Rear auxiliary heat blows hot; dash vents only just warm (1 Viewer)

eikelben

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The temperature has been dropping around here and it's my first winter with the Land Cruiser. I had always enjoyed the blazing heat that my 2003 Tacoma produced and from what I've read, the FZJ80s produce the same sort of temps when functioning correctly. Mine, however, does not.

I adjusted the temperature mixing valve to make sure it is achieving a full-open position, which it was not previously. The valve is newer, PO had it installed – when inspecting it today, it appeared to be in great shape. Cooling system seems to be in good working order as well. PO had a new radiator installed and on 1/22/2018 had a new thermostat installed along with new coolant (as part of an engine rebuild). I'm unsure if anything has been done to the cooling system since.

Below are the temps I'm getting at the vents:
Center Dash VentDriver / Passenger FootwellRear Auxiliary
84°105°120°

If I understand correctly, the rear vent has its own heater core, which would lead me to believe it is performing as expected. Am I fair to assume that the main heater core is either failing and/or blocked? I see that back flushing the core is widely documented here on the forums, so I'm mostly seeking advice as to whether this is my next step. This post seemed to be a similar issue but the suggestion was a new thermostat and coolant. As is often the case, the OP didn't respond back regarding the outcome. Any comments would be appreciated.

One additional comment – is it typical for the dash vents to blow more forcefully for a given fan speed when the temp is set full cold versus full hot? I've noticed this to be the case. Possibly another data point?
 
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When you set to 'cold' it might turn on the 'recycle' switch so you will be recycling the air and that is always more forceful. As far as your temps are concerned you are definitely very low. I measured my center vent and was getting 165!! So yes, 80s have excellent heat. Now for your problem with no heat...can you check by hand the hose right after the heater control valve with your hand or better yet with a laser thermometer? That might be your first step.
 

ppc

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The front core could have a partial restriction or the blend doors within the heater assembly not functioning or have restricted movement. Backflush the core would be the first step in diagnosing the problem.
 
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Hi, As with all older trucks these cooling systems need proper regular flushing. Usually takes me days to flush a system out that is very dirty. Flush out the front coil or the whole system using Prestone or similar flushing fluid,follow their directions.Flush until clear water comes out. This may take awhile. If still no heat check for leaks in the system. Mike
 

eikelben

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When you set to 'cold' it might turn on the 'recycle' switch so you will be recycling the air and that is always more forceful.
Confirmed that this isn't the case.
can you check by hand the hose right after the heater control valve with your hand or better yet with a laser thermometer? That might be your first step.
The next time I get the truck warmed up I'll double check the hose. (I don't drive too often around town, mostly bike).
 

eikelben

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Flush out the front coil or the whole system using Prestone or similar flushing fluid,follow their directions.Flush until clear water comes out.
Hi Mike. Sounds like a flush is indeed the way to go. One point of hesitation has been the extremely hard water we have here – I don't really see any way around this? Do you see that as a problem as long as I drain and refill adequately? I don't know, but can't imagine repair shops are flushing with distilled water… could be mistaken though.
 
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Hi Mike. Sounds like a flush is indeed the way to go. One point of hesitation has been the extremely hard water we have here – I don't really see any way around this? Do you see that as a problem as long as I drain and refill adequately? I don't know, but can't imagine repair shops are flushing with distilled water… could be mistaken though.
When you are flushing it won't matter what water you are using...just attach the hose and let it go. When it's time to fill either get the 50/50 blend or mix with distilled water. Some will even run it will distilled water only after the flush and then drain and then fill with coolant.
 

eikelben

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I finally had an opportunity to flush the system a few weeks back. Got out some crud, but not as much as I would have liked (as that would likely resulted in larger temperature gains). Antifreeze was relatively new and looked as such. I ended up getting readings ~10° warmer than I had, so still insufficient. Rear heater continues to blow hotter than the front. Any additional recommendations? @thatcabledude – you mentioned the blower door not moving. When I switch between floor and vent settings I get the anticipated outcome. On floor some air continues to flow out of the door vents (albeit barely any) with nothing coming out of the center vents and on the vent setting, no air flows from the floor vents. All of the output seems to be low in temperature and low in fan output, at least compared to my 2003 Tacoma. That would burn your hands and could only be on high fan and high heat for a few minutes in the dead of Michigan winter otherwise you'd be roasting. Fortunately Idaho winters aren't nearly as brutal.
 

masong

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I didn’t see what year your truck is, but the “blend door” is often attached to the temperature control lever, and as you slide the lever from hot to cold it blends in outside air, the rear heater is excluded from this and draws air from the passengers butt. You may have a “blend door” that has gotten out of adjustment/sync with the heater valve setting. It may also be caused by a heater control valve that has slipped adjustment.
 
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My blend door lever got tangled in my RCA cables from my aftermarket radio. I rerouted them and zipped tied them down.
 
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Awesome I'll take a look at those two spots. I have a 97 LX450, wondering if I should go ahead and unplug the automatic ac control unit above the driver side footwell?
 
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So that's definitely not the answer, I figured pulling it off to see would be worth it more so to see if there were any water intrusions that other members had experienced. The hvac controller looked totally fine, and controls more than one would assume at first glance. Blend door and heater control valve both seem to be working just fine. I'm not totally sure how to check if the blend door is out of adjustment but it seems to move in the whole range of motion. Next up, a flush to see if the system is jammed up.

I'm also on the train of thought where I do think it's possible that there could also be air in the system or a somewhere along the coolant line that sucks in some air while the engine is cooling, which could leave a pocket at the highest point (which seems to be the heater). I'm going to park driver side high on an incline after a drive this afternoon to see if I can in theory get any air to pocket in the upper corner of the radiator.

A couple things I did notice was it seems like the white tube that feeds to the temperature sensor attached to the unit had popped off but that shouldn't be causing all the issues as it's still in contact with the ambient air. I did switch the ac unit to manual, with no changes, so I put it back into auto mode for now. It's easy enough to change it back and forth for debugging.
 
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Quick note/update, seems like I may have a heater core issue amongst all the problems. I noted above, but when I pump the exit coolant hose and the entrance coolant hose to the heater core by hand (just squeezing the hose) I noticed there was some residual or mild heating coming from the front heater.
 

masong

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To clarify, your gauge on the dash is reading in the Normal zone yes? As in the engine is indeed running at normal operating temperatures? I've cleaned out many heater cores in my life but I have not ever seen one that had a full blockage that would restrict flow that much( such that squeezing the hose would force enough water past the blockage to discern a rise in temperature at the vent). But, perhaps. I could see if a PO had used something like "Radiator Stop Leak" or some other bandaid additive to the coolant, you may wind up with a nearly completely block core, but I would also expect that to have affected the rear one as well.

I'm sure you have looked, but I would double and triple check that you don't have a heater hose that is bent/kinked/pinched or otherwise restricting full flow to the cores, there are a few of the molded hoses in these trucks that are being discontinued and oftentimes a straight section of heater hose is put in place, but the lack of molding can cause this hose to collapse, and even a little collapse can cause a pretty big restriction in flow. The rear core uses cab sourced air, so it likely is going to be warmer than the main core, which is warming external air unless on recirculate so I would expect a temp disctrepancy between them, especially if not getting full flow. I'm not certain but I would expect IF the rear heater was getting proper 195 degree water, assuming your engine is actually warning up to proper operating temp (your engine thermostat is somewhere between 180-195 degrees F) the air temp measured at the rear heater should probably be closer to 150-170deg F.
 
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Thanks for the response and feedback. I really hope the previous owner didn't use a radiator stop leak... that would be a bummer. I do agree with your train of thought and experience thus far and will take a look. Engine temp is reading 174 via my data feed, which seems close to your range but I'm not too familiar with how strict that range truly is.

Also, I need to get an ir temp reader just to have for debugging purposes.

I did notice today when doing the valve cover gasket on the 94 that the heat control valve cable seems to protrude quite a bit more than on the 1997 lx450 so I'm going to take another look at that. I thought I'd beat that one over the head but it'll be on the list. I'll also check the hoses for any potential kinks.
 
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