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Discussion Starter #1 (Edited)
99 3.4l v6 Tacoma (5vz-fe)

220,000 miles.

I'm getting no cabin heat. I checked the heater valve and the cable is fine, tested turning the switch from hot to cold and it pulled the cable + valve from one end to the other. No leaking from the valve, also.

3 years ago I swapped out the original radiator with this one:

https://frsport.com/koyorad-c1755-oem-replacement-radiator-toyota-tacoma-3-6l-v6-at-01-04

Everything was going smoothly until about a year ago when I noticed a pretty consistent drip coming off the lower radiator hose at the thermostat housing end. It also over heated once. After noticing that, I replaced the thermostat and upper/lower hoses/clamps and drained/filled/burped.

Now, about a year later, my heat isn't working. I can hear fluid rushing around the dash when driving every once in a while. I did a little research and found that it most likely means theres trapped air in the system (I know that this could also be indicative of a head gasket issue, but I doubt that's what my issue is). I have burped multiple times and I still have no heat, and still hear the rushing fluid sound. In addition to that, I have noticed coolant splatter on both ends of my upper radiator hose, as well as on the thermostat housing end of the lower radiator hose. The other day, I noticed a small drip coming from either the inlet or outlet hose(I'm not sure which is which) for the heater core (the drip is coming from the left hose in the picture). It only started dripping after I barely touched the hose on the left (pictured). In addition, my overflow tank keeps getting drained. No overheating this time, though.

It seems to me that coolant is being sucked into the cooling system, not returning to the overflow tank, causing the cooling system over-pressurize, and the excess coolant is escaping out of the hose ends. Everytime I open the radiator cap, the coolant is full, but the reservoir is empty. I was thinking that maybe my radiator cap is bad. But, why would it allow coolant to be sucked into the system, and why would it leak out of the hoses, instead of the cap if the cap were the issue? My logic might be flawed, because I'll admit I don't have a full grasp on how it all works, but thats what makes sense to me.

My first thought is that my heater core is plugged. Would that cause the system to over-pressurize? But, if it did over-pressurize, wouldn't the cap allow coolant into the overflow reservoir?

Here are some pictures:

So, from my understanding, the inlet hose should be the one connected to the heater valve, right?

If so, that means that the hose on the right, is the inlet. The hose on the left is the one thats leaking. If not enough coolant is getting through the heater core because its plugged, then why would the outlet hose be leaking?

I'll probably do a flush on the heater core with CLR. Anyone got experience doing this with the 5vz-fe? Any tips?
 

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1998 T100 SR5 2WD
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Yer best bet would be to use a cooling system pressure tester. I should've bought/rented one and used it on my 5vzfe engine but I let it go too long and ended up replacing a lot of parts that got hosed in the process. :(

These are the two threads I created when I started finding out about the issues in my cooling system. ;)
https://www.toyotanation.com/forum/60-t-100-forum/1380009-losing-coolant-over-time.html
https://www.toyotanation.com/forum/60-t-100-forum/1427210-loosing-coolant.html

The heater core is fed by the bypass tube located under the intake manifold and exits to the rear of the engine. I can't recall where the coolant returns to from the heater core. You will need to disconnect the feed and return lines to verify that coolant flows through those lines. You should be able to backflush the heater core at that time. There's a chance that yer heater core valve may be clogged up. You should be able to verify whether or not that is the case when you backflush the core. Just make sure the core is disconnected from the cooling system before attempting a backflush. If there is anything in the core, you don't want it in the engine cooling passages! ;)
 

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Discussion Starter #4
Yer best bet would be to use a cooling system pressure tester. I should've bought/rented one and used it on my 5vzfe engine but I let it go too long and ended up replacing a lot of parts that got hosed in the process. :(

These are the two threads I created when I started finding out about the issues in my cooling system. ;)
https://www.toyotanation.com/forum/60-t-100-forum/1380009-losing-coolant-over-time.html
https://www.toyotanation.com/forum/60-t-100-forum/1427210-loosing-coolant.html

The heater core is fed by the bypass tube located under the intake manifold and exits to the rear of the engine. I can't recall where the coolant returns to from the heater core. You will need to disconnect the feed and return lines to verify that coolant flows through those lines. You should be able to backflush the heater core at that time. There's a chance that yer heater core valve may be clogged up. You should be able to verify whether or not that is the case when you backflush the core. Just make sure the core is disconnected from the cooling system before attempting a backflush. If there is anything in the core, you don't want it in the engine cooling passages! ;)
Luckily I still have in my possession a loaner cooling system pressure test kit from advance auto from working on my 1gr-fe!

I was actually planning on using it on my 5vz because I had over heated one time and I just wanted to double check the head gasket situation. Already did a combustion fluid test and it came up negative, but I don't want that worry in the back of my brain.

I found yesterday that I still had a bunch of air in my system. I put the truck on ramps and connected a spill free funnel (which I should have purchased a long time ago) and burped it until i was confident all air pockets were released. My heat returned, but not to its full potential. I topped off the radiator and overflow, and cleaned up all the coolant stains. Today, I noticed the outlet heater core hose at the firewall is still leaking slowly. I REALLY don't want to have to replace the hose as they are pricey.

Ill have a look see for that bypass tube when I get a minute. Is garden hose water alright to flush the core with and do you suggest any cleaning agent like CLR? I don't want anything thats going to be corrosive and cause more issues, of course.

Thats pretty crazy that your heater valve corroded that much. I don't think mine has that issue, but i'll check it out as well.

Thanks for the information!
 

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1998 T100 SR5 2WD
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As long as you don't go crazy on the pressure, using a garden hose will be just fine. I'd suggest using a catch bucket just so you can inspect what comes out of the heater core. You never know...it could be a boat load of gold! :D
 

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Discussion Starter #6
As long as you don't go crazy on the pressure, using a garden hose will be just fine. I'd suggest using a catch bucket just so you can inspect what comes out of the heater core. You never know...it could be a boat load of gold! :D
Good point. In that case, I'll have to pull out my sluice box!
 

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Discussion Starter #7 (Edited)
Back flushed the heater core a few times with low pressure garden hose water, switching the flow direction each time. Its now sitting in 6% vinegar overnight (I could not, for the life of me, find anything higher than 6% at any store I could think of).

On about the third flush a piece of stretchy rubber came out (see picture). It is about 2 inches long when straight, and about 1/2" - 3/4" in diameter. Its pretty stretchy, like a rubber band. I'm certain its not from me pulling off the old heater hoses or rigging up my flushing system. What the heck is it? is there some kind of rubber inside the heater core that might be corroding? I guess it could really have been from anywhere in the cooling system and made its way to the heater core. Should I be concerned?

This pretty much all thats come out of the flush with using water only, that and a few tiny calcium deposits. I expect to see more tomorrow after that vinegar bath.

Shouldn't I be expecting quite a bit more gunk if my heater core really is plugged up?
 

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1998 T100 SR5 2WD
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How good was the flow/backflow? ;)

Never seen anything close that might resemble that piece. Only possible thing that I can think of would be the heater core valve mounted on the firewall. ;)

I'm not sure I would leave the vinegar in too long. It's a shot in the dark and if you thin out the heater core too much, yer gonna end up replacing it. ;)

Did you check the flow from the supply line and return line? Did you git the chance to inspect the heater core valve? ;)
 

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How good was the flow/backflow? ;)

Never seen anything close that might resemble that piece. Only possible thing that I can think of would be the heater core valve mounted on the firewall. ;)

I'm not sure I would leave the vinegar in too long. It's a shot in the dark and if you thin out the heater core too much, yer gonna end up replacing it. ;)

Did you check the flow from the supply line and return line? Did you git the chance to inspect the heater core valve? ;)
I was thinking it might be from the valve as well. Is there a little gasket inside that helps seal when the valve is turned to the off (cold) position?

I left the vinegar in the core for 12 hrs, flushed it out with water, then filled with coolant. Hopefully it holds up. I used vinegar on recommendation of another user. They used 9%, but I could only find 6%.

I spaced checking the feed line from the block to the heater valve; I just pulled the line from the inlet of the valve and left the other end attached to the block (today i'll pull the feed line off the heater valve again and apply low pressure at the radiator cap and make sure its not blocked off). The valve flowed just fine, and I replaced the outlet heater hose, and made sure there was flow from the outlet of the heater core to the block. Everything seemed to be working/flowing properly.

There was virtually no gunk that came out of the core after letting the vinegar sit overnight and flushing with water reversing the flow a few times. I'm stumped. I even connected a hose to the inlet on the block where the heater core outlet line connects to, and pulled out the thermostat and ran water to see if there was further blockage, and there was none. I did the same with the radiator, and reversed the flow there, but there was no blockage.

After I drained all the coolant (I even found the mythical passenger side engine block drain plug) I replaced the upper and lower rad hoses with OEM, as I read that they are a slightly smaller diameter, therefore tighter fit, than the aftermarket ones I had installed. Replaced the thermostat with OEM and made sure the jiggle valve was oriented in the 6 o'clock position as I did with the previous one. Another member mentioned that the OEM stat opened a little sooner than an aftermarket one did for them, so I figured I might as well.

I REALLY hope I'm not chasing a leaking head gasket. I did do a combustion fluid test before all this and it passed, but only left it on for about 3 minutes. I got a suggestion that I should leave it on for about an hour because it might take the long to detect a small combustion leak. I'll do that today, and if it passes, I'll do a pressure test overnight, then pull the spark plugs and put my bore scope inside to see if there is any coolant inside. Engine and tranny oil are clean, no milkiness.
 

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1998 T100 SR5 2WD
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I figure you could put the hose on the feed hose from the engine and put a catch bucket on the return line and see if the coolant/water will flow out when you turn the water on. That should give you a good indication if the feed line is gitting some good flow or not. ;)
 
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