Coolant Flush Questions

I just replaced my radiator (due to a leak) and while I'm in there I'm trying to get the cooling system all sorted. Truck has 220k on it, radiator and block drained pretty clean so I think it's been recently flushed but I have some concerns.

I wasn't getting any heat so I pulled all the heater core hoses, they were really crudded up and heater core was clogged (red particulates and rust). I flushed it with garden hose till clear, replaced hoses still no heat. Figured it was air bubbles so I jacked the front up and burped it for a while, seems clear. Inlet hose and outlet hose are similarly hot and if I pull either hose while engine is running I definitely have flow but it's pretty low unless I rev it. Sort of like a flow the size of a pencil at idle and then flow is pretty much the whole hose when I rev to about 2k. Not sure what normal is as far as flow thru the heater core. Closed the system back up, ran on the highway for a few minutes, still no heat thru the vents, maybe a tiny bit warm but definitely not hot. I also did the throttle body a couple days ago and the coolant lines to the IAC were totally clogged up.

Clearly at one point the cooling system got really bad and then someone did a fairly half-assed flush. My concern is that there might be some coolant passages in the engine block that are still clogged up, preventing full flow to the heater core. Maybe also this could be a symptom of water pump starting to go bad? I've only ever had water pump bearings go out which doesn't really reduce coolant flow until they implode but could it be wear in the pump housing or something reducing the output? I know the timing belt was done recently I would have thought they also did WP but I don't know for sure.
Not sure what else could be causing the lack of heat, I know there's not an airlock to the heater core. I suppose it could still be flowing but not well and have some restriction still in there but I'm worried the restriction might be in the block.

Haven't had any issues whatsoever with overheating in the six months I've owned the truck.

What are thoughts on chemical flushes for these trucks? I haven't found much info searching other than people saying 'you shouldn't need the chemical unless your coolant looks really bad'. Right now I'm running on distill h20 while I keep messing with it so I'd like to get this sorted in the next day or two before I fill up with coolant again.

 

What shape is the heater valve in? Do you have good flow through the valve when its on?

 

Yes I pulled the valve and cleaned it. Been thinking on it, I think what I’ll try next is opening the drain plug on the block and hooking a garden hose up to the hose going from block to heater valve so I can back flush the block with some pressure. Right now the block is draining totally clear after a basic fill n flush so this should tell me whether I’ve got blocked passages. If not I guess it’s something to do with the flow thru the heater core?

 

Never heard of distilled water from a garden hose. Learn something new every day. Thanks

 

Oh yeah you just hook your pot still up to the garden hose. The trick is you gotta fire the still real hot with an oxy-acetalyne torch so it can keep up with the hose pressure

 

Thats really smart, guess thats why I never thought of it. Does it remove all of the impurities which clog radiators, heater cores and hoses ? I have a lot of iron in my well water Ill have to get me a pot still.

 

Ok I'm really stumped on this one. Still have no heat, like none at all. Here's what I've done: new radiator and thermo (unrelated), garden hose pressure flush of block, same for heater core. Took out that little in-line valve on the heater core inlet , cleaned and checked that it's working. Thermostat seems to be working fine, truck gets up to temp rapidly. Fan is blowing plenty of air. Hoses in and out of the heater core feel like they're at operating temp when compared to rad hose (don't have a ir thermometer here). I bled the heater core by cracking the hoses with the engine running and I am definitely getting flow. I'm not sure how much is normal, it's definitely not full flow of the hose at idle but when I rev it it flows more.

The photo is a still showing the flow at idle, the zip file is a little 5-second video. Is this my problem? Seem likely to me that the heater core is damaged or obstructed and it's reducing flow but what I don't get is it's really putting out 0 heat and it's in the 50's here so I would think even with a restricted flow I would be able to feel some degree of temp change. Also if I rev the engine I get much better flow but I'm still not getting heat even when I've been running the engine for an hour at highway speed.

The only other thing that's going on I know of is that the cold-hot dial on the dash which opens the valve on the heater core inlet is frozen up so I'm operating the valve manually from under the hood. I don't think this would make a difference though if I remember right from when I was poking around in there that dial only operates that valve.

I just don't get it. All the heater core is is a little radiator, right? So if the truck is at operating temp and there's some flow through the core and the blower fan is working why aren't I getting any heat at all?

 

Sure looks like that heater core pipe is crushed in your pic

 

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Yea it is, I've been meaning to cut it back luckily there's enough sticking out that's undamaged. But it's not as bad as it looks, maybe would restrict the flow by 15-20% but I'm sure it's not what's causing this total loss of heat.

 

I guess maybe the next step is to try flushing the heater core with a heavy-duty chemical? Should I use a regular radiator flush? I would disconnect from the rest of the system so I'm not worried about gaskets etc so maybe I could use something more aggressive. Any thoughts on CLR? Would probably set something up with a bucket and a pump to run overnight.

 

Maybe I missed what year you have but have you confirmed that your air mix servomotor is operating correctly (if yours has it)? If the dial on the dash is not turning possibly your servomotor is bad and therefore not redirecting the air to blow over/through the heater core pushing hot air out the vents. That's the way I understand how it works anyway. I didn't have heat for a couple years. Pulled and tested the servomotor per the FSM and it was bad. Replaced it and all was good through last winter.

 

This would explain my problem except that I don't think I have one on my 2000! Symptoms are pretty much identical but looking at my FSM I can't find any reference to a servomotor, I think everything is manually/mechanically operated via the dash levers. As far as I can tell they all work right except for the one which operates the blend valve on the heater core inlet which I've got disconnected so I can do it by hand.

 

I think you're correct. 2000 is not the same. Still has to be some way to redirect the airflow (surely there are people here who know) so I'd try figuring that out. Seems to me that if the dial/lever won't move to hot then that's where the trouble is.

 

Well all the ones that operate the airflow vents work as far as I can tell. I think the one which is jammed is only operating the blend valve but I could be wrong. Trying to find a diagram in the FSM but the one I have downloaded is hard to navigate it's all in folders and individual files

 

Is the heater box getting warm?

 

With both lines disconnected going into the heater core. How is the flow in and out? The fan obviously blows air from there. If it's not warm in the heater box that could be an indicator of something. If you find that the heater core is backed up, that's what I'm thinking based on what you've described thus far, you can try using an acid like vinegar to break down that crap. Or clr like you mentioned. I've used both before on a different vehicle. What really helps the acid to work for clearing blockages is heat as well. The car I was working on with these acids was a Geo Metro, so I wasn't too concerned with adverse effects from the acids.

 

CLR is good. Fill core let it work. The Longer the better. I do this for tankless water heaters which heat well water on demand. Dissolves calcium, rust and lime scale well.

 

I'm not sure that I can reach it anywhere without taking the dash about to find out. I'll poke around in there.

Yeah I think this is the next thing to try. I'm not at my shop at the moment but I'll be back there in a week I can set up a bucket of CLR with a little pump and an aquarium heater and give it 12 hours of hot chemical flush whatever comes out ought to tell me for sure whether the core is the problem, and hopefully will fix it. Will report back.

 

I would recommend staying away from the chemical flushes if possible as they are typically pretty strong and can result in leaking cooling components (heater cores for example) shortly after use.

Not just a hunch, I owned and operated a chain of auto parts stores for 16 years so have a little experience/knowledge on the subject.

 

Yeah it's a last resort for me, I'm pretty leery of anything other than oil and coolant normally. I'm going to do just the heater core so I'm not worried about the engine and I figure it doesn't work now so worst case it starts leaking and I have to replace it but I'll have to do that anyway if I can't figure this out.