Odd Cooling System issue

[Raoul Ross]

Hello All, new member here. I have a new customer with an odd cooling system issue, the engine never gets to operating temp(~25F ambient). '85 C10 Suburban with a 350 and A/C. The first thing I thought about was the thermostat, so I replaced it. As I refilled the coolant with the engine running, I noticed the amazing amount of flow from the heater core return line to the radiator tank, just under the radiator cap. "Gushing" would be a proper description. I don't think the thermostat ever opens or if it does, very little.

I did drill an 1/8" hole in the thermostat flange to insure no air pocket formed but after seeing the amount of flow going back to the radiator I realized that it really wasn't needed. The description in the service manual says there is constant flow through the heater core, so no valve involved. Dash gauge doesn't go above 100 and the heater hoses are luke warm.

My question is this... I see a "Flow Control Valve" listed at various sites that looks like goes into the intake and is the connection outlet to the heater core. Is this a restrictor, to slow down the amount of flow through the heater core which then would allow the engine to come up to temp? One option Listed Here .

This is really a head scratcher, hope somebody here can help me out!

Thanx,
Raoul

 

[SquareRoot]

Maybe the heater core is sufficient to cool engine at idle at that temp? Once you're under load I would doubt it. 25 isn't that cold. I have a control valve in my VA system. If the AC is on, it blocks the flow completely. It might make a difference in your case. Apparently they are useful or they wouldn't exist.
On second thought now that I looked at link, that's just a standard fitting. I was talking about a solenoid device.

 

[Grit dog]

No, a flow control valve is not what you need. It’s not keeping your truck cold. Not possible or they’d use them as the radiator.
You have an airlock or thermostat upside down or something.
How far you drove the truck and it won’t heat up?

 

[Raoul Ross]

Thermostat *is NOT* upside down. Vehicle was driven 50 miles after running in my driveway for an hour.

 

[Raoul Ross]

That Rockauto link doesn't say it, but the Description says "Water Flow Control Valve; 16MM, ONE DIRECTION FLOW VALVE" I've seen other sites describe it as that also, O'Reillys for one.

 

[Raoul Ross]

Well now that I read the description at O'Reillys it seems I'm on the right track.

"Heater Control Valve; Heating Venting Air Conditioning (HVAC); Water Flow; ACDelco GM OE HVAC Heater Water Flow Control Valves control the flow of engine coolant through the heater core and are GM recommended replacements for your vehicle's original components. The heater water flow control valve is closed when maximum Air Conditioner cooling is selected. These OE HVAC heater water flow control valves have been manufactured to fit your GM vehicle, providing the same performance, durability and service life you expect from General Motors."

 

[ChuckN]

Hello All, new member here. I have a new customer with an odd cooling system issue, the engine never gets to operating temp(~25F ambient). '85 C10 Suburban with a 350 and A/C. The first thing I thought about was the thermostat, so I replaced it. As I refilled the coolant with the engine running, I noticed the amazing amount of flow from the heater core return line to the radiator tank, just under the radiator cap. "Gushing" would be a proper description. I don't think the thermostat ever opens or if it does, very little.

I did drill an 1/8" hole in the thermostat flange to insure no air pocket formed but after seeing the amount of flow going back to the radiator I realized that it really wasn't needed. The description in the service manual says there is constant flow through the heater core, so no valve involved. Dash gauge doesn't go above 100 and the heater hoses are luke warm.

My question is this... I see a "Flow Control Valve" listed at various sites that looks like goes into the intake and is the connection outlet to the heater core. Is this a restrictor, to slow down the amount of flow through the heater core which then would allow the engine to come up to temp? One option Listed Here .

This is really a head scratcher, hope somebody here can help me out!

Thanx,
Raoul

So it’s staying cold…maybe the gauge is inaccurate? Does it get warm enough for you to feel warm coolant through the radiator hose by hand?

One of the recurring themes is to not go strictly by the gauge as sensors/gauges can be not reading correctly.

 

[Raoul Ross]

Yea I don't really go by the factory gauges but the owner sez it works. The heater hoses are luke warm.

 

[Turbo4whl]

Two things, if you can see coolant returning to the radiator from the heater core, your coolant level is low. My guess, the new thermostat is stuck open.

 

[jh86]

What temperature reading is thermostat?

My 86 had a weird low temp thermostat installed for awhile. Low enough the temp based features wouldn’t work.

Any chance too much cooking has been put on it. Eg 4 core with electric fans etc?

 

[Grit dog]

Well if you’re sure it’s the heater core, it is quick to diagnose. Crimp a heater hose and run it up to temp. In 10 min you’ll know for sure.
Presume you know the engine is running cold too by more than the gauge in the dash.

 

[Ricko1966]

Look at the heater fitting at the intake manifold I'm sure I've seen that fitting only have 1/4 inch hole in the center of it,maybe not all but,I never thought there'd be a quiz so I never took notes. I don't think that's causing your problem,but I'd swear some sbc heater fittings are restricted. I'll look at some of my engines when I can.

 

[Grit dog]

And afaik the factory flow control valve was to shut down the heater core for max AC performance. Although too much flow could make the heater core cooler. Happens in low temp fresh water cooling in boards but water isn’t recirculated. Not an issue in cars I’ve ever seen.

 

[SquareRoot]

Disconnect the heater core hoses and replace that part with an LS.