Overheating trouble: fan clutch or radiator?

On 95+ degree days, when I'm stuck in traffic or rolling slowly uphill and even with the AC off, my 1998 3.4L Tacoma Prerunner has been seeing coolant temps up to 239 degrees Fahrenheit (measured on Torque Pro, the analog gauge is about 3/4 of the way to the top at this point). The coolant temp comes back down to the low 200 range pretty quickly if I can find an open space to cruise at 35 mph (but rapidly starts to heat up again if I encounter more traffic)

Based on TacomaWorld research, I thought it was the fan clutch at first, however:

• The fan is hard to spin when cold, and only slightly easier to spin when hot. There is no grating or roughness when I spin it by hand.
• There is no fore and aft wobble in the fan
• There is no silicone leaking from the fan clutch
• On an 80 degree day, I had some fun revving the car in neutral. At higher revs, the engine temp both cooled down (184 to 180) and there was a noticeable increase in airflow from the fan as the revs cranked up, so the fan seems to be working.

That leaves me with the radiator. I've patched it a few times, but it seems fine still. The overflow tank is full and when I take the pressure cap off when the radiator is cold, the fluid is up to the top of radiator. The fluid is pink and clear, and I had the waterpump replaced a few thousand miles ago with the timing belt. The surfaces of the radiator and condenser aren't very clogged save for a couple of dead insects and some pebbles - nothing major though. When the engine is very hot - 230 or so, I've popped the hood and I haven't seen any of the hoses collapsing.

It's fine on 70 degree days (192-194 degrees coolant temp), and the temperature generally sits below 200 degrees even on 95+ degree days as long as I'm moving at least 35 mph, though running the AC seems to exacerbate the issue.

Any thoughts? Could the radiator be bad internally, and is there any way to check? Thanks!

 

Did you check the t stat?

 

I haven't checked it yet, because I thought if the coolant temp was fine on the highway (will sit between 192 and 194 degrees Fahrenheit for hours), it meant the t-stat was working appropriately? Would you recommend a hot water test?

 

Either test it or just buy a new one. I’d think it would be cheap but IDK for sure.

 

I had similar symptoms, fan clutch fixed it. It seemed fine when turning by hand. I replaced the clutch and fan. Amazon has Aisin brand of both for a pretty good price and Prime delivery. Bonus is that the A/C works better now too!

 

Fan clutch should be turning on at 239°F. Would look at that.

 

Just chiming in here, my truck runs at 186 degrees all the time unless climbing a long hill.

 

There is a very good chance the radiator is plugged up behind the AC condenser with dirt etc and you cant see it unless you remove the radiator or the condenser.

Might be time for a new radiator at 125.00

 

The thermostat may not be opening fully, so you get enough flow most of the time but when you need maximum flow (above 200F) you don't get it and start to overheat.

Even a little dirt and corrosion on the radiator seems to insulate it and lower the heat transfer rate. Same for any buildup on the interior. Maybe just a few clogged passages on the inside.

I'd start with a new thermostat. The repair manual says to put the jiggle valve at the 6 o'clock position on the V6 engines. Toyota/OEM thermostats seem to be a bit bigger than aftermarket, and I'd recommend Toyota (without starting a debate).

If your radiator is old then you're not wasting too much by replacing it because the plastic will eventually start cracking. I know you said you already patched it.

 

Hi everyone, sorry for the late follow-up. I did end up replacing the radiator over Thanksgiving weekend, using the Koyo Radiator #

Koyorad C1755 Radiator

C1755. Similar issues to most people in that I could only get three of the four bolt holes to line up, and will have to drill a hole to secure the fourth bolt, but on the plus side, there is no longer coolant all over my engine bay and the temp has been staying between 188 and 194. Thanks for the advice and help here!

 

That’s good news! Last time I had an overheating problem my block ended up being cracked. That was my 86 turbo 4runner with like 300K+ miles, though.