it had been appearing full on the ground! After I did that, I finally had reliable heat.

Three weeks later, a lady stood on her brakes as I was trying to get behind her on a two-lane highway and I spun out and totaled the corvette avoiding a collision with her or the car in the oncoming lane. I think I am one of the few people who can say they rolled a convertible corvette and walked away unscathed, but it was quite a bummer after doing all that work to fix the heater core among other things. And because now I have a wrecked corvette.

TL;DR: If you didn't already figure this out, try bleeding the air out of the system and see if it is just low on coolant. I think the heater core is one of the last channels to get fluid pressure when there isn't enough coolant.