This just happened today a few times and hasn't happened before. I had the airconditioner on in traffic. I was circling the block a few times in stop and go traffic. The engine started pinging during acceleration and my the temperature guage started to rise. When I turned the airconditioning off, the pinging stopped and the temp went back to normal. Is there any reason for this? Can I fix this (possibly with a new thermostat, waterpump, etc)? Also, I checked the coolant and there were no apparent leaks, and the radiator was full. Any feedback appreciated.

My first guess would be the thermostat since your cooling is adequate, but marginal. Probably unable to open all the way.

When I'm driving, even in traffic, my car doesn't overheat. It happened when the a/c was on in traffic. So your saying that it might not be opening up all the way. I'll have it replaced. Question, would it be ok to put a trd low temp thermostat? What would be the benefits/drawbacks to this?

Another possibility is your radiator is somewhat plugged up. The thermostat is the easiest and cheapest fix. Flush your cooling system while you're at it.

Your transmission shift points are tied to engine operating temperature. I would leave well enough alone.

Thanks. I appreciate your quick response. I thought using a trd one might help.

If you have a clutch fan I would check that too. They sometimes get loose and don't spin fast enough.

What happens? Do they lose the clutch oil?

There is a small electric fan in front of the condensor on the right side. Make sure that fan goes on when your a/c goes on

Murrs - This is a longitudinal-mounted engine. No electric fans by the radiator. The engine runs the fan.

Brian - I have an electric fan on the front of my a/c condensor, mounted on my raidiator. Truly.
Does'nt need oil tho, its automatic!

What year truck do you have? a '91? I have never noticed an electric fan in front of the radiator. That doesn't mean there isn't one. I have been told I am not the most observant person in the world.. :)

When I mentioned oil, I was referring to the viscous drive fan in front of the engine, driven by the fan belt.

Yeah its a 91 sr5, I know you were talking about the standard clutch fan, i took mine off and put a 12" thermo on. I think it works much better than the standard fan, runs a little cooler too.

LOL - I can't take into account accessories that didn't come with the truck.

Now I wonder what murrs was talking about...

In front of the A/C condensor on the right side of the car(passenger side) there is an aux. cooling fan that is for the condensor. I am almost positive it is on all rhe 4-runners from 1990 to current. I may be wrong about the newest ones. My 1995 4-runner has a stock electric cooling fan. This is not uncommon in cars that have fans running off of a drive belt. when you turn on your A/C your car creates more heat than the one fan can dissipate so it needs a second fan. If you remove the grill from the front of the car this fan is easy to see.