I actually went further on this. The plumbing on the 4.6 with dual units has 1/2" id heater hose and piping. The feed from the back of the engine has a flow restrictor in the hose that runs to the supply "T". I had removed that to get the full 1/2" flow (replaced it with copper pipe and 2 clamps). That made it better for awhile.
Following that, I cut out both "T" connectors (supply and return) because they also have the same (1/4-3/8's) restriction. I replaced those with full-flow 1/2" ID brass "T"s and 1/2" ID brass barbed fittings. I also installed 2 shutoff ball valves; one on the supply and one on the return so that if a heater core blew, I could shut off the coolant flow through the cores, and also so that I could "add back" the restriction of that was necessary.
The heat is now sufficient to deal with 6 degree weather, *but* it is still not normal. I did replace the thermostat as well. The one that was in there was not closing fully and it was taking a long time for the engine to heat up. Now it warms right up. With such a large cooling system and radiator, you really need a thermostat that works 100%. This is the 195 degree unit.
At this point, I think my particular issue is one of flow. It's not like a chevy, where there is a plumbing takeoff right on the pump for the heater. This comes off the back of the engine (manifold?) and if it is restricted (clogged?), it doesn't seem to make any difference as far as cooling the engine, but it seems to make a big difference in heating the cabin. My next step will be to check for air and to bleed it because sometimes when I make a turn or stop fast, the heat comes blasting out of the front. That sounds like the core is good and clear, but the hot coolant isn't going through it properly.
Again, removing the restrictor and replacing the "T"s with brass plumbing, full-flow 1/2" ID "T"s and barbed fittings has made it much, much better.
One last note... The system has been flushed and I am yet... and I mean yet... to find a single piece of debris that could clog the system. Coolant is green-brown, but does not appear to have any sediment. Also remember that I have confirmed that the blend doors on both the front and rear of the Expy are working properly. It was also recommended to me to use a wet vac on the supply side of the heater cores to withdraw any sediment. In my case, that would be my last course of action because of the high heat output after certain turns and stops. A clogged core pretty much stays clogged and turning or stopping shouldn't make it work all of the sudden, unless there is magic and a gremlin involved.
I had great heat in rear but cold in front. Found that blend door problem existed. Changed out actuator and blend door. Good heat front and rear. Six months later great heat rear no heat front. Blend door functioning properly. Assumed i needed to flush system. After chemical flush, no heat front or rear. Seems luke warm at best. Heat is good for a few seconds after fan is on. Seems like fan is over cooling the cores.
Is there a sure fire way to ensure that there is no air in system? I put front up on ramps and ran with lid off of coolant reservoir. Never saw any bubbles/air come out.
Will try the shop vac trick you suggested for sediment. But it seems that there should be a way to flush the entire system, block and all, and regain the original heat even with the restricted t's in the system?
Yes, that does make sense but mine sounded just like yours without the blend door issue and now it is improved. All things being equal to new, you should have heat. This is clearly a weird problem, but one that a lot of us seem to face, especially on high-mileage vehicles.
Another update on this... Using the ball valves, I shut off the supply and return. That allowed me to isolate the heater cores from the cooling sytem (those valves are great to have). I picked up a small hand pump and pumped air into the cores and then into a pail. I then filled the cores with CLR. Then I attached the input to the pump to the core input so that I had a backflush-direction, closed loop. I circulated the CLR for about 15 mins. Then I let it sit a bit and reversed the direction. I then took water and pumped that through to flush the cores free of the CLR. I also did this in both directions. The result was that some white water (calcium/lime?) came out with rust particles. Not a tremendous amount, but it was clear to me that because of the small diameter on the factory "T" fittings, even a small (1/4") particle of rust can block the flow. Now, with the larger "T"'s, no restrictor and flushed cores, I am getting plenty of heat on the higher fan settings. I still get a bit more from the rear core, but that is because it flows through that one easier and there is no balancing valve to equalize the flow. I will probably add one and I might even flush the cores more vigorously again come summer. I used this isolation method because I didn't want to flush the entire block and radiator, and this way, I end up replacing perhaps a gallon of antifreeze, no more than that. So, the moral of the story appears to be that on older vehicles, cast iron flakes end up circulating and blocking the small orifices in the fittings and perhaps the cores if they have any sediment in them. Restoring flow so that they can pass these particles seems to do the trick. 187,000 miles and counting.
First of all, thank you got this thread. It has given me insight that I never would have thought of. I just wanted to ask a question for clarity in my own mind. I have the exact same problem you have had, 216,000 miles on the old beast. When you are referring to the "T-fitting," do you mean the factory built in t-fitting that are part of the heater core hoses?
And if so, are these what you replaced to eliminate this problem?
I have done everything this thread suggested, except replacing those fittings. I'm thinking that is the issue, I just wanted to confirm that they are the one you are talking about. Thanks again.
You're welcome. Your post comes at a great time for people with this problem because I went much further and it is fixed. To answer your question, yes. The "T" fittings are the ones that connect the rear core and front core circuits to the main circuit off of the engine. The restrictor is described by some as being put in there to reduce the surges through the cores during high revs. Once these are replaced with valves and "T's" as I have done, you can duplicate any restriction you want from full open to full closed. I just like the idea that I can isolate the cores for flushing.
But now I want to tell you and others what happened. These restrictors bring out a symptom of the problem. They are not the real problem.
As we all pretty much know now, our trucks lose the heat due to the blend door, actuator, switch or a flow related problem.
My Expy now has 204k and all the mechanicals are still ok. Our problem was definitely with flow. Once I took out the restrictors as I mentioned, that allowed flow to the core, but the core eventually clogged up.
We all lose the heat in the front core first because of the way it mounts (vertically). The small tubes run horizontally and therefore, the core clogs with debris from the bottom to the top over time. So you get less and less heat as sediment builds up in there.
The sediment mainly comes from 2 places; corrosion inside the block; small particles of rust, and small rubber particles from the inside of the hoses. These are what get in the cores over time.
Diesel folks have coolant filters. Even though mine is working 100% now, I may add one. They seem pretty good. But, getting back to the sediment and clogged cores, you can still get flow through a core and get little heat, so looks can be deceiving.
To know if your core is clogged, if you put your fan on the lowest setting with (of course) the temp control all the way to hot, and you get a little heat, but you lose it when you turn the fan up higher, then you are not flowing the proper amount of water through the core.
Chances are that it is pretty clogged. I flushed my core as I have noted before, but it was never 100% and it did eventually get bad again about a month ago. So, here is what I did.
I went to a service station and had them flush and refill the system with a machine. They also flushed the cores individually with CLR and then flushed with water. Following that, I noticed a little more heat, but after driving for a couple of weeks, I ended up with 0 heat out of either the front or back. So, here is where I got serious... BTW, my engine (4.6) never, ever overheated.
The first thing I did was to backflush the cores. I could not believe what came out of them. Dark muddy-like coolant. Surely this was dredged up from the bottom of the block and perhaps bottom of the radiator after the machine flush.
The cores because of the buildup (lime?) on the inside of the tubes, duplicates small orifices and actually filters or grabs these particles out of the cooling system.
Apparently cores become good filters, which is why they clog. So, once this was out of the cores and I had clean flow, I hooked everything back up. I had heat again... Yay.... but, sadly... only for a week. So, yes... I had a gremlin in my system and this is what I did. YMMV...
I have a Jabsco reversable oil change pump that is designed to extract and refill crankcases in boat engines via the dipstick tube. I hooked up heater hoses to it (one clear section to see the fluid) and then I flushed the core individually.
With my valves off, the new, clean coolant was isolated from this flush. The only thing I did this time that made a BIG difference is that I used Limeaway, not CLR. The Limeaway gel works great. I've used it on aluminum humidifier panels, so I know it's safe. We have to be VERY careful of the cleaners we put through our cores because they are aluminum (this is why that great Dupont 15 minute flush with the neutralizer in the top of the can is a dead product now. Great as it was, it would eat right through an aluminum core).
So anyway, I first set the core up by filling the hose to the pump with Limeaway and then I closed up the loop and sent the stuff into the core (there will be some air in the line. You can add more Limeaway if you like to fill it up, but again, there will still be some air which makes no difference).
Basically the Limeaway goes back and forth to push and pull through the core. I let it sit for about 10 minute cycles for about an hour. Each time I ran it, the view through the clear tube showed it getting darker and darker.
Then, I open the loop and using a bucket with hot water, I put the inlet hose to the pump in the bucket which then feeds to the return on the core. Then the input of the core has a hose that runs back to the bucket. I turn on the pump and voila... all the sediment starts coming out and the water in the bucket turns black with all the tiny particles of rust, etc.
Then the bucket gets dumped and then the process repeats until the flow in either direction is clean. Then (and this was the startling part), I filled the core with Limeaway again and did that part one more time.
I let the pump run and run in a closed loop and all of a sudden after about 5 minutes, a whole load of rusty particles were flowing through (I took a video of them going through the hose).
Apparently, the tubes get filled with this crap, the flow stops through those tubes, and then the ends get covered with scale buildup, sealing it in. I think the Limeaway was breaking down the scale and the flow was forcing the rust/sediment particles out.
So, I did that for a while and then did the hot-fresh water flush until it ran clean. Since I had flushed it with fresh water, I just removed the pump and its hoses and hooked the cores back up to my shutoff valves, opened them up and started the engine.
In 15 minutes, (using my infrared thermometer - an inexpensive-must-have-tool) heat coming out of the vents was 118 degrees on full fan. That increased to 130 in a few minutes. Now, bear in mind that this is heating the outside air, which was 36 degrees. So using a trick of mine, I was able to get the heat to 150 degrees.
In the winter, I remove the plug on the AC refrigerant pressure switch which is located on my 99 next to the washer fluid tank. That lets me turn on max-air without air conditioning to recirculate and reheat the heated cabin air. Believe me, the defroster works just fine without the ac to remove moisture when it's below 32 degrees. This will heat up your cabin much, much faster in winter. Then, when warmer weather comes, just open the hood and plug it back on. Easy.
So that is pretty much all I know about our systems. The blocks flake off rust and the hoses start to break down. I did replace my upper hose because it lost it's shape. If yours isn't "firm", then I'd say replace it. I did one other thing too... I removed the coolant tank and cleaned it. Using the pump, I could evacuate the coolant from the reservoir tank into a bucket and remove the tank (a good way to inspect the lower hose too). Again, Limeaway and hot water in the old kitchen sink worked wonders. Now it's nice and clean and soon things will get back to normal with my wife. She doesn't understand how useful a kitchen sink is when it comes to automotive work. ;-)
Last edited by developer; 11-30-2014 at 07:46 PM.
Reason: typos, typos, typos!
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