Airlock, bad thermostat or heater core ?

[Mellemel]

What's going on with my 4rnr ? In the summer the heater blows very HOT. As the weather cools and the temp drops it blows cooler and cooler. Today it was -7c and it just blows cold ! The rear too.
I have burped the system as best I can a few times, again I get a few bubbles. When I leave the rad cap off from cold the coolant level is overflowing, it falls as it warms due I assume to the thermostat opening, I removed the rear heater core and flushed it, it was quite rusty in there, this gave some heat, but it's now blowing cold again. Is there any sure fire way to get the air out of the system ?

The IN hose to the main heater core on the engine bulkhead is hot, the OUT hose is not.

The top rad hose is hot the bottom hose is not.

The engine does not overheat, the temp gauge has never changed it's position in over two years.

Is it the thermostat that is sticking or stuck open or is it the heater core that's full of rust ?

Last winter was slightly warmer than now, but I have zero heat this winter !

I can start the engine in the AM and leave it for 20 mins to warm up with still zero heat, and then drive the 20km to work again no heat blowing out !!

Why does it blow so HOT in the summer and nothing now ?

I think my hosepipe is frozen right now so cannot do a flush of the heater core, by the weather channel I could maybe do it Christmas eve or day ! Forecasting +12c.

Anyone else here had the same symptoms and fixed it ? I'd love to get this sorted.

 

[4Runnermex]

What's going on with my 4rnr ? In the summer the heater blows very HOT. As the weather cools and the temp drops it blows cooler and cooler. Today it was -7c and it just blows cold ! The rear too.
I have burped the system as best I can a few times, again I get a few bubbles. When I leave the rad cap off from cold the coolant level is overflowing, it falls as it warms due I assume to the thermostat opening, I removed the rear heater core and flushed it, it was quite rusty in there, this gave some heat, but it's now blowing cold again. Is there any sure fire way to get the air out of the system ?

The IN hose to the main heater core on the engine bulkhead is hot, the OUT hose is not.

The top rad hose is hot the bottom hose is not.

The engine does not overheat, the temp gauge has never changed it's position in over two years.

Is it the thermostat that is sticking or stuck open or is it the heater core that's full of rust ?

Last winter was slightly warmer than now, but I have zero heat this winter !

I can start the engine in the AM and leave it for 20 mins to warm up with still zero heat, and then drive the 20km to work again no heat blowing out !!

Why does it blow so HOT in the summer and nothing now ?

I think my hosepipe is frozen right now so cannot do a flush of the heater core, by the weather channel I could maybe do it Christmas eve or day ! Forecasting +12c.

Anyone else here had the same symptoms and fixed it ? I'd love to get this sorted.

First: how did you burp it?

I've had this problem a few times when I install an engine.

Have you checked heater valve that has the cable coming from AC control?

Make sure the in and out are hot. That means you have circulation thru heater core.

It's can only be a few things..

It's starts with your burping method.

 

[tonytwopiece]

The IN hose to the main heater core on the engine bulkhead is hot, the OUT hose is not.

The top rad hose is hot the bottom hose is not.

The engine does not overheat, the temp gauge has never changed it's position in over two years.

Is it the thermostat that is sticking or stuck open.

From my experience, if the thermostat was stuck, or always open the vehicle would never get warm. The temp guage wouldn't rise above a few clicks on the guage. So that leaves it to a clogged radiator, clogged heater core or bad water pump. There are a few ways to test these components but you gotta do it with non-frozen fluid.

If you are not at the same temp on top and bottom hoses then the fluid is not circulating the way it should. Leading me to believe there isn't air in the system but clogged passageways. If you said the fluid is rusty then that rust could be what plugged up some lines in either the radiator or heater core. Air in the lines would eventually cause huge fluctuations in the temp guage and if you aren't seeing that then there isn't much air in the system. That, and air will eventually work its way out.

Bad thing is, you can really check both...unless you bypass them individually which would be a huge pain. I'd bite the bullet and replace the radiator, flush the system and add the new coolant to see what changes. You could flush your heater core at the same time again because there won't be a huge mess of fluid in the system...but I don't know your time/money constraints.

 

[jeremyc74]

It would help to know what the coolant temperature reading is in the ECU. The gauge is designed to show "Normal" and isn't accurate enough for troubleshooting purposes for something like this. If you can plug an OBDII scanner in that will give you the actual reading.

Once it's warmed up mine fluctuates between 184 and 188. No higher, no lower.

 

[Mellemel]

Thanks guys, well the temp gauge runs in the same position as it was two years ago when I got this 4rnr, so I think this tells me the thermostat is working.

I'm leaning towards it being a clogged heater core due to the temp differences between the in /out hoses. I hope to get it flushed this week depending on the weather.

Why would the bottom rad hose be cold though when the top is hot ? Does the heatercore outlet flow down to the thermostat ?

I am picking up a thermostat tmrw anyway, in case i need one.

The strange this is, after I burped it last night I did get some warmer air. This morning and all day I just got cold. Maybe there is crap/rust moving around !

I am noticing a drop in mpg too which can be attributed to a faulty thermostat. Due to operating temps not being reached so the ecu runs a richer mix, however the reduction of flow from a clogged heater core would produce the same results !

I will connect my obd11 also tmrw to check temps.

A new rad maybe in the pipeline too ! Pardon the pun.

 

[Drcoffee]

So have you checked the heater lines running under the truck to the rear heater? These lines rust out and slowly leak until they snap and flow out all the coolant. It may have started working better because you topped off the fluid after the core flush. The front heater core is high on the vehicle so as the fluid level drops, the engine is cooled but the heater core is not receiving fluid. If you are slowly losing coolant, the heaters core will go cold. How is your fluid level? I would suggest bypassing the rear heater lines up on the firewall.

Mine were weeping under the truck back by the heater core when I caught the problem. when I probed a little deeper the pipe just crumbled.

 

[Mellemel]

Nope, the underbody heater pipes look like they have been replaced at some point and are aluminum looking to me ! Not a sign of rust on them !! I have burped the system a few times now and the coolant level is good. The reserve coolant box is at the max line and stays there so I have no leaks.
So today it's +6c and I have nice warm air blowing, not hot, but comfortably warm. If it went to -6c there would be barely any heat blowing, this is what I can't understand !
After the drive home today, 20 mins...
the rad is hot
the top hose it hot
the bottom is cool.
The heater core, not yet flushed, that's tmrw's job, has hot inlet pipes but the out pipes are only warm, that must be where the blockage and problem is.
unless, the thermometer that's in is a summer temp rated one and opens at a different temp explaining why I have almost hot air today at +6c and not HOT when it's below freezing ! The engine just isn't getting hot enough to open the thermo !!??
My coolant temp showed 96c on the drive home today, temp guage needle is a tad below half.

I am going to flush the heater core tmrw and if that doesn't change anything I have a new Thermostat rated at 180f or 82c in case the one I have in is sticking !

 

[wc11]

Had similar problem last month. A new thermostat and rad, which were both original btw, fixed the problem.

 

[Mellemel]

A new rad will have to be looked at too maybe ! It must have been changed on a 97' you would think !

 

[Mellemel]

Flushed out the H-core both ways, no real rust or crud came out at all ! I by-passed the rear heater hoses too I think there was an air lock in there.

I have nice heat today but it is +8c right now. Forecasting -10c by mid week, we shall see what happens then !

It can only be, either be a bad rad or faulty thermostat ! I have good flow and heat thru the hoses except the btm rad hose which stays cool ! The thermo housing is warm however !

I had her raised up a good 2ft at the front to burp again, I'm pretty sure all air is out now.

 

[wc11]

A new rad will have to be looked at too maybe ! It must have been changed on a 97' you would think !

Not necessarily since I just did mine for the 1st time since new with 522,000km (324,000 miles)
but then I've flushed the system every 3 years since new.

 

[Mellemel]

522,000 km ! impressive. I'm only at 379,000 ! Needing a new muffler very soon, front shocks would be nice too. Have you owned yours from new ? I think I am the third owner.
Are you still on your original fuel filter, and pump, alternator and starter too ?

After today's driving the H-core "out" hose felt much hotter than yesterday !