The a/c works just fine. But when I turn on the heat,It blows cold. It doesn't seem like hot water is going through the heater core. Any suggestions ??

 

Check your passenger floor board. If its wet, its your heater core. Hard work but its do-able by your self. Its under the air bad in the passenger dash in a block box. Take the seat out, lay on your back and start unbolting

 

given your junior member status, I am guessing the car is new to you, so first of all, congrats on your new 'to you' Vette. You'll likely spend alot of time here and if you don't have a set of FSMs, do get, worth their weight in gold.

Suggest inspecting the coolant hoses which run to the firewall, one runs directly from the water pump, through a plastic connector/restrictor along the wheel well, and the other one to the bottom of the pressurized recovery tank (where the raditator cap is).

Check these for being disconnected or bypassed and also check for being hot (at least the one from the water pump).

the 94s do not have a shut-off valve in the coolant flow to the heater core, so it runs through it all the time, so if no warmth felt from the return/exit hose, could be the heater core is completely clogged.

If by contrast the hoses both feel hot, then it could instead be the 'mixing' door in the dash (directs air through or around the heater core). Sometimes this can not operate due to vacume hose problems and or other issues -- but do a search, plenty on it here...

 

The blend door is electronically controlled ; vac only affects the vent positions

 

The floor is dry, for now. Hopefully it's just clogged. I will try to flush it out. Wish me luck

 

Thanks on the congrats. Just got it 2 months ago. The hose from the water pump is hot half way up. But the other hose is cold. I guess the core is clogged. I will try to flush it out. Hopefully I won't need a core. Thanks

 

My car is a 94> I had the same problem- no heat. The heater core was cloged, and my shop was able to unclog it by reverse flushing just the heater core. They spend quite a bit of time on it, but still cheaper than replacing it. You will hear that there is a risk of damaging the heater core by adding air pressure along with the water , but that is what they did as a last resort and it worked.
Apparently these years are prone to plugging the heater core.
I have been sure to drive the car in cooler weather and use the heater , as I think it may help to keep coolant circulating thru the heater core.

 

Thanks, I'm going to try to flush it tomorrow. Hopefully I will get lucky like you did.

 

Great news. I flushed the heater core today. I know have heat. So glad I didn't have to replace the heater core. And the rug is still dry..

 

Thats great..what steps did you take to flush core? my problem sounds spot on to yours..thanks, Dennis

 

I disconnected the curved hose that goes from the top reservoir to the heater core, Then disconnected the other hose from heater core to water pump. There was something that looked like a check valve on that hose about a foot from the heater core. That's where I disconnected it. You are going to loose the anti freeze from the top reservoir. Then I used my garden hose and shot water in the curved hose that goes right into the heater core. This will flush the heater core right out. Make sure to point the other hose down so it doe
doesn't get all over the engine. Make sure it doesn't spray all over the spark plug wires. Don't want to wet that optispark..

 

Thanks for your reply,good info.i will give this a shot soon,ohio gets cold..lol

 

This morning was in the 40's and a couple of miles into my usual drive to the lake I noticed no interior heat in my '94 and the water temp gauge was climbing fast. I stopped, found the upper reservoir gurgling and the overflow tank full of coolant. After I added water at the upper reservoir the temp returned to normal range and heat again flowed from the heater.

theadmiral94 says "94s do not have a shut-off valve in the coolant flow to the heater core, so it runs through it all the time, so if no warmth felt from the return/exit hose, could be the heater core is completely clogged." I assume my problem is a clogged heater core and will try Erniep's method to flush the heater core but if anyone has any other ideas I'd appreciate them.

Thanks in advance.

John

 

Sounds like it is time to replace the thermostat, AustinJohn.. I used that Prestone flush on my 92 and it caused my radiator to leak from the seams. Never use chemicals to flush (at least a 92 and up) the system.. It "was" cold this morning. But I rode my scoot to work..

 

The only things I can add is to not flush with full pressure. Older cores do not like it. Flush in both directions until water runs clear.

When I got my 94 in 03 I had to do a flush also. But I also found out it had a tendency to clog again probably due to crap in the block. So I flush the core about every year and flush the whole system every 2 years. It flushes pretty quick now.

First time I had to do it 12 times before it cleared while reversing the flow is was so bad.

 

Thanks folks for the great advice. I'm going to do it first thing tomorrow and I'll report back. This part of my maintenance got away from me as my last backflush was '08.

John

 

Well flushing didn't (at least not yet) do the trick. I flushed and backflushed the heater core but there didn't seem to be any resistance and very little debris came out. I flushed the rest of the system, headed out for the same drive as yesterday; temp started at 175º, paused at 195º, settled at 205º and then all of a sudden started rising rapidly to 250º (all digital readings). I let it cool, added water to get home, refilled and reburped and it ran up from 185º and settled at 205º (I was chicken to try another road test).

Idling in the garage for 10 minutes with the ambient temp at 70º (water temp at 205º and oil at 190º) the air out of the heater vent with the control dialed to 90º is 110º (I realized with 20-20 hindsight I forgot to reach down and check whether I was still getting heat today when the temp rose so abruptly).

The stat is 4 years old, the radiator and upper reservoir are 3 years old (the car is my daily driver) as are the hoses. The water pump is also 3 years old and as the stream from the top of the radiator into the neck of the reservoir is strong, I assume the water pump is doing its job. The car has always run hotter than other folks claim but yesterday's overheating was a first since I did my system overhaul.

I'm baffled (and reading through the Forum know I'm not the first). I wonder is it is indeed a suddenly closing stat as mixalive suggested? My stat is 180˚ stat but not a fail safe version which upon failure will stick in the OPEN position. I found another thread started by the admiral94 in which he tests stats and believe my next step will be a new stat.

Appreciate the help.

John

 

Yep. Sounds like thermostat issues. Appears to be sticking open one day, and closed another day. Cheap fix.

 

Installed a new stat this morning and first results were great altho later were puzzling. Here are the details.

Despite theadmiral94's misgivings about the Stant Super-Stat I couldn't find an AC Delco in town so installed the Super-Stat #45218 and headed out on the same loop as the last two days. Ambient temp was 63º and temp rose through 195º and seemed to settle at 201º. Then it started "cycling" and over 10 miles of suburban stop'n'go driving it cycled perhaps 4 times down to 194º and up to 201º.

I parked for an hour, drove another 5 miles in stop'n'go driving and same cycling, perhaps twice. Parked again for an hour and headed home with the first 2 miles again stop'n'go driving and the last 3 miles 65-70mph. Strangely in the latter part the temp rose steadily to 220º but as soon as I turned into the neighborhood and resumed slower stop'n'go driving, the temp quickly fell to 194º and never cycled higher.

Saturday mornings I always drive 50 miles out to the country (to Blanco - mixalive will know where that is) and that will be a better test of the stat and system at higher sustained speeds.

John

 

Sounds normal. Does the heater work? And yes, I have been to Blanco a few times. I use to live on Blanco Rd. in San Antonio.