I purchased an '05 Montero a few weeks ago and it has very little heat coming from the front heater and none from the rear heater. The previous owner provided receipts for a lower engine rebuild from a couple months before I bought it. He had also replaced the timing belt and water pump.

The first repair shop back flushed the front heater core and checked the blend door actuator. They said a lot of junk came out of the heater core and that the radiator needed to be replaced. A previous owner probably used 'stop leak' in it and it has everything restricted. Replaced the radiator, thermostat and upper and lower hoses. A few hundred dollars later and still very little heat. I'm ignoring the rear heater issue until I solve the front one.

I went to a radiator shop and they flushed the system a few times and said there was plenty of heat coming from the front heater. He said it was so hot, he had to turn off the heat when he was test driving it. However, that was BS because it was barely warm air when I drove it home. The next day I went back and he said that the front heater core needed to be replaced--for around $1000. After some research, it does seem like an long, tedious process. I drove the Montero until the temp gauge was about midway and then used an infrared thermometer and the upper heater hose was around 136 degrees and the bottom heater hose was 145. The I shot the top radiator hose at 160 and the lower hose at 75. It seemed to me (not mechanically inclined) that the overall water temp is not as high as it should be and the difference between the upper and lower hoses was too much. Of course it is a new radiator and maybe it is very efficient. But still the heater hoses seem like they should be closer to the temp of the top radiator hose.

Took it to a third shop and he tested all the normal stuff and jacked the front end up 3' higher to try and burp the system. Looked at the blend door and the electronics and couldn't find any issue. He also back flushed the heater core and said that there was good enough flow and probably did not need to be replaced. He got similar temperature readings as me and then changed the thermostat (again). It was slightly warmer when I drove it home--but does not keep me at all comfortable in our current 25 degree weather. My wife won't ride in it because our feet and hands freeze and we have to wear heavy coats.

Any suggestions on other issues that might be causing a lack of heat? Any body else use an infrared thermometer and test their hoses to see what readings they get?

I'd appreciate any help. If I don't solve this soon, I'm sending the Montero to the auction!

Thanks,
Richard

 

My guess is you have an air pocket in the system.

On my 2002 3.5L there is a bleed screw on the top of the engine coolant piping. On mine, I could hear a water swooshing sound thru the heater core once the coolant would get past the air pocket. My symptoms were no heat at idle and slightly off idle, but heat during cruise.

 

The entire cooling system has been flushed and refilled three times now as well as jacking up the front end to burp the system. The radiator shop and the repair shop did not think it was an air pocket and I don't understand why the coolant temperature never gets over around 160 degrees. The weather here has been in the 20's and 30's, but after reaching operating temps, it is just barely warm air in the dash vents and cool air for the feet area.

 

The latest mechanic wants to drain the cooling system and put in some type of orange citric floor stripper. He then wants me to drive the Montero about 30 or 40 miles a day for three or four days. He says that will clean the block and heater cores completely. Has anybody heard of using this method?

 

Just jacking up the front will not clear the air bubbles from the system. You have to bleed the coolant with the two (I believe 10mm) bolts that are near the thermostat housing. Also, make sure you have in-cab heater on HOT when you do that

Before putting floor stripper into the system, I'd check to confirm that you have a problem with radiator being plugged with calcium deposits. You can open the radiator cap (when engine is cool) and see if you have significant lime deposits blocking the coolant passages. If you do, then perhaps the "floor stripper" is worth trying. If not, it is not going to do much.

In theory, the citric acid disolves calcium deposits and will clear some of the plugged passages. Never tried it on the vehicle, so can't vouch for it.

One more thought - do you have issues with engine overheating? If you have deposits blocking one heater core, then you would likely have the same issue in the main radiator and thus overheating problems.

 

Hello HunterD,
I wasn't at the repair shop when they jacked up the front end--but I do trust the two mechanics there and they are both knowledgeable. I will phone them later today and find out how he bled the system.

After the first shop ran several flow tests, they recommended replacing the radiator and I did. I don't think there is any blockage there. The floor stripper was more to clean the block and the heater cores. Since the lower end had recently been rebuilt, one of the mechanics suggested it could have some compounds in the passages and that using the floor stripper would clean it and the heater cores and not damage the new radiator. I'm putting that on the back burner until I receive more feedback. I'm concerned about damaging hoses and rubber parts with floor stripper.

The temps in Oregon are in the lower 20's to upper 30's and I have not driven the Montero more than 40 miles at a time. It does not overheat--it doesn't seem to get hot enough. Changed the thermostat 3 times (last one is rated at 180 degree). Replaced the radiator cap with the new radiator, thinking maybe it wasn't getting enough pressure in the system, but that was a waste also.

 

Based on your explanation it seems more likely that you may have the heater core plugged up or at least restricted. Since the radiator shop replaced your radiator due to poor flow test results, it is fairly safe to assume that heater core (also a radiator in reverse) may had the same affliction. You can try the floor cleaner. Talk to the mechanic who wants to do it and see what he says about how hoses hold up with that treatment.
The only other option is pulling the dashboard and physically replacing the core or pulling it out and getting it cleaned out outside of the vehicle.

 

The first shop said the radiator and probably the heater core had restricted flow. After they back flushed the heater core they said the flow seemed acceptable. The second shop also thought it might be the heater core and they back flushed as well and said the core seemed good. Of course, when I drove it, there was barely any heat. However since the temperature of the top heater hose hovers around 136 and the bottom heater hose is around mid-140's, I assumed water was flowing through the heater core--just not at the temperature I would have expected. I thought the water for the heater core was diverted prior to going thru the thermostat and should be closer to the temp of the top radiator hose (around 160-170)? I did check on some estimates for replacing the front heater core and they were north of $1000. I'll sell it before I invest that much in the heat!

 

You are right, water for the heater core comes off directly from the back of the engine without going through the thermostat. There should be two hoses going in and out of the firewall. I think it should be in the area near the brake master cylinder. I wonder if you might be able to take a temperature reading from them to see if you are getting return of the hot water.
This might be a dumb question, but is your climate control fan working?

 

I used an infrared thermometer and mentioned the temperature readings in the previous post (as well as the first post of the thread). That's one of the issues I'm concerned with--it doesn't seem like they get hot enough to provide decent heat from the heater core. Then again, if the heater core is blocked or partially blocked maybe there is not enough flow to encourage hotter water to move through and displace the cooler water. I'm not that mechanically minded--just trying to muddle my way through. Plus I really don't want to replace the heater core unless I'm 99% sure that is the issue.

I requested 2 of the 3 repair shops to check the controls/electronics and they both said they are working fine. The fan gets a bit noisy at the higher settings, but seems to work well enough.

Thanks for the suggestions.