Heater issue?

[SUBURBAN5]

They had different factory temps. I'm just curious what temp your running.

 

[Schurkey]

they talked me into this “failsafe” brand. Supposedly if it fails at all it will stick open no matter what.

That is NOT how they're advertised. Lots of folks--including, apparently, the folks retailing them--are afflicted by a lack of logic and an excess of wishful thinking. I see this statement fairly often in regard to the "Failsafe" thermostats.

A "failure" cannot be promised to happen a certain way. That's the nature of "failures"--they're undesired operation or non-operation. The "Failsafe" thermostat is not guaranteed to "fail" in the open position.

The advertising is that if the engine overheats for SOME OTHER REASON THAN THE THERMOSTAT, the thermostat will lock open. This is totally useless, as any other thermostat would be fully-open as long as the temperature was high enough; and after it cooled down, (hopefully the overheating problem gets resolved) it'd close so that it was still usable. The "Failsafe" thermostat is scrap-metal after it locks open.

MotoRad Fail-Safe® Thermostats

Motorad Fail-Safe Thermostats, are designed to prevent engine overheating & provide peace of mind on the road. Upgrade to Motorad Fail-Safe Thermostats for dependable temperature regulation and worry-free driving.

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When overheating is caused by a deteriorating cooling system part, the fail-safe has a secondary stroke that activates a precision engineered piston. This automatically locks the valve into a wide open position to allow coolant to circulate freely.

Note that once the fail-safe thermostat has locked in the open position, it cannot be used again and must be replaced.

Think I should change it out?

Yes. When it fails. But there's no reason to replace it "just because".

 

[gbiddlec]

That lead me to looking at the heater hoses, theres a little valve right before the fire wall with vacc lines running to it. I found a vaccum leak there, fixed it and still no heat.

That valve applies vacuum to shutoff the flow to the heater core at the crossover valve, when you turn on max A/C. Unless max A/C is on, it should be fully open. the vacuum line should run to a solenoid on the firewall and then on to the intake. I don't think this is the issue. Make sure you have a 195 T-stat, I tried a 180 in my Suburban and just couldn't get it hot enough.

 

[1998_K1500_Sub]

That valve applies vacuum to shutoff the flow to the heater core at the crossover valve, when you turn on max A/C. Unless max A/C is on, it should be fully open. the vacuum line should run to a solenoid on the firewall and then on to the intake. I don't think this is the issue. Make sure you have a 195 T-stat, I tried a 180 in my Suburban and just couldn't get it hot enough.

And for the record, that solenoid operated vacuum valve seems to get plugged and fail. I've pulled them out and cleaned the vacuum passage (e.g., with Brakleen) to restore them to service.

The coolant crossover valve's vacuum motor might, I assume, fail as well.

So if you start checking those parts for proper operation, be aware.

I thought they only put those "max-AC" operated coolant crossover valves on the Suburbans and crew cab models but, if you say you've got one, then you've got one.

 

[east302]

I forgot to add the t-stat is about a month old.

Did you bleed the system after installing the thermostat?

On the actuator, the notched silver dial rotated smoothly between (roughly) the 11 and 1 o’clock positions? There should be marks on the housing that correspond.

Adding to what the others said on the valve on the heater hoses, there’s a rod/plunger at the bottom of the valve which is connected to the valve butterflies. Engine on and temperature set to heat, push up and down on it and it should move with moderate pressure. Compare to engine off and the effort required should be pretty damn close if not the same.

When the valve is closed (panel temp dial is set to MAX detent) the solenoid is energized, vacuum is applied and the rod is up or pulled inside of the valve. It won’t move.

The valve is specific to Tahoes and Suburbans, closing when the “max” detent is selected on the temperature dial. Alternately, pull the vacuum hose from the valve and see if it makes a difference.

If it does or if that plunger doesn’t move when the dial is not set to max, then the solenoid valve on the firewall may be energized somehow which goes back to the panel itself. See if you have 12V on the connector to it in that case. You shouldn’t unless it’s set to “max”. I’ve had a (dorman dirty word) panel that was brand new and kept that thing energized regardless of what it was set to.

If the valve is closed and you don’t have voltage to the solenoid or if that plunger doesn’t move with the engine off, then I’d suspect a bad valve.

 

[Yngwytprik]

Did you bleed the system after installing the thermostat?

On the actuator, the notched silver dial rotated smoothly between (roughly) the 11 and 1 o’clock positions? There should be marks on the housing that correspond.

Adding to what the others said on the valve on the heater hoses, there’s a rod/plunger at the bottom of the valve which is connected to the valve butterflies. Engine on and temperature set to heat, push up and down on it and it should move with moderate pressure. Compare to engine off and the effort required should be pretty damn close if not the same.

When the valve is closed (panel temp dial is set to MAX detent) the solenoid is energized, vacuum is applied and the rod is up or pulled inside of the valve. It won’t move.

The valve is specific to Tahoes and Suburbans, closing when the “max” detent is selected on the temperature dial. Alternately, pull the vacuum hose from the valve and see if it makes a difference.

If it does or if that plunger doesn’t move when the dial is not set to max, then the solenoid valve on the firewall may be energized somehow which goes back to the panel itself. See if you have 12V on the connector to it in that case. You shouldn’t unless it’s set to “max”. I’ve had a (dorman dirty word) panel that was brand new and kept that thing energized regardless of what it was set to.

If the valve is closed and you don’t have voltage to the solenoid or if that plunger doesn’t move with the engine off, then I’d suspect a bad valve.

I did bleed the system, it got a new radiator at the same time. And didnt have issue with the heat until i replaced the climate controls, blower motor, and resistor. But ever since monday morning it blows good and hot so who knows whats goin on i havent changed anything.

 

[E-gads]

My son in law installed a HVAC control panel bought off of Amazon and had the same problem. I went through everything and couldn't find anything wrong. He had just acquired the Tahoe from me and it had been sitting for over 5 years so we assumed it was an existing condition , plugged heater core, bad heater valve, etc. I went to the blend door actuator that's near the fan that blocks off the heater core when cooling and watched it operate. Didn't seem to me that it was moving far enough. Being that it was going to be a pain to replace I put in an old unit that I had just to test it and then miraculously he had heat. He ponied up for the AC Delco controller and all is good. I would consider sending that unit back to Amazon. Funny to see this post as this only happened two weeks ago.

I learned the hard way a long time ago that just because something is new, doesn't mean it works right. That has become more true over the last few years with the poor quality of aftermarket parts these days.

 

[1998_K1500_Sub]

A couple of pictures of the solenoid-operated vacuum valve and the coolant crossover valve, attached, for reference.