Hi

Heres a 22re question for the gurus. I went wheeling last weekend and as I was coming down from the mountain, I turned on the heater. Shortly afterward, the temp gauge started cycling from near overheating to normal, and it did that up/down thing almost exactly once a minute for about 100 miles. When I got back to sacramento, I turned the heater off and the temp was rock solid at 50%. Any ideas what could be causing the engine to overheat only when the heater is on? I was thinking that I was losing coolant, but the rad is topped off and there is about 20% left in the overflow.

Anyone heard of anything like this before?

 

search please this has been covered. dual stage t-stat.

 

how can he search for something he didnt know existed ? there is no such thing as a stupid question just stupid answers

 

This is kind of a neat problem (at least in my mind)....what happens is, the engine gets hot, the thermostat opens letting coolant flow into the radiator to be cooled where it then flows back around the engine picking up more of the engine heat and the cycle continues over and over again.

Now you go and turn on the heat letting coolant flow into the heater core. There, it's cooled by your blower...then the coolant drops in temperature and flows back to the thermostat closing it preventing the rest of the coolant from flowing so the engine temperature goes up up up until the pool of fluid near the thermostat finally reaches the temperature to open it up again.

The same kind of thing happens in my house. If you turn the heat on and close all of the doors, the heat stays on forever because the doors prevent the thermostat from ever seeing the heat that the furnace is dumping into the rooms. You need to have circulation and that's what a dual stage t-stat in your car gets you.

 

Duffdog- If this dual thermostat works for you then please update us. thanks

edit--- My gut feeling is if the cooling system is that finicky with just putting the heater on that a bigger main issue is behind it...and I'm thinking new radiator. .....a brand new one and not the rodded out ones that don't seem to be 100% there. That's just my gut speaking though.

 

additional note duffdog--- you said you went wheeling u in the mountains?....just make sure you don't have mud clogging the radiator fins.

 

Or other members calling answers stupid when it's better to have some one learn how to solve their problems via diagnoses and searching to find the right solution. "teach a man to fish feed him for life. give a man a fish feed him for a day"
oh by the way what did you have to add other than this to the thread????


also diffdog search for temp over shoot and look through 4crawlers site regarding your issue. i think he has the part numbers for the dual stage t-stat as well.

 

The part number for the dual-stage thermostat is 90916-03070

I see the issue mostly happening on the 4-runners with the rear heater.

Cures the problem every time.

Keep us posted.

 

Good reading below...this is exactly what's happening to yours.

http://www.4crawler.com/4x4/CheapTri...tml#Thermostat

 

I like the idea of the dual thermostat! I'll have to try it because my truck does the same thing in the winter when I use the heat.

I have a possible alternative solution, although it edges on the ghetto side. I used to have an '87 Voyager that would overheat because the thermostat would never open. Turns out air was being trapped under the thermostat, keeping it from heating up and opening. My solution was to drill a 3/16" hole in the thermostat to allow water to pass even when it was closed. Maybe this would work for the yotas also...

 

That's pretty common knowledge on the 22RE, but in our toyota's case...it's to always allow some circulation of fluid through the system at all times. The problem is just the system itself. The heater core dumps the "cooled down" fluid right before the thermostat. This makes the thermostat not open because of the cooler fluid temp, causing the over heat when the heater is on. I think it pretty amazing that just a small hole or the dual stage valve will keep just enough circulation to keep the temp in the right range.

The only downfall to drilling a hole is it takes the motor longer to warm up. In warmer climates one can get away with it, however in Wyoming you want a quicker warm up period.

How I know you ask?...

I've tried it and the motor just ran too cold in the winter. 22RE's like a warmer setting to acheive the most efficient combustion cycle.

 

Dang it, I thought I was being clever! That's what I get for being the new guy.

 

Haha it is pretty clever...that's why it's common! Most guys only drill about a 1/16" or 3/32" hole to prevent too much coolant from bypassing the thermostat though. I drilled a 1/16" hole in mine and when it gets below about 15 degrees I have to put cardboard in front of the radiator, otherwise I can drive all day and never see a reading on the temp gauge.

 

Ill try the dual stage thermostat first. Funny thing is that the truck didn't used to do this until recently. Before last month it was working fine even with the heater on.

 

Don't feel bad, cooling systems can be finicky beasts.
I ran into the same problem only after installing a new engine for a customer (along with a OEM t-stat), the problem didn't show up until after I did his first oil change. Even then it only showed up when driving DOWNHILL instead of on the 6 mile uphill drive).
Go figure.