Robert.L.Harris

Apologies if I ask something dumb as I'm new here and new to my C3. I did search but couldn't narrow the issue.

I have a '79 C3 in relatively stock condition ( Dad said he kept it stock or bloody close but finding a number of things aren't what he expected ). At any rate, I'm out here in Denver, the roads are clear but it is getting cold. I took her out yesterday and the temp gauge never got over 110 even though she ran perfectly well. The heater output never got above outside air temp either. The radiator is good and is full of anti-freeze as is the overflow.

Is this normal or is there something odd I should look into? I've never seen an engine run for 45 minutes refuse to warm up.

dan1495

That isn't normal. It sounds like there is no thermostat or if there is it may may be stuck open.

Robert.L.Harris

That could be a possibility but I just had my mechanic replace the water pump Friday. He us usually 100% on the ball and I would think he would have checked that while he was in the area.

Know a good/easy way to check it other than pulling it and visually inspecting? It looks like it should be easy to get to but getting in to see him might be problematic just due to my schedule.

Alan 71

Hi RH,
Welcome!
First Posts!!
Chilly in Denver!!!
Here's the coolant flow direction for the cooling system.
Upon start up the upper hose stays 'relatively' cool until the thermostat opens; then it increases in temperature.
Lower hose warms more quickly.
The hoses to the heater core should become warm/hot to the touch as the engine coolant warms up. Note direction of coolant flow for those hoses too.
Regards,
Alan

flyeri

He certainly could have changed the water pump and not removed the thermostat housing. I think I would replace the thermostat and see if that solves the issue.

Robert.L.Harris

OK, a quick youtube search shows the thermostat is easy to get to so I'll pick one up on the way home.

Thanks.

CanadaGrant

Don't forget to get a gasket with it.

7T1vette

Clean both surfaces [well] of all residual gasket material and/or sealant. Install stat with temp coil/sensor on the 'manifold' side; the stat flange should fit into the undercut on that manifold face. Install the gasket on that face AFTER the stat is installed. If you put sealant on the gasket, just put a thin wipe of it on both sides and let it nearly dry. DO NOT USE A SILICONE SEALANT FOR THIS JOB; use a gasket sealant like Permatex No. 2 sealant. Put some sealant on the last few threads of both bolts. (This will prevent any wicking up of coolant via any porosity in the manifold casting.) Install bolts to 28-30 ft-lbs torque.

Robert.L.Harris

So last night, my son and I replaced the old thermostat with a new one rated for 160. The old one looked perfectly fine ( closed and straight ). However when we took her out for a test drive she did actually warm up 1/4 of the way ( with 220 at top middle ). The heater never did warm up on our feet though.

flyeri

You really need a 180 or up to 195 degree thermostat. 160 doesn't let the engine get up close to optimum temp a street engine.

billschroeder5842

There is really no advantage to running a "cooler" thermostat unless you are racing your car.

All systems are designed to run on a 195 stadt. You could accidentally send false reading to the system for Choke, ERG, emissions et. You coud possibly throw service engine light.

Plus, you heater does not like a cool stadt.

Robert.L.Harris

Great info, thanks. I've never worked on anything other than a Jeep so there was only the one thermostat. It seemed to make sense when the parts guy ( who's normally good with my Jeep ) said the cooler one would be better for the larger engine and it's performance. Yes, I've got the manuals for the car but haven't gotten that far in yet.

I'll get a new thermostat today and install it though I'm not driving with the inch of snow on the ground.

lvmyvt76

why did the parts guy sell you a 160 stat??? his computer should of told him you needed a 195.

Robert.L.Harris

I was looking at the screen and it did list 2, 160 and 180, no 195. He may be used to the kids who race the little sportsters around town and think that that was my goal. I'll try a different parts store this morning.

Many thanks guys, very knowledgeable and friendly forum.

corvetero

Remember to bleed out the air from the system

speedreed8

the heater water vacuum valve in the heater hose may be stuck closed also not allowing water flow to the heater core.

Robert.L.Harris

I replaced the thermostat with a 195 rating and it heats up correctly. I'm still not getting any heat though. My mechanic said he replaced the vacuum valve when it was in for Cat installation though I didn't verify. I can give him a call tomorrow, but any thoughts of anything else which might be worth looking at?

Metalhead140

Are the heater hoses getting hot? If coolant is flowing through them then they should be a similar temp to the top radiator hose when the engine is up to temperature.

Robert.L.Harris

OK, I took her out for a run tonight. With the 195 in it's holding that on the guage but it's still blowing cold air ( slowly ). I put my hand on the hose going to the vacuum switch and it's warm, seemed the other side of the switch was as well ( be VERY careful of the headers, ouch ).

Thoughts on where to look next?

flyeri

Is it (hose) as hot on the heater side of the vac switch as on the engine side? Is the return hose from the heater core hot? Maybe the vac switch is only barely open allowing enough hot water to warm the hose but not enough to heat the cold air moving through the heater. Kinda guessing here. Here is what I would do now. I would get a short piece of heater hose and plug one end. Slip the heater hoses off the engine and put the short plug piece on at the water pump to keep water in engine. Then I would attempt to blow some air through the heater system. Not sure if the vac switch uses vac to open or close. That will blow some of the water out but you need to determine if you have a restriction in the hoses or core. Sound like you are getting some flow but may not be enough to heat the air so that you can feel it.