Hey guys. I have a 2003 Taco with 140K on it. 3.4L, 5 speed, K&N intake, aftermarket exhaust, throttle body spacer, spacer suspension lift (2"), and 32" tires. The timing belt and water pump were changed by the dealer at 100K, before I bought it.

This rig ran fine until a few weeks ago. I was climbing a light grade with the A/C on going 75 mph with about 700 pounds in the truck (including passengers). Ambient temp 85 degrees. Temp gage went about 80% of the way to the red, so I rolled down the windows and cranked up the heater. Temp dropped right to normal and I drove about another hour to the nearest auto parts store. Coolant was full! So I finished my 400 mile round trip having to use the heater a little here and there to keep the temp down without using AC.

I figured the pump has to be fine, so I changed the thermostat out for a new 180 degree (factory temp) thermostat. I replaced the same dexron coolant that came out, and it has the same symptoms. It runs FINE around town and stopped. If I climb a long hill it will overheat (maybe 1.5 minutes straight under load).

Any ideas? Auto parts stores won't sell an anti-collapse spring for my lower hose, so I am going to make one out of electrical grade copper wire (.080") and then heat/quench it to hopefully above 300MPa yield strength. I think it may be a possibility that my lower hose is collapsing, it isn't real tough to crush by hand.

Another question... Can I bleed the air out of the system by running the truck with the heat on and the radiator cap off? I can't find a bleed screw anywhere. I don't think there is much air in the system though...

Can you guys think of any other possibilities? I'm not loosing coolant and nothing is ever steaming.

 

Welcome aboard Rock.

Search is your friend on this topic as there are many threads around here regarding cooling....just remember to open up time range to a year or so.

Yes, bleed the air out by running with the cap off, heater on hot, fan on high and the front of the truck as high as possible topping off coolant a necessary.

Do you know the actual water temp you are hitting?

As for ideas:
1) Mud or other debris clogging the fins on the radiator. Take the garden hose and give it a good rinse being careful not to use too much pressure so as to not bend the fins.
2) Radiator internally is clogged and may benefit from a good flushing versus a dump and refill of coolant.
3) Since you suspect the hoses are collapsing, replace both the upper and lower radiator hoses with ones from the dealer...they are $10-15 each typically.
4) Fan clutch is not the likely culprit since you are running fine around town.

 

As sson as you said it overheatrs on the highway I was thinking new radiator......maybe mud in the fins too.

 

Drain out that gm dexcool and use oem Toyota red coolant. Check for cold spots on your radiator as this is a good indicator of being clogged.

 

Well I went home and drained the coolant again, and pulled off the lower hose. The copepr wire I had laying around was too high of Cu content to respond well to heat/quench hardening, so I increased the pitch of the spring to compensate for the softer material. I used WD-40 and string to pull the spring into the hose. Made it crush resistant to pretty substantial force with my hand, so I filled it back up and took it for a drive. Ran it with the A/C on, 2 passengers, up steep hills (accelerating in 5th and also in 3rd), and with the headlights and stereo on. No overheating, just a few minor variations to about 2/3 of the gage from the normal 1/2 way point that my rig operates at.

Auto parts stores should sell the springs....

 

I am having the same issue with my runner! it only overheats on hwy or under a load up hills. I have flushed the system and praying that my radiator is clogged. that is just too easy!

 

I took the rig for a nice long drive up mount hood... And it overheated again. So I still have a problem, although not nearly as bad as before. I am thinking I may have gone from this:

Condition 1 (moderate overheating)
Good factory thermostat
Bad collapsing hose

Condition 2 (mild overheating)
Bad autozone thermostat
Good hose w/spring

My next plan is to boil the old thermostat (factory one) and see if it does what it is supposed to. If it does, I am going to drain the coolant (arghhhh) again, flush the block and radiator, and swap thermostats back to the faactory one.

 

Not at all trying to insult your inteligence!! I had the same problem and out of the blue just noticed my fan spinning after i shut it down when it was warm. to make a long story short i replaced the fan clutch and the radiator at the same time.
My problem is currently curbed but its only been a week. good luck!

 

It has the same footprint of a clogged radiator. Flushing will not do any good. Nothing beats a brand new radiator with internals that are not rusted shut. I waited too long to replace my radiator that had this footprint....and I had to deal with a blown head-gasket because of it.

 

I boilded the old thermostat (factory one). It started to open a little at 190, and had about .25" open at 210 (boiling). On cooldown, it closep up tight before 180. Looks bad to me, but I have only tested a few over the years.

I would think that the coolant in a system with a clogged radiator would have debris in it. Like chunks of rusty material. It isn't like there is a filter in the system, and my fluid is very clean. Could the radiator still be bad? There isn't much of a way to test a radiator without cutting it in half, and they are so expensive. I don't want to do a $200 "test" at the auto parts store.

 

koyo radiators are just a little more than $100 and it sounds like many have had good luck with them. I'm putting one in mine next week.

 

That doesn't sound too bad if that is a 190 degree F thermo......I'm not so sure you will see debri in a clogged radiator everytime. Mine was clogged and had no obvious debri. For the Tacos I believe the radiators are closer to 130 delivered.....koyo brand. Saw them on ebay.