jstecz,

The lines going to the rear heater core never get warm. I thought about disabling them--but first I want to figure out the front heater core issue. I would consider replacing the front heater core, but the heater core hoses never get warmer than around 130 degrees. And the radiator hoses never get hotter than about 160. I figure the coolant is not hot enough to provide much heat. If I ever get heat from the front, I am going to either disconnect or replace the rear core.

Can you answer my previous post about the direction of coolant flow? I've called several dealerships (in other states since there is only one dealer in Oregon and they don't answer my questions). None of the dealerships have helped--they just want me to make an appointment. According to several mechanics that have worked on the Montero, they say that the position of the thermostat means that hot water goes in the bottom of the radiator and cool water is supposed to exit the top of the radiator. This is different than any other vehicle I've owned and it's hard to believe it was designed like that. Just want to know if that is true for an '05 Montero.

 

My understanding is that the top pipe on the heater core is the inlet. I forget my reference for that, but that's what it is. My daughter has the car at college, so I can't look at the plumbing and verify.

I would blow out the heater core (both front and back) with either water or air. I would also blow out the metal piping going across the firewall.

 

Richard, I think based on all the work you've done you have positively confirmed that the heater cores are plugged. There is really no other reasonable explanation left. In your very first post you said that it is possible that PO used a StopLeak in the system. That stuff works for intended purpose (plugging small holes), but it can also wreck havoc with the rest of the climate control system (where passages in the heater cores are smaller than in the main radiator).

I've just checked my Montero, and yes - the coolant flows from bottom to top in the radiator. Coolant leaves the thermostat and goes to the passenger side where it drops to the bottom of the core. Then a hose from the top returns it to the engine. While this is different from many vehicles, it is not unusual. Many engine oil coolers and transmission coolers are plumbed that way too. Plus, this vehicle was engineered that way. Why? Who knows... Perhaps that way there is less of a chance of trapping air in the system or it may provide more consistent temperature for returned coolant. It doesn't matter because this is not the issue at hand. I think you have to go ahead and replace your old heater core. Best of luck.

 

Thanks for the reply. The biggest issue is why the coolant never gets that hot. If anybody has used an infrared thermometer to test the coolant temps, I would be real interested in the readings. Why does mine never get over 160 or 170 at full operating condition? And the heater core hoses never get over 130. The cores probably need replacing, but I don't think the coolant temperature is warm enough to put out much heat.

Since the coolant flow in the Montero goes from the bottom to the top of the radiator, why would the temperature of the top radiator hose always be the warmest? If it is flowing from the bottom to the top of the radiator, it would seem like the top radiator hose would be cooler than the bottom radiator hose. But it is just the opposite on my Montero. Any ideas would be appreciated.

One mechanic I spoke with said the Montero is designed to run cool all the time. He also said that there may be two thermostats in the inlet/outlet housing, but I can't verify that anywhere.

 

Ok.... I'm ready to eat crow...
After reading Richard's last post, I went out and tested my Montero (not just putting hands on the radiator hoses). I warmed up the engine and monitored the temps. Here are results:

Ambinet temperature - 42F
Coolant temp (as reported by PCM) - 188F
Upper radiator hose (measured by attaching a thermocouple to the back of it) 130-137F
Lower radiator hose (via thermocouple) - 85-87F

Here are my conclusions:
1. Coolant in these vehicles flows top to bottom through the radiator (I was wrong in my previous post).
2. The temperature readings off the radiator hoses is not a good indicator of the actual engine coolant temps.
3. I'm starting to suspect that you may not have good coolant flow through the engine.

With the item #3 in mind, here is the question - is it possible that the coolant pump is bad? You said you have receipts indicating coolant pump replacement. I wonder if it still possible that it is not working right? At the very least ask your mechanic if this could be a contributing factor to the issue you are having. It is possible that the pump is moving just enough fluid to keep engine more or less in the proper temperature range, but not enough to "push" fluid through the heater core.

I would suggest one more thing - go to an AutoZone or O'Reilleys and borrow their scanner. Plug it in and pull live data from the engine (with engine running). See what the engine coolant temperature is reported by the PCM. If it is high - then it is more likely that the coolant pump is not working well.

Not sure what else to propose.

 

Thanks for doing all the extra work trying to help me. I owe you a beer if you ever get to Eugene, OR!
Responding to your conclusions:

1. I've asked several mechanics (four shops have tried to figure out the heat issue). Two of them said that the coolant flows from the bottom to the top in the radiator and that is normal for Mitsubishi and some Hondas. They never could explain why the top radiator hose was hotter than the lower hose. I phoned an out-of-state Mitsu dealer and the service writer said it flows from the bottom to the top.

2. The most current mechanic used a scanner and said the coolant temp was around 185 degrees. But he said the scanner just reads the temperature at the sensor. So if the sensor is inaccurate, so is the scanner reading. Next he clamped the lower radiator hose to dramatically reduce the flow. He revved the engine and we waited for 10 minutes. The vehicle was already at operating temp since I drove about twenty minutes to get to his shop. Anyway, after 10 minutes with the flow restricted--no change at all. We both were expecting the temp to spike as the engine overheated. But it didn't. Then he clamped the upper radiator hose and got the same result--no change in temp. Bizarre or what.

3. The third mechanic suspected poor flow and determined the hydraulic adjuster needed tightening. He said that corrected the flow issue--but nothing else.

I'm going to use some Blue Devil flush and run the Montero for a few days. I'm also going to replace the rear heater core since it is much easier to do. I figure if the rear heat starts working, then the issue was bad heater cores. If that doesn't help, I'll just keep getting educated!

 

Man you are shutting down all my ideas just as they are put down

I think you have a good plan at hand - one more attempt at the coolant flush, then tackle the rear heater core. If swapping it results in a dramatic increase in heat output - you will know for sure that the front one is plugged too.

Here is another idea for why you have low heat output but "good" flow through the heater cores - what if you have a layer of calcium or some other gunk built up on the metal surfaces in the cores. Depending on the material it may significantly reduce heat transfer efficiency but may not restrict the passages completely. Alternatively, you may have few passages opened, so that fluid can flow, but have enough of them plugged up to reduce heat output.

Engine temperature reading does come from one sender. It looks like your readings are at about the same level as I got today. BTW, the gauge on the instrument cluster is getting the reading form a different sender than the PCM. I guess it is a backup in case one of them malfunctions.

 

HunterD,

Since our vehicle temps seem similar, do you have good heat front and rear? Maybe my coolant temps are normal and I just need the heater cores. Guess I'll find out in a week or two when I replace the rear core.

Did you check the temps for the upper and lower front heater core hoses by any chance?

Thanks

 

I do not have rear heater. Front was working full blast during the test - nice and toasty.

 

Just a quick update--turns out it was the heater core after all. I stripped down the Montero (removed consoles, passenger seat, stereo, display unit, instrument cluster, glove boxes, dash, etc and provided an $80 OSC heater core. The shop charged my $267 for all the rest of the work. A lot better than the $900-$1400 quotes I had been receiving. Finished putting everything back today and it works fine. The old heater core looked like it was in good shape and the service techs were confused that it still had good flow and did not weigh more than the new replacement. They said that the old cores are usually heavier since they have junk collecting in the passage ways. They also said that it was not necessary to remove the heater box, they had access to the core with the box in place. They also did not have to evacuate the A/C--that saved some money as well. In a few weeks, I'll tackle the rear heater core--it should be much easier!