So I was driving on the highway today when all of a sudden my temperature gauge started climbing. I had been on the highway for about 30 min. I pulled over on the shoulder and let it cool down. Fortunately I was able to limp home but i did have to pull over once more in a truck stop. Im not sure whats going on because in town the engine stays perfectly cool, even with 85 degree weather and me blasting the AC. I think this rules out my fan clutch. Any ideas? I was thinking maybe the radiator. Im gonna check the maintenance history to see if and when it was replaced.

How's the coolant level? Are you sure it's over heating or maybe just the gauge acting up?

Think it could be a thermostat? They go bad over time and it's a cheap fix. I would get another opinion on that because normally the thermostat going bad causes spikes, not a consistent high temp though...

Could be thermo. Could be radiator. Check your coolant and tranny fluid too and make sure they didn't milshake together. Could be the water pump too (a worn out one might not supply enough water to cool at high rpms, but be ok at idle and driving around town). When was it last replaced (every 90K with the timing belt is recommended)? Those are some of the easy things first.

You were lucky to notice the temp gauge.

Overheating is very common during the summer. Drain the coolant and inspect the inside radiator. You might have clogged cores.

I had the same issue in 2011 summer.

ahhh OP so how hot was it outside exactly?

The 4Runner should have no problem (in my experience) at 100F and HWY speeds. I would even bet that at 110F it should be fine.

Don't run the AC as that only makes the engine overheat more.

If it is overheating at 110F in normal driving conditions without the AC on then something might be wrong.

My bet is clogged radiator. Same thing happened in my '97 on the interstate. Out of nowhere the temp gauge started to slowly rise. Pulled over and let it cool down for a few hours. It cooled down, and when I continued on my trip, it got up to and stayed at normal temp. About an hour later temp gauge started slowly going up. Replaced radiator and problem went away.

I learned my lesson to never limp it home after an overheat. We had a mini van we did that with and I believe that since I limped it home I blew the head gasket and warped the head. If you overheat it's best to just get her towed and get the problem fixed. Hopefully yours is fine.

The damage was done during the over heating, not from driving it home while in normal operating temp range.

I'm thinking bad thermostat. Living in VERY hot Louisiana, have seen a lot of overheating problems. If thermo is stuck wide open, sitting in traffic and around town isn't too big a problem because RPM's are low and water pump is moving water at "normal" speeds, with slower flow at idle.

Constant highway speed means constant higher RPMs and constant higher water flow because the water pump is moving faster. Therefore, water is actually moving through that little radiator too quickly and isn't having time to cool down before reentering the engine and starting its voyage all over again. I used to see this problem all the time with "smart guys" who took their thermostats out to improve water flow because it's so hot and humid down here.

Could be wrong, but that's usually what happens down here when you've got a thermostat stuck open. Good luck!

Yeah, I'm w/ the guys on the radiator straw. Just replaced mine...overheating on the highway but great in town.

This doesn't sound right.

I have had the EXACT same problem for about a year now. It was fine when it was cool outside and around town/backroads, but got hot on the interstate with more load on it. It was usually fine as long as I kept the heater at halfway or hotter, but that got annoying. I replaced everything short of the head gaskets and radiator and it didn't fix it, even flushed it 20 or so times. It seemed to get a nasty buildup of what looked like red mud under the cap a lot so I assumed dexcool, I just got a TYC radiator from amazon, I havn't gotten to really test it but it seems to be working so far. Good luck with it, I feel your pain!

if the thetmostat is stuck open is what he is saying. if it is stuck open the coolant does not stop flowing and at hwy speeds it flows faster. when the thermosta t. closes the coolant stays in the little radiator and cools down untill the tstat opens again and cerculates the coolant. then the cooler coolant goes in the engine and the hotter coolant goes to the radiator and does it all over again.

That's because it's not.