slamigo

I have an 89 4runner that I found was not getting very warm when I turned on the heat. I noticed that there was coolant leaking out and it looked like it was coming from the water pump. So, I've since replaced the thermostat and the water pump. The coolant coming out was beautiful. Nice and green. I also changed the oil and while it was pretty black, there didn't appear to be any milkiness to indicate that coolant was getting into the oil. Hopefully, the head gasket is fine.
I had also replaced the heater control cables as the old assembly was cracked and you couldn't move the sliders properly.

Now I only get heat when the fresh air/recycyled air is set to recycle. If I do that, then I get lots of heat.
If I slide the selector over to fresh air, I get cold air coming in and the engine starts to overheat? What the heck is going on?

to sum up:

new T-stat
new water pump
coolant looked fine, oil looked fine

hot air if recycled
cold air if fresh air selected and engine overheats

I'm thinking that I probably didn't get enough coolant into it? Could this be caused by trapped air?

breknraj

Sounds like you need to do a full bleed of your cooling system.

Start with the engine cold, and the truck parked on a slight incline or ramps, front end up, and heater control all the way on. Take off your radiator cap, top off coolant, if needed. Start engine, and let it come up to temperature. You will probably see a drop in the coolant level when the thermostat opens. Top off coolant as necessary, until you are confident that the system is full, then replace the radiator cap and test drive, checking heat and watching your temp guage.

I think that this will solve your problem. If it doesn't, then you have some bigger issues going on.

slamigo

hmmm, come to think of it, I didn't have the heater turned on when I put the coolant in and idled it. I also didn't have to add any coolant as the level did not go down once the thermostat opened and the water began to flow a bit. Maybe I was too impatient. I'll try it again tonight with the front end elevated and the heater on.

slamigo

Okay, this is getting frustrating. I tried to 'burp' the coolant system, but there seems to be a blockage somewhere. Coolant is not flowing. I let it heat up pretty good, with the rad cap off. I squeezed various hoses to try and force some air bubbles to come up. The upper rad hose did not get very hot, but the other hoses (heater, etc) seemed to be hot. This is a brand new water pump and a brand new thermostat.
The rad is looking pretty crappy. The fins disintegrate if you brush them with your finger. But that would just reduce cooling capacity, not block it right?
I also noticed a little bit of chocolate milk under the oil cap. But I don't know how old that is. I've only had this rig for a few months. The previous owner redid the timing chain, I wonder if some coolant got in then. I just changed the oil and the oil looked fine. It was black, but there wasn't any milkiness. I keep checking under the oil cap but I haven't seen any brown foam since I changed the oil.

Where would be the most likely spot for a blockage? Also, I can't simply flush the rad right now as it's -20? C outside. The rad will have to be replaced very soon, but I was hoping to wait until the spring and nicer weather.
My other worry is the head gasket. My garage is not really insulated too well and it would not be too fun to tear down an engine in the dead of winter.

Any suggestions?

Yotapup

Could be a crappy Thermostat. Some new ones don't work. Check for blockage at lower Rad. hose.

slamigo

Well, I tested my old thermostat in a pot on the stove and it's working fine. Maybe I'll pull the new one out and see if it's working as well.
Why do these problems always happen in the middle of winter?

Yotapup

Wouldn't be any fun if it happened in the spring

slamigo

crap. I checked the oil cap again and there's chocolate latte there. There's coolant evident even on the dipstick.
The previous owner told me that he did the timing chain, but I wonder if he didn't change the cover? I'm guessing that it's probably been worn through by the old timing chain. I pulled the spark plugs and none of them seem clean. I'm going to pull the valve cover off and check out the timing chain guides. I really don't want to do the head gasket though. Hopefully the head gasket is not fubar. I'd rather work on that in the spring when it's warmer. It's gonna be -28 celsius tonight. I guess that's about -18F for you guys. yikes.