5vzfe hot at idle only, oddities
 

1997, 4x4, manual.

Replaced timing belt recently but don't recall if I did the tstat as well (was around 4th of July and also have done the same job on our 100 series since as well). ~315k miles. Not original radiator but not new to me.

Awaiting a script in a drive through, pull out and see we are overheating. Start to drive through the parking lot, my wife and I both crank the heat (front and rear) and we start to cool down, with hot air coming out the vents.

Get into traffic and stuck - start to climb in temps. Shut it down, light changes, we go and then stick again at next light - right as I'm about to shut it down we move.

Here's the odd part - heat system front and back are dumping cold air, not hot.

So we get to moving, start to cool down. Drive 20 miles on the freeway with no issues.

Pull off to get gas.

I'm 100% certain at this point it's a fan clutch.

Pop the hood - fan is spinning well, moving air - radiator cap is COLD to the touch.


Get home and we unload. Head back out 15 min later with an IR non contact sensor... gause starts to climb but the tstat is 168 on one side and 70 at the other.


The other oddity- the vehicle has done this regularly. The heat isn't HOT but is warm for sure. I had a parts 97 and the control slid another 1/2" or so and chalked it up to the cable has slipped at the heater valve (I can disconnect the cable and move the armature another 1/4" or so). But, the oddity... you can hear coolant flowing through the lines in the cab... in both the front and rear seats.


Otherwise the vehicle is perfect.


On my mind as possibilities are...
Tstat
Radiator
Fan clutch
Temp sensor


What throws me off are the varying temps in the climate control (cold air with ac off while overheating yet provides good warm air otherwise) and the fact that the radiator cap was cool to the touch after a 30 minute trip.

Thoughts?

Fan clutch tested? Might appear to pull enough air yet perhaps its not.

Has the space between the radiator and a/c condensor been cleaned out? Lots of debris can get between the two, especially if off-roading, causing poor airflow to an otherwise ok cooling system.

I'd be tempted to swap out T-stat (6 o'clock) and see what happens.

Heater valves often go out on these trucks, that may be involved too yet that t-stat and/or temp sensor.

Bottom line these trucks have Incredible cooling systems out of the factory. Mine can sit idling for over 2 hours in 105 degree central texas heat with the a/c blasting snow balls, yours should be able to do the same, especially in WA state!!! Luck and enjoy the Runner. :cowboy:

With the engine cold remove the rad cap and see if coolant is up to the cap. You may be low on coolant. What you described is a symptom.


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Low coolant, air in the system or bad fan clutch.

I'll check levels, I have a concern it might be a HG. Oil is clean, though.

The coolant overflow was overly full (about 2" from the top). When I did the timing belt job I used my snap on radkitplusa aut lift, so there shouldn't be air in the system unless there's another issue.


We dont offroad this vehicle. It had zero issues with temps when it was 80+ out but is having this issue, suddenly, in 50*s. There might be crud between the radiator and condenser but I doubt it would be an issue as it popped up suddenly.

Doubt the heater valve is bad, its mechanical for 1997 and seems to be functioning properly.

I do have extensive Toyota mechanic experience but these symptoms are odd.

I'm asking more to see if there are some T4R oddities that may be common. Had a similar situation in a 60 series but it ran like a sewing machine - wasn't overheating and had a very common gauge voltage regulator malfunction that causes the gauges to read wrong.

I did see that the gauge sensor isn't near the tstat housing so I might do another test and check with the IR sensor.

I'll also throw the OBDII reader/torque on it and see if anything looks off.

Does Techstream offer anything in addition to a standard reader? I do have it but is more of a nuisance than the reader.

Seen that exactly with low coolant.
Had a closed tstat but didn't cause engine temp to spike much. Did stop heaters from putting out heat.
Bad fan clutch a little different. Drove once 600 miles in low gear due to a bad fan clutch. High rpm and a good rad kept temps down until I could get to a place to get parts and replace it. Heaters were fine the whole time.
Ymmv

5vzfe hot at idle only, oddities
 

If you are low in the radiator, top both the rad and the expansion tank off. And watch your tank. The level should rise a little as engine warms up. If it doesn’t and you keep getting an air pocket in the rad look for a small leak somewhere.

With a properly sealed and operating cooling system air will collect in the upper portion of the rad at the cap. As the coolant expands during engine warmup that air and cold coolant pushes out of the center part of the rad cap and into the expansion tank. When the T-stat opens as the water starts circulating through the rad as it’s still expanding into the expansion tank, the hot coolant pushing through that center button of the rad cap causes a spring to swell and seal off that vent part of the cap allowing the cooling system to start building pressure.


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What a lot of folks dont realize is the coolant doesn't always pull from the coolant reservoir. I have seen this scenario before.

1] Really like others are saying low on coolant all the signs are there.

2] bad radiator cap and not building the pressure.

3] extremely dirty radiator and it cant cool down the antifreeze.


As a guess I would say its 1 or 2.

The cold radiator cap is really leaning to me like you are a gallon low on coolant.

If my memory is correct, these hold about 2 gallons of coolant.

So I hope this helps :)



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Bad clamps and a bad rad cap are the main culprit in my opinion on why the vented cap setup can’t maintain a full rad.


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This morning when cold the fan clutch had significant pressure, but not locked up. Assuming its fine.

Radiator was low. The cap looks awful. The overflow, as stated earlier, is overly full.

Warmed the truck up with the OBDII connected and IR in hand. Topped it off.

The ecu was registering right around 185. The tstat housing, after about 30 minutes of idle, never got above 140.

Increase in rpm, at idle, would see a slight decrease (2-3*) at the ecu.

With the system full the cap got warm but never hot.


So here's my possible diagnosis. Radiator is somewhat clogged and/or the tstat is stuck. This is causing a low flow issue through the radiator but not so bad that it can't maintain a temp via higher rpms (less of a 'moving' and more of a flow issue). Add a bad cap that allows increased pressure, allowing minor seepage and the ability for the overflow to fill, but not backfill.


So... new tstat ordered.

Fan clutch is being returned.

On Amazon the reviews for the Toyota radiators were awf. The Denso weren't much better. Local Denso was crazy expensive so I have a factory radiator from Toyota on order (less than a NAPA Denso, same price as NAPA brand) with a new factory cap.

I think you've already solved your problem. Mine sits at a solid 191 at idle all day long. 180's is perfect.

Well, not really. The issue has been temporarily fixed by refilling the void... the cause is still not 100% determined.


It isn't normal for an overflow tank to act this way. Might just be the cap but the radiator looks pretty rough.

Let us know your results. :]

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This...

“the tstat is stuck. This is causing a low flow issue through the radiator but not so bad that it can't maintain a temp via higher rpms”

When you are idling higher (driving) you’re getting more pressure from the water pump and it’s pushing past a stuck/obstructed thermostat. Had a similar problem on an old Honda Accord in high school.

I’d replace your cap know matter what. I bought three 3rd gens and all of them had bad caps when I bought them. They are cheep.

T stat stuck or not you should always have a full rad. The cap is the only thing that allows fluid flow in and out of the expansion tank.

It’s worth Looking for a small antifreeze leak around a rusty hose clamp etc. also.

A bad cap and leaks are the only reason coolant isn’t sucked back into the rad as the engine cools and the coolant shrinks in volume.


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