Heater Problems

[tjdude]

I have a 83 K5. I started this winter with no heat. I've been working on it until now. I am about ready to throw my hands up. If anyone has any idea I would appreciate the heads up.

I started with the thermostat. The PO must have taken it out because it didn't have one when I opened it up. I installed a 185* thermostat. This caused the engine temp to go up to 230+ so I pulled that and replaced it with a 160* thermostat. It now runs at 210* (or so the gauge tells me). Still no heat.

Next, I can tell there is no circulation through the heater core because both hoses are cold. It must be the heater core right? I replace the heater core and the connecting hoses with the 5/8 and the 3/4 hoses. I did make sure all of the flaps on the inside of the box were working correctly and my vents and defroster seem to be working as they should. STILL NO HEAT.

Finally I replaced the vent cap thinking it wasn't holding pressure because the top hose was a little soft. It is now nice and firm no problems there. STILL NO HEAT!!

The coolant looks fine. nothing floating on the surface and it is nice and clear/green just like it comes out of the bottle.

I did use a spill free funnel to purge the cooling system any time I opened up the coolant loop. There shouldn't be any air in the lines.

So that leaves me here. My only guesses are 1. water pump impeller failure (its not leaking) 2. Clogged/bad radiator (truck doesn't overheat at idle) 3. blown head gasket (maybe that's why the PO removed the old thermostat?)

Any ideas from anyone? Am I overlooking something? where should I start?

 

[blazer74]

Blockage or improper routing

 

[blazinzuk]

Is this a gas motor? If so your problem lies elsewhere. 185° thermostat does not equate to a 230° operating temp. You got an issue with the cooling system in general. Find that problem I bet it fixes the heater issue.

Now if its a diesel......... Welcome to winter

 

[tjdude]

Just a 350. I have no idea where to look for a blockage. I guess I could start by flushing the radiator? I've never seen a heater core just stay cold like this before.

 

[diesel4me]

I've watched my friend flush out many heater cores at his shop the past few months,on customers cars with poor or no heat complaints..
After he made sure the heater controls were actually functioning,and moving the blend door from hot to cold..

Most of the vehicles had coolant that looked fresh and green--till he applied the hose to the heater core..
A lot of them had such peukey looking rust and crud come out when he applied the garden hose to the hoses and reversed the flow a few times,we wondered if the core was going to leak like a seive later !--but that cured the poor heat trouble..some of the vehicles seemed like someone had used radiator sealant at one time,some evidence of it came out with the brown milky coolant..

Last saturday when I was at his shop,he had a late 90's or so Chevy pickup with a 4.3 in it that had "poor heat"--the owner tried replacing the thermostat himself and flushed the heater core,then gave up and brought the truck to him..along with a "good used" radiator..his original looked like it had barnacles in the cores and ready to leak from corrosion,and with the truck fully warmed up,a heat gun read the center of the radiator was much colder than the sides,he assumed it was plugged up with crud,so my friend installed the radiator and that cured the no heat problem..

My diesels have excellent heat,provided you run the engine a good 15 minutes or so idling,or put a load on it driving it,they'll warm up in 5 miles or so like a gas motor...the only time I have noticed the heat was not as warm as I'd like it was in extreme frigid conditions ,like under 10 above with a stiff wind blowing--if you idle the truck you'll notice the heat will be "warm" but nowhere near as hot as it'll be driving along...(My VW diesel did the same thing--diesels just run cool at idle)..

I've never looked to see if it even has a thermostat in it,it acts like it does going by the temp gauge, and its never overheated,so to avoid creating a headache by attempting to remove the housing and risk busting the bolts off in the aluminum crossover tube,I just assume not disturb it !..

If someone changed the routing of the heater hoses you may not get good flow through the core--the rule of thumb is one hose has to go to the water pump or radiator core,the other to an intake manifold coolant port...

 

[tjdude]

Thanks for your reply. I will report back with results from the flush.

I am probably going to drain the coolant then fill the whole thing with 1 gallon of vinegar water solution heat it up purge the system with that then let that sit for a day or so. Hopefully that will get it cleaned out.

If that doesn't work I'll just replace the radiator. I'll try the 5 dollar fix first though.

 

[blazer74]

Supply to the heater core from the intake manifold (this also acts as a bypass untill the thermostat opens) and return to the rad or top of waterpump either one.

If one hose is to the waterpump and one hose to the rad you won't get heat.

Fittings on the intake manifold or waterpump/rad plugged up?

What's the condition of the rad?

 

[tjdude]

That's the problem! one is on the water pump the other is on the rad. I guess both sides are positive pressure? As for condition... nothing on the k5 is what I would call "good" condition.

I cannot get the plug out of the intake manifold. Is there somewhere else I can route the heater hose? I would like to keep one side on the radiator the other side should go where?

Thanks again

 

[blazer74]

Manifold is the pressure side, going to have to find a way to get the plug out without downing your vehicle.

 

[dyeager535]

And install a 195* thermostat. As you've found, thermostat governs minimum engine temperature, not maximum.

Not sure what tricks to use to get a plug out of the intake, heat (oxy/acetylene torch only)might ruin gaskets that are close? If there is enough protruding, welding a nut to the plug will give you something to put a lot of leverage on.

Think I'd prefer heat in this application, with coolant in the engine I'm thinking the heat wouldn't spread too far, too fast to cause gasket issues. Maybe.

 

[diesel4me]

I wouldn't be scared to heat it up good..maybe not orange,but warm enough to expand the manifold around the plug enough to let it loosen..the intake gasket wont melt that easily..
Often you'll need a cheater pipe on whatever wrench or ratchet your using to get it to come loose..pipe wrench will help if its one of those square ended pipe plugs...

Worst case scenario if it refuses to budge,and you fear busting up the intake,you could drill it out and tap the plug for a pipe barb fitting--a lot of GM's had only a 3/8" or so hole in the heater hose nipple on the intake,so I wouldn't be worried about reducing the flow,it might even help it ,by increasing the pressure and reducing the volume some..
If its a 1/2" NPT thread plug,you could drill it large enough to tap it for a 3/8" thread pipe nipple or barb fitting,you will probably need a hunk of 1/2 heater hose over that as a bushing to let the 5/8" one fit tightly,or you could use a 3/8" to 1/2" npt adapter to allow a stock GM heater fitting to fit..

 

[tjdude]

I have heat now! Thanks again for the help i feel like an idiot.

I tried it all to get that plug out. Candle wax, heat, oil nothing got the plug loose. It was a steel plug in an aluminum intake. I was pretty certain I was about to ruin the intake.
I just used a thermostat housing with a nipple. Yeah, I don't get heat until the thermostat opens. However, I have heat.

 

[diesel4me]

Hey,its better than NO heat!...since the heater is innefective until the engine warms up enough anyway,its probably preferable to have it plumbed up that way...

Aluminum intakes suck for letting steel bolts and plugs,get corroded so badly they fuse together from electrolosis..this is why I use lots of never-seize,teflon tape or paste,or even grease,on steel parts that thread into aluminum..