Idles cool but overheats at speed... help?

Hey guys and gals. Greetings from Wisconsin. This is my first post on here so let me know if I'm an idiot and posted it in the wrong place.

I'm working with a 2002 Tacoma Xtra Cab 3.4L V6 TRD with 5 speed manual. So the engine is the 5vz-fe. It's got about 215K miles on it. Lately it's been overheating while I am driving. It will idle just fine at about 186 degrees but when I get under way, it starts to go up. I first noticed it on the highway a few weeks ago when I looked down and the temp gauge was rather high. I immediately rolled the windows down and turned the heat on and it went back down to normal and stayed their for the duration of my short trip. For short drives around town, it's fine and stays below 200 but if I get up over like 2500 RPM it starts climbing. I have never let it get in the red.

Here is what I know:

There's no coolant in my oil and no oil in my coolant.

The radiator is relatively clean, undamaged and unobstructed. The shroud is intact and in place.

The water pump has 10K miles on it from back when I did the timing belt. At that time I did a full flush and replaced the T-stat and some other things as well. All has been well since then, which was about a year ago. But a good few months of that were winter... so... yeah well cooling isn't usually an issue here in WI for those months.

It's not the T-stat. I just pulled it and did another very thorough flush. I had already purchased a new stat because I figured that was the problem. Before installing the new stat I checked it in hot water. It opened at about 193* F. I checked the old stat that I removed and it also opened as it should.

I have every reason to believe the temp sensor is accurate because when I flushed my system the other day, what I did was drain the radiator, drain the block via the little cock valve thing on the passenger side of the block, and also some more coolant drained when I removed the stat. I filled and burped the system with distilled water and went for a short drive. Then I drained it again, refilled it with distilled water and went for another short drive (like 2 miles at 50mph). I did it a third time. I really wanted to get all the old coolant out because I was switching from green to the pink "long life" toyota stuff. On all three of my short drives I watched the engine temp on an app on my phone climb right up to 212* F. As soon as it hit 212, my overflow started to bubble and steam. For anyone out there who cut class on science day, water boils at 212*. So all that said, I trust my temp gauge. I drained the distilled water and refilled with barbie blood and made sure to burp all the air out. As can be expected, the problem is not resolved as of yet.

My suspicion at this time is a faulty fan clutch. I have heard of people with 1st gen tacos having overheating only at highway speeds due to faulty fan clutch. I know this sounds counter intuitive due to the copious amounts of air flow from highway speeds, but hey, I've been surprised before.

Any and all questions and advice are very much welcome. I have yet to confront an automotive problem that I couldn't solve myself. But that said, I'm just a stupid welder, not a gear head.

I apologize for the lengthy and drawn out post. Have a wonderful day everyone! Thanks. -Justin

 

Very thorough Justin. Thank you for all the detail so we can help as much as we can.

I'm just going to throw it out there. Did you make sure the jiggle valve on the thermostat was properly oriented? And are you confident that you got all the air pockets out?

After making sure those two are correct, I'd agree that you probably have a fan clutch issue.

Anyone else want to chime in for someone who took an assload of time to make sure we had a lot of details?

@mechanicjon
@gearcruncher

 

Wow, thanks for the quick reply!! The jiggle valve is at the 6 o'clock position which I heard was "per the FSM". It's worth noting that when I first did my timing belt and replaced the stat the first time, the one I removed had the jiggle valve orientated at the 12 o'clock position. It ran just fine like that so when I installed the new one at that time, I installed it the same way. So the overheating issue started with the jiggle valve being at 12 o'clock and remained after I put it to 6 o'clock.

I am certain that I got all the air out. The system takes two gallons and it took them both. I parked it nose up at a very steep angle and ran it for a bit with the cap off, monitoring it until no more bubbles were coming out.

Thanks a lot for your fast reply, FirstTime! -Justin

 

I actually type pretty fast. It only took me one and a half beers to get my story told.

 

Just asking because I'd hate to miss something. When you burped, did you have the heater on? And did you wait until the thermostat opened up (maybe a couple times)? It seems that its pretty common (at least on this forum) for people to not get all the air out.

Moving on. If you'd like to completely make sure you got all the air out, you could use a vacuum filling tool for the cooling system, like a radkit (snapon) or airlift like this

https://www.tooltopia.com/uview-550000.aspx

I'm not sure of a good way to test the fan clutch other than just replacing. I have tests for the electronic ones I regularly work on, but not sure about these.

 

Yes sir, I ran it well up to temp with the heat on, burped it and went for a short drive and then parked it on a very steep incline (maybe 30 degrees) and ran it just to make sure. All done with the heat on. I've burped after I have done previous flushes in past days and have been much less thorough in the past without any issues back then. I wanted to make damn sure I did it right this time. Sometimes the best way to diagnose is to treat and see how the old girl responds. That being said, I purchased a new Aisin fan clutch yesterday which will arrive tomorrow. Easy to install. If that does it then great. If not... then I will go back to scratching my stupid head. cheers.

 

Usually a fan clutch problem shows up at speeds under 50mph. At higher speeds the air coming thru the radiator is sufficient to cool it. How old is your radiator. Sounds like a restricted flow issue. Either the water, do to plugged cores or the fins are clogged up with bugs.

 

I am not the original owner of this truck but presumably, the radiator is the original. It's not plugged up. I sprayed it out good with a hose. If the new fan clutch I ordered doesn't do the trick, I will definitely be turning my attention to the radiator. Thanks for your reply, Jon.

 

I was thinking clogged radiator as well. Try out the fan clutch first and let us know. Diagnosing anything over the net is never as easy as having the vehicle in person. Fingers crossed for the fan clutch being your fix!

 

Thanks for the reply, Roberto. As soon as I know something, Y'all will hear about it. I won't leave you hanging. I'm going to kill a few more beers and call it a night. later dude.

 

Hi Justin, to me this sounds exactly like a bad radiator cap. Your system should hold 13.9 psi roughly, water, especially water with coolant mixed in shouldn't boil as low as 212 at 13psi. This would explain why it cannot handle the higher heat load from highway driving despite airflow. I would get yourself a nice Stant brand cap or OEM cap to replace yours, also inspect the caps sealing surface on the radiator neck too just incase it has a crack or burr.

 

I worked at a performance shop for many years & worked on mainly imports. I also did basic maintenance & repairs. I was taught the jiggle valve or bleed hole should always go in the 12 o'clock position as it's main purpose is to help bleed air as air bubbles rise to the top. On most Hondas you had no choice but to put it in the 12 o'clock position as the gasket is molded to go in only one way in the thermostat housing.

That is until I got my 1st gen. For the 3.4L eveyone says the jiggle valve goes in the 6 o'clock position as per the FSM but the Haynes manual say 12 o'clock. Well I have a hard copy of the original Toyota FSM & sure enough it does say 6 o'clock but for the 2.7L it says 12 o'clock. I never understood as to why it would it should be 6 o'clock on the 3.4L but what the heck do I know, the Toyota engineers have their reasons & that's how I had mine.

I've also read online that putting the jiggle valve at 12 o'clock on the 3.4L makes it run hotter. I can't understand why it would affect coolant temps. Last week I changed my radiator. Pulled the thermostat out to check it & it still looked new after 170Kmi on it. Gasket was pretty hard so I replaced the gasket & threw the thermostat back in. Well I decided to put the jiggle valve at 12 o'clock this time to see what happens. Sure enough my temps are reading 10-15 deg hotter! WTF! Now that it has been a week & I've confirmed it's running hotter than the temps I was seeing for the past years, this week I'll put the jiggle valve back to 6 o'clock & see if my temps go back to how it always was in the past.

By the way, not sure if it's been mentioned but if your radiator cap is pretty old, I'd replace that first as it's cheap & easy. But fan clutch sounds about right in you case if you are confident that your radiator is not clogged. Wouldn't hurt to flush out the radiator, see if you get a bunch of crap coming out when flushing.

The owner of the shop I worked out would test fan clutches by hand. At idle with the engine at operating temp, he would try to stop the fan with his hand. He showed me on a car that had a bad fan clutch & he was easily able to stop the fan from spinning. Just ever so slightly touched the fan h his hand stopped it. Never seen him try it on a metal fan though. I'm not recommending you or anyone to try this though! I'm not sure how you are actually supposed to test fan clutches.

Edit: I type slow!

 

Thanks for your reply. I had given that some thought. My cap is marked .9 bar. So yes, basically 13psi. I assumed by cap was fine when my overflow was burbling but there wasn't a trace of steam coming from the radiator cap. I do have a working knowledge of boyle's law and you are correct. Under pressure, water should boil at a higher temp. I would have to ask though, pressure or no pressure, if your coolant is not boiling over, wouldn't it have the same cooling properties? My system boiled over with water. It has not done that with coolant. All things considered, a new rad cap is a cheap investment. Thanks.

 

This. Your water should not boil at 212 under pressure. Another vote for cap.

 

Well water effectively cannot cool anymore once it reaches the point of phase change, it's ability to further transfer heat away from a source is gone, but your system should be holding the water from going to the burp tank for a lot longer I would think.

 

My only other thoughts are maybe clutch fan, but at highway speeds those should hardly have to do anything at all, usually their symptoms present at idle where you seem to be fine. But there is always the lingering, maybe HG or cracked head. Mine went without dirtying the coolant or oil but still bubbled in the rad hoses a bit and raised temps.

But of course exhaust the other much cheaper options first as it sounds like you're doing.

 

Thanks for the info, Will. I just assumed that if they bothered to specify an orientation in the FSM, there must be a reason for it. sounds like you may have proved that the orientation matters. Seems like something that would be pretty arbitrary honestly but hell, what do I know.

 

how does the system simultaneously hold pressure while being able to expel coolant into the overflow when heated then suck it back in as it cools. The concept of the overflow is based on the system being able to "breath".... or am I totally stoned over here?

 

You are correct that water can no longer cool when it's undergoing a phase change. But I replaced the water with coolant and I am still experiencing higher than normal temperatures without my coolant boiling over. I don't know what temp the coolant I put in there would boil at and I would rather not find out. But if the coolant is not boiling over, shouldn't it be doing its job just the same regardless of pressure? I'm not saying you are wrong. just thinking out loud.

 

The cap has a spring loaded one (technically two as your gonna see here in a min) way valve essentially that blocks the passage of water to the overflow until 13psi is met. At that point pressure/expansion does its thing (pushing coolant into the expansion tank) until there is under 13psi of coolant pressure. Expansion means it essentially is still full at that temperature. If the system cools (as it should either at shutoff or during normal cooling cycling) the suction from the coolant losing volume will actually pull coolant back in from the expansion tank (burp tank/overflow whatever) through the rubber sealing flap on the spring loaded portion of the rad cap, so really it is one way pressure valve and one way suction valve as well, they just will never operate at the same time due to heat conditions (neither can exist at the same time and if they do call a physicist, a priest, and Mr. Toyoda himself). Ya dig? The expansion tank is actually really important in making sure your system stays full and doesnt puke coolant everywhere when it reaches operating pressure. Make sure your expansion tank has a good hose that reaches down into it too if you pull the cap off (sometimes they crack)