Issue with no front heat in cold temps

[MTL_4runner]

I am still troubleshooting this issue, but here's some background....

Since the issue started I have flushed the system throughly at least 3 times (filling with Dex-cool twice and finally with Toyota pink, although Toyota red would work fine as well). Each time I flushed, I made sure to unhook both the radiator and heater hoses (and on the last time I removed and replaced the thermostat while flushing.....so I backflushed where the themostat was too). Flushing was simple, just took a garden hose with a nozzle and sprayed into each coolant opening, hose etc and flushed until I saw nothing but clear (and did it several times). I also inspected the inside of the radiator using a flexible light (like this (http://www.prylbanken.se/images/Prylbanken.se-img_Snoskoterdelar_och_Tillbehor-BEND_A_LIGHT-Saljes_Pris_400_kr_1558.jpg)) and a dental mirror and there didn't appear to be any deposits at all (so I am glad I didn't pay for a radiator recore). I also inspected the heater core in a similar manner as best I could although it was very difficult to see much of anything because the tube openings are so small. So I put all the hoses back on, I replaced the thermostat with a new OEM one, refilled with coolant and started the truck and took it for a spin. The heat was definately better but is seemed that it got even better over time. It now heats quite well again (enough so we need to turn it down anyway) so I feel pretty confident the issue is now over.

At my next timing belt change I will change my water pump too so I will post pics if there are any anomallys found there too.

[MTL_4runner]

Well, I hate to resurrect this old thread but the heat in this truck is still totally unacceptable when the temps are really cold outside. Now I am positive this is not a thermostat issue because I've replaced it twice already and the truck gets up to temp right where it should. I also have very good rear heat but the heat up front is still very poor. So I am going to figure out the issue come hell or high water because up here a vehicle that doesn't heat well is just about worthless for 1/2 the year.

The radiator doesn't seem plugged and appears to flow properly (checked visually and with a garden hose). I haven't checked the water pump but I am beginning to suspect the heater core itself. Now today I spent a few more hours just taking apart the dash to see if a linkage slipped off, climate control doors were working and everything seemed to be working fine. So I then looked at why I had the strange situation of heat in the rear, but no heat in the front. So now I need some help again from someone in a cold climate to check the inlet and outlet on both the rear heater and main heater core. When I was outside today with the engine warmed up and the front/rear heaters on full blast in the truck (ie the heater coolant valve was full open), I just felt the inlets vs outlets with my hand. Now curiously the inlet and outlet on the rear heater were pretty close and both were quite hot to the touch (the return was just a bit cooler than the inlet). The inlet for the main heater core was very hot too (almost enough to burn me if I held my hand on it), but the outlet was fairly cool to the touch (ie warm, but definately not nearly as hot as the rear heater outlet). So could someone with a 3rd gen (perferably a 96-97, but any year would be helpful) in a reasonably cold part of the country check the temps on theirs for me?

Pic of what I need help with:
http://img.photobucket.com/albums/v648/mtl_4runner/4runner/4runnercoolanthoses.jpg

http://img.photobucket.com/albums/v648/mtl_4runner/4runner/4runnercoolanthoses2.jpg

[MTL_4runner]

I did a bit more reading in the manual last night and it said that both the inlet and outlet should be hot to the touch (which makes sense.....unlike the main lower radiator hose up front which is usually cool when the weather's cold outside) so there's definately an issue. The problem is that I'm not sure if the blockage is in the actual heater core itself or in the return line going to the motor. I suspect the heater core still because like I mentioned, the return line for the rear heater was hot and if there was no flow on the return line to the engine, then I should have little or no heat both front and back. I don't know why I didn't catch this sooner but I asked the parts guy at the dealer how often these get plugged and he said not very often so I may be that rare case indeed. I am going to buy a new heater core, install it inline with the coolant hoses and run the engine up to temp and see how hot it gets (including how hot the inlet and outlet are). This way I won't waste a full day installing a part if the old one is actually good (and hopefully I can return the heater core at the dealer if I don't need it). If the old one is clearly bad, I'll install the new one and take lots of pics of the process so others have something to go by if they run into the same issue (I'll also cut open the old one to see what the issue actually was). It's definately not something I'm looking forward to that's for sure! :bang:

Can someone still verify how hot the return line on their main heater core (per above pics) gets vs the inlet, I'd be most appreciative for the info!?

[MTL_4runner]

I have tried garden hose forward/back flushing the core before and really didn't get much of anything out so either the return hose is plugged or the heater core is terminally blocked. I am hoping I can get a cheapo heater core to try and see if it does get hot. If so, the heater core is definately the cause. I wish I had a lighted borescope with a camera so I could see what the inside looks like before I even bother (same with the engine block, heater hoses, radiator, etc), but that's pretty $$$$ equipment no doubt.

Still looking to verify how hot the return line on their main heater core, anyone?

[MTL_4runner]

I did a little research on heater cores and possible issues why there would be little or no heat and I can across this which pretty much points directly at a blocked heater core as being the most likely cause. Man, I wish I had a borescope so I could just take a peek in there and see right away if that was really the issue or not.

Article
When no or low heater output is not due to a blower problem (plenty of air coming out of the ducts but the air isn't hot), the list of possible causes include:



Blocked circulation through the heater core - due to either sediment in the core or a defective heater control valve. Feel the heater inlet and outlet hoses while the engine is idling and warm, and the heater temperature control is on hot. The hose will not feel hot on the heater side of the valve if the valve is shut. The outlet hose will also not be hot.

With cable-operated control valves, check the cable for sticking, slipping (loose mounting bracket) or misadjustment. With valves that are vacuum operated, there should be no vacuum to the valve when the heater is on (except for those that are normally closed and need vacuum to open). Someone may have misrouted a vacuum hose.

With electronic heater control valves, check for voltage at the valve. It should have voltage when the temperature controls are set for maximum heat. If the solenoid fails to move when voltage is applied, it is defective and needs to be replaced.

If the heater core appears to be plugged, the inlet hose may feel hot up to the core but the outlet hose will remain cool. Reverse-flushing the core (forcing water into the heater outlet pipe with a garden hose) can sometimes open up a blockage, but usually the core will have to be removed for cleaning or replacement.

Air pockets in the heater core also can interfere with proper coolant circulation. It's akin to losing the prime with a siphon pump. Air pockets form when the coolant level is low or when the cooling system is not properly filled after draining.



Low coolant level - usually the result of overheating or a leak. A low coolant level can starve the heater resulting in little or no heat output. To check the level, pay no attention to the overflow reservoir. Shut the engine off, wait 20 minutes or so for the engine to cool, then carefully open the radiator cap. Allow any residual pressure to vent itself completely before removing the cap. If the coolant level inside the radiator is low, adding coolant won't fix the problem if there's a leak. Inspect the water pump, hose connections, radiator and engine for coolant leaks. Also pressure-test the cooling system and radiator cap to check for internal coolant leaks due to a bad head gasket or cracks in the cylinder head. Check the pressure rating on the cap to see that it's correct for the application, and carefully inspect the cap's gasket and spring. Replace the cap if it can't hold its rated pressure or has the wrong pressure rating for the application.

Cooling system neglect can allow internal corrosion to eat small holes in the heater core or where the pipes are soldered to the end tank. Leaks also can be caused by sediment circulating in the cooling system. Sediment is abrasive and will literally wear holes in the heater core.

A leaky core will often drip coolant into the passenger compartment (don't confuse this with water condensation that may be coming from the A/C evaporator). Leaks also can develop from fatigue cracks in the inlet and outlet pipes. This is caused by flexing of the heater hoses from engine torque and/or vibration.

Adding sealer to the cooling system may provide a temporary fix, but the long-term cure is to replace the heater core.



Defective or missing thermostat that allows the engine to run too cool. Maintaining the correct engine operating temperature (usually 200 to 220 degrees F.) is essential not only for good heater output but also for good fuel mileage and proper operation of various emissions control functions. If the temperature gauge on the dash reads low, the engine is slow to warm up or you can feel coolant rushing through the upper radiator hose when the engine is cold started, the thermostat is stuck open (or missing) and needs to be replaced. Be sure to install a thermostat that's rated at the same temperature as the original (usually 195 degrees on late-model cars).



Weak water pump that fails to circulate an adequate amount of coolant to the heater. This problem also will cause the engine to overheat. If the problem isn't due to a slipping drive belt, the pump probably has an eroded or separated impeller.

[MTL_4runner]

So now I am at the point where I am looking at buying a handheld borescope so see if I can identify whether the issue is actually in the heater core or if it is the return line that is somehow blocked (or perhaps even the water pump)....which a borescope should be able to show me. At least I'll have all summer to figure it out because I'm not going another winter without decent heat.

[oly884]

If it is the heater core, just be weary of any leaking. My buddy had his heater core go out. Granted he didn't have a toyota, but when it did, coolant flooded his inside. Maybe see if you can block off the heater core manually just to be on the safe side.

[MTL_4runner]

I don't think it's in any danger of getting a hole, I'm pretty sure it's probably full of rust dating way back to when I got screwed over by a dealer in AZ who was trying to force me to do a headgasket repair. They drained my coolant almost completely and then refilled it with tap water. I had to flush it many times to get it clean again but I'm almost positive alot of that got stuck in the heater core. I guess a borescope should settle that quite handily. Too bad they're almost $300 for a decent one.

[oly884]

Hmm, that's too bad. Just wanted to give you a heads up of what I've seen.

Are there any shops around the might have one that you could borrow/rent?

[MTL_4runner]

I was getting ready to change the heater core on my truck in an attempt to fix this issue but when shopping around places were asking $400-600 for a replacement heater core (while a radiator at 8X the size was only going for $200-300). I talked to a local shop specializing in fixing cooling systems and they mentioned they had a custom built flushing machine which they built especially for unclogging cooling systems full of rust, calcium or other deposits. It works by injecting a chemical solution into the system (they wouldn't tell me exactly what was in it), letting it sit for 3-4 hours, then it pulses the solution through the system in reverse. Anyway I got the truck back last night and despite a relatively cold night the heat from the trucks vents was outstanding (full blast was hotter than I could stand putting my hand on for any length of time). The service cost me about $50 + tax but it was more than worth it. I guess the real test will be come winter but I can safely say it was dramatically improved. :thumbup: I don't know why it took me so long to finally take it to a specialty place to have it flushed but if you have a similar issue, I'd certainly do this before resorting to replacing the heater core.

[MTL_4runner]

Follow up.....definately recommend the service above.
Truck's cabin is hot even when temps are below zero.

[fustercluck]

I regret that I didn't see this thread sooner, but when I flushed my radiator and core, I filled them with a hard water deposit solution such as 'CLR' or 'Limeaway' and water. I let it sit overnight and back flushed them both. It worked perfectly. I'd be willing to bet that if the shop didn't want to divulge their solution, then it was likely something you could get from the grocery store...either way, for 50.00 I'd almost rather let them do it regardless. Glad you were able to resolve the matter and were willing to keep us posted.

[93RunnerOtt]

Jamie,

I have the exact same problem (the one you had on page 1 of this post) - no heat in the cabin but the rear heater is fine. Temp gauge is where it should be, temp gauge does not pulse with engine revs. Head gasket was changed at 170kKms (Toyota paid), and again at 315kKms (Brad paid). Today I am at 355kKms, and no heat. thermostat was replace - no heat. Flushed core with CLR, a weekend with CLR, still no heat.

I was sitting on the edge of my seat reading all 10 pages hoping to get to the solution. ... I caved on Sunday and replaced the heater core - BTW, Toyota starts with a heater core and builds a car around it. The manual wasn't bad but stopped two steps before the heater core so had to guess the last steps. Got her all back together and, ... Still no heat.

Got some good pics though - here is what I can give back to the world after 7 hours of working with the dash of my runner:

[MTL_4runner]

Brad, sorry to hear about your issue and I'm glad I didn't go through 7 hrs of dashboard pain myself. So have you found why the heater core isn't working yet or are you looking for help on it?

If so I would check....
1) Let the engine get up to temp, turn on the cabin heat to high and see if both the inlet/outlet hoses on the heater core (on the engine bay side) get very hot. If one is very hot and the other is just lukewarm, you'll know the coolant isn't circulating properly.

2) Make sure the internal door control flaps for the climate controls are opening (cables - most models.....computer controlled servos - LTD)

3) Double check that the heater control valve is opening properly (I opened mine up and ran a garden hose through it to be sure there were no blockages in the system) .

http://img.photobucket.com/albums/v648/mtl_4runner/4runner/4runnercoolanthoses.jpg

If you have checked all these and you still don't have heat, you might have an internal blockage in the engine to address. We can cross that bridge when and if you get there.