Engine getting too hot, vents blowing luke warm.

I have been fighting this no heat situation for over a month now. Car is a 94' Caprice wagon. Previous owner said he just replaced thermostat. I replaced the radiator, hoses, and water pump. At some point the bleeder on the thermostat housing was swapped out for an aftermarket temperature sender. Thermostat did in fact look new, and looked like it was the right one for LT1 cooling system (though I've only ever seen them in pictures online). I flushed the heater core with garden hose. Old coolant was brown sludge. Had water flowing clean in both directions through core. Filled and bled the system best as I could given the lack of bleeder valve. Hot heat and the car wasn't overheating. I drive the car and heat fades away. I have since flushed the core 2 more times with water and air. Second time I spent a good 30 mins doing so back and forth and using air. Each time I get blazing heat until I drive the car and it fades away.

I ended up putting the brass T shutoff and clear hose on the thermostat housing so I could properly bleed air out of the system. I also put on a replacement autozone coolant reservoir cap. Bled the system again and a lot of air came out. I did not have the front end on ramps this time cause there is too much snow. Bled till no air came out. Still have crappy heat and the temp gauge goes past halfway especially when sitting at lights. Even when its 4 degrees out. If I accelerate hard from a stop the temp gauge falls to about 1/3 and I get some temporary heat from the vents. Fades away fast. Cooling fans are rigged to switches in the ash tray. Can hear them run but they don't lower engine temp.

I have to think there is still air trapped in the system. But if so why can't I get it out? Tried a couple more times to bleed and no bubble come out. I would hope its not a blown head gasket. Any ideas where to go from here? The fact that I can get heat sometimes makes me think the heater core can't be bad. I can clearly feel the radiator hose get hot when the thermostat opens so I think its ok.

I would think you have a block in the system somewhere either the heater core or the radiator but my experience with B -body's is limited i'm sure someone will chime in with more. Jeff

If your temp gauge is reading good and you feel both heater hoses and they are hot then it's a good indication it's not the thermostat or the core.

Check under the dash for any vacuum leaks in the hoses. Maybe the heat control is not opening up all the way. Also does the blower motor work on all speed setting or just on high?
If it only works on high you might have a bad blower resistor.
While your under the dash you can also pull the blower Motor [(3) 5.5mm bolts] and count the teeth on the fan. If it's 31 teeth then you have an aftermarket blower and there is little hope for heat. If it's the factory 49 tooth fan take a moment and breathe a sigh of relief!

If it was me I would drain the coolant (including removing the knock sensors to drain the block) replace all the coolant with regular water and run some Prestone FLUSH through the engine until it gets up to temp, drain it again, refill with plain water and run it again for a rinse then drain, flush the core back and forth with a garden hose until clear and then refill the system with green coolant/water mix.
That should remove any and ALL traces of sludge.

Blower works fine and the blend door has full range of motion. When the heat is working it's HOT! When I replaced cooling parts I drained everything except the block. When I pulled the knock sensor the old coolant was frozen. There was nothing I could so I just refilled the system with fresh coolant. There is a hint of brown to the new coolant and I plan to flush the system again this spring.

Another thing I tried was to pinch the heater hose a few seconds to build a little pressure then release to force air or blockage through the core. After doing this a couple times the return hose got really hot just like the feed hose. Heat worked for a min or two then faded away.

I think tomorrow I will try to jack the front up high and bleed again.

Is the flow restrictor still in place on the heater hose?
Did you pull the carpet up to see if you have a leaky heater core?
You said you replaced heater hoses just curious if the restrictor was still in place.
It's job is to keep the pressure from putting a hole in the heater core. Maybe you got a leaK going on and it's running under the rubber backed factory carpet. (I've had it happen)

I know the previous owner supposedly put a thermostat in it, but unless you have receipts, put a GM thermostat in it. I went through three aftermarket thermostats before I finally gave up and got a GM one and the car worked fine ever since.

Are you sure the water pump is working correctly? Are the two metal heater hose pipes free flowing? Does the steam line flow freely? Can you push water into it and have coolant come out the front pipes on the motor?

I know you listed all the mods to this car in another thread, but I would get the cooling fans working from the computer as soon as possible. I've seen way too many bad things happen with cooling fans wired to switches, because the driver inevitably forgets to turn them on, and all it takes is one time.

From personal experience, the restrictor does nothing,. of course te guru's and naysayers will diagree,. i live in the frozen north, and have driven B-body LT1's all winter with and without restrictor,.it,s supposedly in there to stop too much pressure going thru the heater core at high rpm,.. then the heater core plugs up with debris,.go figure,.

I,m with Joel on this one,. the engine is circulating the water too quickly at rpm,.

This whole thing about bleeding too is puzzling to me,. i fill the rad,. leave the bleeder open, squeeze the bottom rad hose hard a few times and the top one till i get coolant out of the bleeder,. then i start it and let it idle till its warm, heater on high heat defrost,. then open the bleeder a little,. if i get coolant,. i call it quits,.
I,m always amazed of stories of wheels up on blocks etc,. if the water pump doesn't have enough flow/pressure to push the air around till it comes out,.
then the water pump is NFG,..

JMHO,..
I,m amazed by stories of

I did the throttle body bypass today because I keep finding coolant IN the throttle body. I also unhooked the heater core and took out the restrictor to inspect it. Looking through it I thought it looked like just molded plastic with a smaller hole in the middle. Figured I would drill the hole out a little larger. Turns out the smaller hole is actually a rubber grommet type piece with a metal spring. I destroyed it with the drill bit so I pulled it all out. I blew air through the core. I then pressurized the coolant bottle to force coolant back through the core till it flowed out the heater hose. Put everything back together and I have heat. Not sure for how long though.

If the heat is hot and then dies quickly, either the thermostat is acting funny or the heater core is clogging quickly. Based on the condition of the coolant, it could be both.

The lower "supply" hose to the core always gets hot. The upper "return" hose gets hot when the heat works. Would make sense to say heater core is plugged or has air trapped in it. What doesn't make sense is when I flush it, it works great temporarily then fades away. Even after multiple flushes. And the fact that it works under hard acceleration and engine gets cooler. That makes me think air in system or weak water pump even though it's new.

Perhaps the new water pump is defective. Maybe casting flash inside hindering flow or an impeller issue? Is it an OE pump or aftermarket?

Every time you flush the heater core, are you getting junk out of it? If so, then the heater core will continue to act as the filter for the system until the crap stops breaking loose.

There isn't really a noticeable amount of crap coming out when I flush. I agree with what your saying though.

I drove it to work today and the heat was blowing hot and the engine temp didn't go past half on the gauge. I did notice when I accelerate hard the temp gauge drops and the air blowing out the vents become flesh-melting hot. It has to be a crappy replacement water pump or bad thermostat.

On a side note, the car is becoming harder to start. Used to fire right up, and now it takes a lot of cranking. I really hope this car isn't becoming a money pit.

After driving it the past couple days my heat has been hot and the engine not overly hot. I suspect it is a bad replacement water pump (is new not reman) or a bad thermostat. As I said before with higher rpm I get better heat from vents and the engine temp drops. So water is definitely not circulating well enough at low rpm. I am leaning towards water pump more so than thermostat.

If I were you, I would use something like this before your heater core: http://www.ebay.com/itm/Heater-Hose-Filter-That-Stops-Radiator-Blockages-Clear-To-View-Coolant-/400781344426?pt=AU_Car_Parts_Accessories&hash=item5d506dfeaa&vxp=mtr

I agree, a circulation problem. At higher rpm, (as i understood, only DIY switch electric fans) your engine makes a lot of heat, but cooling lacks (no fan running, no electric fan turned on, temp gauge is low, lots of heat) As soon as your rpm goes to cruise, engine makes less heat and the cooling is sufficient. (= less heat through vents)
IMO, thermostat.
I agree with Nick on the part of bleeding the coolant. It's no rocket science and air will go out eventually.
Best of luck with chasing your problem.
Pete

8 months later,..

Wow. Missed the post date lol.

wow, indeed.....