Heater core no coolant circulation, but not plugged

Hi guys, I've been trying to track down an overheat problem(temp sender def. faulty, but van does ACTUALLY overheat sometimes as well...water boiled out of overflow tank once). In part, I've noticed that my heater core doesn't blow hot...so I installed a flush T and flushed the cooling system, with flush additive...everything came out surprisingly clean(there is receipt evidence that the previous owner had a shop flush the van as well). Hoses going in and out of heater core didn't get hot, so I bypassed the core open/closed valve so that the core is always open. Still, the hoses don't get hot...so I've drained coolant, disconnected one heater core hose at the installed T, and blown into both ends(so in one case, I am blowing into the left side inlet of the engine, and I hear bubbles coming out top of engine where coolant cap is off. In the other case, I am blowing through the heater core and into the right hand side outlet of the engine, and I also hear bubbles coming out of the fill cap. In both cases, there was minimal restriction to blowing, just fluid backpressure).


So the heater core and lines aren't clogged/restricted, and the water pump is pumping some water(I replaced the lower radiator hose with a piece of clear vinyl hose temporarily, to watch fluid flow...when I rev engine, the fluid vortex's and small bubble fly through!). So why isn't fluid circulating through the heater core? Is this some kind of 3Y configuration issue, or is my water pump weaker than it should be, or is there some other explanation?

Any thoughts appreciated. Big thanks to all the contributors on this forum, this site is an incredible reference source.

Cheers,

Alex

Anything is possible, but water pumps usually fail when bearing failure leads to seal failure which results in a leak. The business end of the water pump is a simple impeller that spins, so about the only thing that could happen would be disintegration of the impeller due to rust or perhaps it getting loose and spinning on the shaft (I've never seen either). To determine overheating you will need a working temperature gauge or have a way to measure temperature. Engine coolant can also be forced out if combustion gasses are entering cooling system (resembles a boil-over). If you think this may be happening I'd use a sniffer to check for combustion gasses here. Overheating issues with these vans can be caused by aftermarket thermostats. There are several that will fit, but do not work well. I've experienced this 1st hand and as a result will now only use the OEM t-stats that are listed by application for the van.

FYI, The heater system on the van bypasses the thermostat. The heater hose circuit gets full flow regardless of t-stat position. If your coolant is hot and there's no restriction in the heater system, then your heater hoses must get hot. I guess it's possible you have an air bubble in the system causing cavitation, but those will typically only interfere temporarily and clear themselves after a single heat/cool cycle. If you've ruled that out, verified there's no combustion gasses in the cooling system, and verified t-stat is good (and OEM) then the next logical step is to pull the pump. Tim

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Originally Posted by timsrv

Anything is possible, but water pumps usually fail when bearing failure leads to seal failure which results in a leak. The business end of the water pump is a simple impeller that spins, so about the only thing that could happen would be disintegration of the impeller due to rust or perhaps it getting loose and spinning on the shaft (I've never seen either). To determine overheating you will need a working temperature gauge or have a way to measure temperature. Engine coolant can also be forced out if combustion gasses are entering cooling system (resembles a boil-over). If you think this may be happening I'd use a sniffer to check for combustion gasses here. Overheating issues with these vans can be caused by aftermarket thermostats. There are several that will fit, but do not work well. I've experienced this 1st hand and as a result will now only use the OEM t-stats that are listed by application for the van.

FYI, The heater system on the van bypasses the thermostat. The heater hose circuit gets full flow regardless of t-stat position. If your coolant is hot and there's no restriction in the heater system, then your heater hoses must get hot. I guess it's possible you have an air bubble in the system causing cavitation, but those will typically only interfere temporarily and clear themselves after a single heat/cool cycle. If you've ruled that out, verified there's no combustion gasses in the cooling system, and verified t-stat is good (and OEM) then the next logical step is to pull the pump. Tim

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It has been my experience with radiators and heater cores to find a surprising amount of sediment and general debris internally. This after flushing water comes clear, and the offending rad is removed and flushed with a garden hose in the driveway. I wonder if a partial blockage, not displaced by in vehicle flushing, is causing the normal coolant flow to divert from the core, with the heat control valve open. This build up internally could also cause a lack of heat transfer from coolant to rad or core?? I respect Tim's experience explicitly, but I have had good results using after market thermostats in both of my vans, and other older vehicles as well. I have been running a 180 deg thermostat in my 85 for 15 years with no ill effects.If I drive it in winter, I would up it to 200, as I can tell the difference in heater output.

When I couldn't get cabin heat it was because my heater core was partially clogged. I took off both hoses going to the core and flushed one way, then the other(backwards)-that way you are isolating the core and not flushing crap into the rest of the cooling system. A lot of nasty came out:clap: and I was given heat!

Thanks for the tips everyone. I am running with a drilled/clipped out thermostat right now(just the metal ring and rubber gasket), haven't experienced overheating since doing that, but haven't gone for anything other than a town drive either. I just picked up a freebie lifetime warrentee replacement alternator yesterday(I *may* have gotten coolant on the old alternator when pulling thermo), and asked about water pumps...only $45, so I bought it(the vanes are metal) and will likely replace water pump and heater/radiator hoses, and just bypass the rear core for now(the fan for it doesn't work, I don't like the long run of hose from it to the driver side, want to isolate issues and airbubble pocket potentials). Pulled the radiator out yesterday and did some additional vinegar/low pressure flushing(in apartment bathtub, working on car in a public parking lot without garden hose access, but will access a hose at some point to isolate and flush heater cores again), and more crap did come out(some little bits of deteriorated rubber even), but I don't think it was enough to cause overheat.

I'll read up on water pump swap and hopefully get everything put back together today, maybe get a new temp. sender on order too.

I'm surprised at the use of the corregated radiator hoses, that have and exposed wire coiled up the inside(to prevent implosion from vacuum I'm guessing?)... on my old hose, the wire was badly corroded and potentially chunks had broken off and entered the cooling system. Also, the large nipple where the lower radiator hose attaches to the radiator is badly corroded(all the way through near the edge), and I think this is because it was in contact with the wire.

Since I have the radiator out, I might just stop by a shop with it and see if they can pressure test it for leaks...any thoughts on what this usually costs, and what repair for small leaks would cost?

The link below by llamavan was very helpful when I was learning about the coolant hoses and paths of my van. There are lots of hoses! :dizzy:

http://www.toyotavantech.com/forum/c...your-Vanwagon!

Wondering if the rear heater has anything to do with it. Does it work?

Brent

Alright so everything is back together and running ok(haven't been on the highway or sitting in traffic), but I do need to get a reliable temperature sensor in there. Turns out the back heater fan does work I just had to push an extra button lol. It is bypassed now, but front heater is blowing hot, woot! I'll probably link the back heater in again when I want to replace a bunch of hoses next. Also thinking I should replace the fan clutch, just in case that contributes to poor cooling(fan clutch looks pretty ghetto with that thermister coil exposed).

Worst part of the water pump replacement was scraping off the old gasket. Old pump looked fine, probably no issue with it, will keep it as spare. Area near pump vanes, but on the engine block, was heavily pitted(corrosion?)...may also limit pump function a bit. Even with rear heater bypassed, hoses of death get water going through them.

I've tried to attach a picture of the pitting described above..not expecting the picture to upload

Brent, I did study llamavan's tutorial, and other forum cooling topics, before pulling hoses on my own vehicle...awesome reference and active help here. I cruised through Centralia(cute town) and did an oil change in the Oreilly parking lot the other day in my more functional 1986 automatic TV, on a Seattle-Coos Bay round trip. PNW is rad. I see TV's on street here all the time, enjoying active, healthy lives :lol:

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Originally Posted by aelxon

Alright so everything is back together and running ok(haven't been on the highway or sitting in traffic), but I do need to get a reliable temperature sensor in there. Turns out the back heater fan does work I just had to push an extra button lol. It is bypassed now, but front heater is blowing hot, woot! I'll probably link the back heater in again when I want to replace a bunch of hoses next. Also thinking I should replace the fan clutch, just in case that contributes to poor cooling(fan clutch looks pretty ghetto with that thermister coil exposed).

Worst part of the water pump replacement was scraping off the old gasket. Old pump looked fine, probably no issue with it, will keep it as spare. Area near pump vanes, but on the engine block, was heavily pitted(corrosion?)...may also limit pump function a bit. Even with rear heater bypassed, hoses of death get water going through them.

I've tried to attach a picture of the pitting described above..not expecting the picture to upload

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That looks like centrifugal pump cavitation damage. It appears to be suction cavitation, as most of the pitting is in the volute, near the eye of the impeller. Usually there is also damage to the impeller itself, but not always.

You may have, or had a restriction in the suction side of your cooling system. Caviation damage and corrosion have synergistic effects over time. This accelerates the pitting and wear, and reduces the efficiency of the pump, which causes a loss in flow and pressure.

I think there was a significant restriction in the heater core intake side(when I blew through both sides of the heater core, the rear heater core was still connected(I think), and pressure could have rerouted from the engine intake side and around through the rear heater core and back up the passenger pump-output side of the engine to bubble out the top). So if the engine was actually running, and the pump couldn't pump through the heater core line(on the driver side), and the thermostat was stuck shut, I guess that could create the conditions you describe.

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Originally Posted by aelxon

Brent, I did study llamavan's tutorial, and other forum cooling topics, before pulling hoses on my own vehicle...awesome reference and active help here. I cruised through Centralia(cute town) and did an oil change in the Oreilly parking lot the other day in my more functional 1986 automatic TV, on a Seattle-Coos Bay round trip. PNW is rad. I see TV's on street here all the time, enjoying active, healthy lives :lol:

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Me too! I enjoy the PNW. There's a white TV around Centralia that I see now and then...they are around and I see them quite often here in the PNW also. Funny...I work north of Centralia and on the way to work, I saw a white toyota van pulled over by WA state patrol. Couldn't have been going THAT fast. lol :LOL2:

I am experiencing poor heating.

I have removed the adjustable flow valve in line with the hose.

I have flushed my fan at least twice and cleaned the cooling system with vinager in the last 7 years that i have owned the van.

Any leads on a new Heater core?

Without getting into the back story, I'm wondering if anyone has tried changing the water pump pulley size to increase flow in the cooling system. I realize that this could be taken too far, causing insufficient heat transfer.

That's an engineering question. These type things were worked out early in the engine design stage and were set for maximum efficiency. Anything is possible, but I don't think it's likely that type mod would improve anything. The big problem with the van is the way everthing was crammed into a tight & poorly ventilated engine compartment. The radiator location and lack of cool air to transfer heat is the real enemy. IMHO, concentrating on things that improve cool air flow to the radiator would be more beneficial. Tim

I am having the same issue. Van runs fine for awhile then the heater in the front stops blowing hot and the van overheats. I have replaced the water pump, new belt with correct tension, replaced and later removed the thermostat. Disconnected rear heating route, checked the flow valve in the heater hoses, flushed the engine and hoses and heater core, replaced the radiator, replaced the fan clutch, and added a 2nd aftermarket fan. I removed the air conditioning fan and condenser to allow more air flow to the engine. I dont see any external leaks. I ordered a block leak tester to check the head gasket but i dont see oil in the water or any white smoke. Im running out of ideas of what it could possibly be. Any ideas or suggestions?

Think it could be air in the system causing the issue?

I think you are getting steam in the system. The radiator cap keeps the system under pressure which raises the temperature at which the coolant boils.

I didn't see a Radiator cap replacement listed. If you have a good parts guy they can get you a 19 lb cap.
I have one but there are no part numbers on it.

Could be air. I fill up the coolant system. turn the heater on. Let it warm up. Cool down. AND then TOP OFF the system.

Did you clean he cooling system with vinegar or CLR before the flush???

Also check your coolant for micro bubbles or a foggy appearance. (head gasket).

The coolant does look foggy...there are also little white deposits. What would that be though? I do have a new cap and flushed with vinegar awhile ago.tried to upload a picture but couldnt. If its the head gasket, doesnt it overheat because of lack of coolant (from an internal leak)? My coolant was nearly full. Topped it off and gonna test drive.Attachment 3848

Something like this threw me for a loop all summer 2 years ago.

I live in Nevada. Its 50deg in the morning and 100* in the afternoon.

I would not over heat on the way to work. It would overheat on the way home.
Then it started to over heat twice on the way home.
I could idle to bring the temp down.
Then It would overheat 3 times on the way home.

It turns out that the combustion gasses were getting pumped into the cooling system. Adding small bubbles and pressure to the cooling system until it could not pump / circulate properly. As the Head gasket proceeded to fail / leak it overheated with shorter engine running time. Until finally it ran hot on the way to work.

I changed everything as you did. New radiator, New Hi pressure cap, Higher flow electric fans, Added an Oil Cooler. Flushed the system ect.
I even changed my Head studs.

Finally I admitted that I did not put in a toyota head gasket a few years back and changed the HG.

A Combustion gas testing kit will tell you if there is gas in your coolant. ($50)
I would use it in the running hot state.

Im pretty sure its going to be a head gasket replacement. Any one have suggestions on a manufacturer? Oem is ridiculously more expensive. I can get a felpro gasket set for about $50 but the oem gasket by itself is about that much. Has anyone tried a temporary fix, like the gasket seal tablets?

Well, look at it this way ... what's the cost of aftermarket headgasket PLUS OEM headgasket PLUS doing the job twice?

Just go OEM. It will save you waaaaay more money than you're fussing over right now.

Gwen

My felpro failed after 2 years.

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Originally Posted by llamavan

Well, look at it this way ... what's the cost of aftermarket headgasket PLUS OEM headgasket PLUS doing the job twice?

Just go OEM. It will save you waaaaay more money than you're fussing over right now.

Gwen

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:wss:

Update: it wasnt the head gasket. I tested it and no products of combustion in my coolant. I borrowed a pressure tester and found a pin hole in the hose from the heater core. As the engine heated it moved coolant into the resevoir, as it cooled it drew air in from the hole instead of coolant from the resevoir. Air pockets gathered in the core and didnt allow proper circulation. Problem solved....i hope. The head gaskets must be tough to not habe failed under these conditions.

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Originally Posted by Filippo

I am having the same issue. Van runs fine for awhile then the heater in the front stops blowing hot and the van overheats. I have replaced the water pump, new belt with correct tension, replaced and later removed the thermostat. Disconnected rear heating route, checked the flow valve in the heater hoses, flushed the engine and hoses and heater core, replaced the radiator, replaced the fan clutch, and added a 2nd aftermarket fan. I removed the air conditioning fan and condenser to allow more air flow to the engine. I dont see any external leaks. I ordered a block leak tester to check the head gasket but i dont see oil in the water or any white smoke. Im running out of ideas of what it could possibly be. Any ideas or suggestions?

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Okay now, 2 things.
How does the radiator look on the outside front? If the face is blocked by those fluffy balls from cottonwood trees you'ld never see it, happened to me so I blew high pressure air through to clear it. Simple stuff but ya have to look.
But if there's a clue after it's after "awhile", Meaning obvious it's blowing or leaking or burning out the coolant lowering the fluid level to the point the heater core goes dry, thus no heat inside and then the engine gets hot.
:thmbup:
I just want to see someone pull the heater core. I had a mouse plug the plenum up with carpet fiber and I'll be danged if I can figure out how to get it cleared without pulling the entire dash apart again.

Even though i had no signs of head gasket leakage, i finally went ahead and changed it out. That was the problem. Hot gases from combustion were crossing into the coolant, super heating and pressurizing it. It forced the coolant into the reservoir and eventually the level would drop low enough to not have an adequate amount to reach the heater core

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Originally Posted by NWVanner

Wondering if the rear heater has anything to do with it. Does it work?

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I recently replaced the thermostat and flushed the system but still didn't have good rear heat.
Tapping on the metal line around the flow switch, 1 sprung a leak.
I had to cut the rotted corner off. There was a lot of debris trapped in that low corner that wasn't touched in the flush. I re flushed from the back and fixed the tube.
Good heat in the rear and stays 181* all day.



If there was any oil in that frothy green coolant, it would be an obvious head gasket. The color is indicative of an issue.

I use the Toyota red coolant in all my Toyotas.
Ill never felpro HG again! Anywhere else I would.

Hey guys<br><br>just left the house 1 mile drive and my temp gauge is almost at the ceiling! I turn the air to maximum heat and it was coming into the cab cool.. which I've never experienced. Is this a thermostat symptom?<br><br>thanks for any advice

i was 24oz low on cooolant. Things seem to be good now :) anyone know how to delete this post?

First thing I'd check once everything's not hot is your coolant level, not just in the overflow tank but under the actual pressure cap. A lot of times, this symptom is indicative of air or exhaust gas circulating instead of coolant.

Once you ensure it's all the way filled up, you can more easily determine if it's a leaky hose (see: hose of death threads) a radiator leak, or exhaust gas seeping into the system from a gasket break and expelling the coolant (that would be apparent if there's bubbles in your overflow tank after running)

Note: I realize this sounds like potential doomsaying, but I will say the first time this happened to me it was a bad radiator cap, so it can just as easily be something simple!

If the rear heater core is clogged, could that affect heat in the front? I removed the controls for the back and I've flushed the front heater core and I still get pretty weak heat. I know they are weak in general but mine seems especially weak. It's warm but if I was in snowy conditions, I'm not sure it would defrost in an hour.

Rear being clogged wouldn't effect the front unless the clog was in the common return line (unlikely). If your heater is not blowing hot, the 1st thing to check is the coolant temperature. It should be ~180° F or so. If the coolant isn't getting hot then the heater won't get hot either. If that's the case then replace the engine T-stat. If the coolant is hot, then get under the front of the van to make sure the cable controlled heater hose valve is open. If it is, then check the duct doors to make sure they're opening/closing correctly. If all that checks out then the next most likely issue is a clogged heater core. Tim