I was in Moab a few days ago and did the chicken's corner trail. It wasn't to difficult, but I was going pretty slow most of the time. Being that I was 1000 miles from home, by myself and the trails are pretty rocky I wanted to take it easy. Because there was a ton of RZR UTV kicking up dust when passing me, I had my windows shut most of the time and the a/c on.

About 4 hours into riding I notice my temp gauge was starting to rise. I immediately shut off the A/C and the temp started to lower from 3/4 to about half. Normally it sits right below half and usually never moves after its warmed up. I pulled over and turned off the engine to see if there was anything going on under the hood and there was.... Coolant was bubbling in the reservoir, but not enough for it to spit out. I checked my temp gauge and it was right below half. I waited about 10 minutes to see if it would stop bubbling, but it didn't. So I started the engine to see if the bubbling would stop and it did. I was able to finish the trail without it getting hot again and still drove it around moab, arches and made it back to Portland today without any issues.

Throughout the trip on the trail I was getting whiffs of coolant smells, but I didn't really think it was that big of a deal. I probably lose less then a cup of coolant.

I use to drive this s-10 truck at my old job and when it was really hot out and using the the a/c I would hear the clutch fan getting louder. Isn't the clutch fan suppose to engage more when it gets hot in the engine bay? Because I sure didn't hear it getting louder on my 4runner. Is it possible I have a bad radiator cap?

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Strange. When's the last time you replaced the water pump? Also, every so often I try to carefully pump water and spray it from the inside out through the radiator. It gets pretty clogged up sometimes. I've seen people take like screen door material and put that on the body in front of it so that way it kind of catches large junk.

Is your clutch fan working?

The water pump was changed at 55,000 miles and it has 101,000 currently. But I had the timing belt changed at 75,000 because there was a bearing noise going on in the idler pulley, but the shop didn’t do the water pump because it only had 20,000 miles on it.

I changed the radiator 5 months ago for preventable maintenance and when adding new fluid I used a radiator funnel so it would get all the air bubbles out.

When I start my 4runner you can hear the fan pretty loud like most vehicles that have clutch fans for about 10 seconds of driving. It still spins when running, but is it spinning fast enough when it got that hot?

Changing the radiator as preventative maintenance seems like overkill/crazy.
I have a 2005 4runner with 150,000 miles and I'm on original WP, radiator, TB, and hoses. NEVER had an overheat or coolant problem. Of course, I raise the hood and look at the engine every week, and watch the ground I park on for leaks.

Last time my 4runner was on a "lift" I handed the mechanic a timing belt and he handed it right back and said mine was like new. That was 40,000 miles ago at 110,000 miles. The mechanic is a full-timer and sees new and used cars 6 days a week. Works at a place with 6 lifts.

Forget the preventive maintenance. Just change the oil every 5000 miles. Change the coolant every 7 years. If it ain't broke don't fix it.

Many 4runners out there with 500,000 miles.

Whatever you do, use discretion when taking advice from posters on websites like this one. All are bonafide experts, you know.

Had to replace those OEM hood lift assemblies one time 4 years ago. Went with some AM. Still holding up fine. Be careful what you replace OEMs with. Not sure where I got mine. Amazon.com: Customer reviews: Set of 2 Front Hood Lift Support Struts Gas Spring Shock for Toyota Landcruiser Prado 2002-2009 4Runner Lexus GX470 2003-2009

This is terrible advice. The third gen 4runners have a known weakness because the trans cooler is the bottom of the radiator, and there is no warning of a failure before you are mixing coolant and trans fluid and destroy your transmission. Bypassing the radiator with an external trans cooler, or preventatively replacing the radiator every 10 years or so are the only safe options.

I would rent the pressurizing tool from Autozone or Orielly, to see if the system is able to get up to pressure and hold it. Then go from there.

I beg the differ man! Do you have something wrong in your life to go on this rant to be judging me on my reason for changing the radiator? Yes the original radiator was in good shape and cooling just fine, but I don't want to risk the strawberry mikeshake being a 21 year old vehicle. I bet the mechanical handed you that timing belt back because he didn't want your business for being such a tool and bringing your own parts. Mechanics hate that.

I was thinking about doing this. That would suck if it's a blown head gasket.

Dude, check your radiator cap. Old caps are known to fall apart and the pieces fall into the radiator (spring and plastic cap). When this happens, proper pressure on your cooling system is now affected and is maybe the reason your coolant is boiling.

Pressure on the cooling system is similar to how a pressure cooker works. The higher the atmospheric pressure, the higher the boiling point of water which usually makes up 50% of your engine coolant. It's why pressure cookers cook food so fast because you're able to raise the boiling temp of the liquid the meat or whatever is cooking by increasing the pressure of the atmosphere above the surface of the liquid. Conversely, when you go to higher elevations, atmospheric pressure decreases and thus the temp at which water boils drops as well. At sea level, water boils at 212 degrees fahrenheit. When you're visiting the mountains for whatever, say your going snow boarding, and the place you're staying at is at 7,000 feet, it's going to take you longer to boil pasta because the boiling temperature is now a bit lower.

Because proper pressure isn't being held in your cooling system, the temperature at which it boils has dropped to whatever temp the water will boil at based on the elevation you're currently at. The city of Moab, UT sits at 4000 feet and then you said you were up wheeling on the slick rock so maybe you're now over 5000 feet. Without proper pressure on the system, your coolant would boil at around 203 degree fahrenheit which is easily attainable while you're wheeling.

If I was wrong about the cap, I'd suspect a head gasket issue. A compression test to find the compromised cylinder followed by a leak down test will confirm if your'e losing the compression into a cooling channel.

Some great advice on here except for the obvious, to which you've already managed to handle. The situation you were in is what I feared for myself when I'm out in the sticks hunting.

I ended up investing in an ultragauge just so I can actually see what my engine temp is, before that needle has a chance to rise. I read that once that needle starts moving up, it's almost too late and some damage has already been done, to what extent I'm not sure. Having an ultragauge also let me see what my average temps are and I've noticed I usually average around 186-188. In traffic, 100 degree outside temp with A/C on, worst I've seen is 196, but I dont live in higher elevation.

The reason I wanted to see what my average temps were in traffic while it was scorching outside, is if I needed to invest in an electric fan to switch on while I'm barely moving in traffic. Turns out for what I do, it was not needed.

Since I have a 96, I went ahead and installed a transmission temp gauge in as well. All for preventative maintenance. I believe if you own a 99-02 you can just buy a scanguage and it tells you everything all in one.

Definitely check to see if any damage was done by doing what others have recommended, then maybe invest in something to monitor your temps. Good luck!

Thanks for the info. I’ll just replace the radiator cap with a new oem and if it starts doing it again at slow wheeling speeds I’ll do the compression test.

Another thing I was wondering when the engine got warm, at what degrees does the A/T temp light come on?

Oh I was freaking out for a bit being 1000 miles from home when it started to get warm. But I wasn’t alone on the trail, so I knew I wouldn’t of been stranded. Because I had my hood up for it to cool down, at least 5 vehicles stopped to ask if I needed help.

I was averaging a speed of 10mph for the entire trip and half of that I was in 4low.

I was looking into one of those scangauges so I can see my transmission temps and figure out my gas mileage.


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I’d replace the fan clutch too. Mine screams for around 30 seconds before it gets quiet on a cold start this summer. It’s new, when I put the new engine in it got new everything for the cooling system.

All three 4Runners I bought had dead rad caps when I bought them. On all three the air purge part (center) was broken or missing preventing the system from building pressure.


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Screams for 30 seconds driving or idling?

At idle at first cold start. The milage on your rig and it still being the one from the assembly line I’d replace it as well. You already did the rad.

Replace the fan clutch and rad cap and have the confidence that unless it’s a failing head gasket you got all the bases covered.

PS a properly operating rad cap will purge all the air out of a cooling system in around 3 drive cycles.


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