Heating up on the highway

[4Runner4TW]

Having a weird issue. According to the Scanguage II the truck is getting pretty warm on the highway but cools down in traffic.

I'm located in Arizona where the past few weeks it was really hot.
So on the highway (65-75mph) the temp floats between 195-215.
But once i get off the highway it cools down to 188-193.

What would cause the truck to be hotter on the highway with all that extra airflow? The only time it cools is coasting downhill under engine load (it will drop to 180-184).

This only happens when it gets hot outside (90 and above).

Timing belt, water pump, Toyota thermostat, fan clutch, coolant, all replaced at the beginning of this year.

 

[gamefreakgc]

Lots of overheating threads lately! You're right, that exactly the opposite of normal operation. 215 is getting pretty hot especially if sustained. Even my e-fan never gets that hot if I tax the system real hard.

Flow is the first concern. Your water pump is new, so cross that off. Themostat is still potentially an issue, but not likely. You can easily remove it and run without one and see if that correct the problem. Some people have reported having the jiggle-valve in a different position makes a difference too, but it's not consistent.

Next thing to check is the radiator. When you remove the cap and look down the radiator, do the fins look abnormally thick and corroded? If yes it's time to replace it since corrosion will limit how much fluid can flow. Replacing the radiator cap is good maintenance as well. Another member just posted overheating problems and the spring and seal had fallen off the cap and was causing it not to pressurize the coolant properly.

 

[phattyduck]

Sounds like a stuck thermostat... (partially open) but that would be very unusual for a recently replaced OEM thermostat.

Incorrect jiggle valve placement would only make a 10-15*F difference in temps, and it wouldn't drop down to the low 180's unless you were coasting a very long time (down a 5+ mile hill).

-Charlie

 

[DaMonkey]

i'm sure it has more to do with higher RPM than speed.

maybe collapsing hose. either weakened hose can't keep up with with suck from the pump, or a bum radiator cap not releasing the negative pressure in the system?

 

[AntleredRuin]

i'm sure it has more to do with higher RPM than speed.

maybe collapsing hose. either weakened hose can't keep up with with suck from the pump, or a bum radiator cap not releasing the negative pressure in the system?

This makes sense to me right here. You can test this with the Torque Pro app while under the hood. Hold the throttle body open to raise the RPM and see if the rad hose collapses and the temps rise.

 

[LittleCaesar]

Was the tensioner replaced? Sounds like the water pump isn't turning fast enough.

 

[enapa]

i'm sure it has more to do with higher RPM than speed.

maybe collapsing hose. either weakened hose can't keep up with with suck from the pump, or a bum radiator cap not releasing the negative pressure in the system?

This was my thought as well.

 

[spartacus]

how old is the radiator? I agree with [MENTION=115347]gamefreakgc[/MENTION] you have symptoms of blockage in your radiator. At highway speeds the flow is restricted because the radiator cannot cycle the fluid volume fast enough but is adequate at lower speeds.

 

[4Runner4TW]

how old is the radiator? I agree with [MENTION=115347]gamefreakgc[/MENTION] you have symptoms of blockage in your radiator. At highway speeds the flow is restricted because the radiator cannot cycle the fluid volume fast enough but is adequate at lower speeds.

I was kind of leaning this way as well. I’ve had the truck since 2011 and have never replaced it.

 

[4Runner4TW]

Was the tensioner replaced? Sounds like the water pump isn't turning fast enough.

Had a shop do the work. Would have to check the labor sheet. However the part I worry about is the thermostat they installed was completely wrong. So I installed a new Toyota one and new hoses.

 

[LittleCaesar]

So it wasn't a Toyota thermostat installed? As Charlie stated,.start there first.

 

[TheDurk]

Had a shop do the work. Would have to check the labor sheet. However the part I worry about is the thermostat they installed was completely wrong. So I installed a new Toyota one and new hoses.

Jiggle valve at 6 o'clock, I hope....

 

[sakoluvr]

The 6:00 position for the jiggle valve is not an urban myth. It does make a difference AND my 2001 FSM indicates a 6:00 position. As an extra data point only, I went on a 500 mile trip this past Saturday with temperatures in the mid 90's. AC stayed on the entire time. Trip included some steep hills. My temperature stayed at 187 for most of the trip never topping 190. It hit 183 on a long grade where I was basically coasting without overdrive.

I put in a new T stat, hoses and a radiator a month ago with Toyota Red coolant.

 

[mtbtim]

The 6:00 position for the jiggle valve is not an urban myth. It does make a difference AND my 2001 FSM indicates a 6:00 position. As an extra data point only, I went on a 500 mile trip this past Saturday with temperatures in the mid 90's. AC stayed on the entire time. Trip included some steep hills. My temperature stayed at 187 for most of the trip never topping 190. It hit 183 on a long grade where I was basically coasting without overdrive.

I put in a new T stat, hoses and a radiator a month ago with Toyota Red coolant.

It's a fact the thermostat jiggle valve makes around a 10 degree difference in your coolant temp. I normally run in the high 180's to low 190's. But, if I hit a steep grade, I will see mid 190's. I think the highest I've seen on either of my 3rd Gens is 197 and that was climbing a steep grade in the summer heat. How you're able to not go above 190 is interesting. On both of my rigs I have newer radiators, newer fan clutches and the thermostats are in the correct position.

What I did find that was interesting is a new thermostat actually made me run a few degrees hotter and I suspected the new spring on the new thermostat was the culprit and I was right. I brought both the old and new thermostats up to operating temperature in a pot of boiling water and measured the distance the thermostat opened on each. The old thermostat opened further and I think that's just because the spring has fatigued a little over time from all the opening and closing it's done over the years. So, what did I do? I put the old thermostat back in because it's was enabling me to run around 4 degrees cooler. I carry the new one as a spare.

 

[sakoluvr]

The only ime it will go over 190 is at a light. It will jump to 191 or 192 sometimes. Drops back when I pull away

This is in my 2002 sport. My son's 97 runs about 3 or 4 degrees warmer

 

[LittleCaesar]

It's a fact the thermostat jiggle valve makes around a 10 degree difference in your coolant temp. I normally run in the high 180's to low 190's. But, if I hit a steep grade, I will see mid 190's. I think the highest I've seen on either of my 3rd Gens is 197 and that was climbing a steep grade in the summer heat. How you're able to not go above 190 is interesting. On both of my rigs I have newer radiators, newer fan clutches and the thermostats are in the correct position.

What I did find that was interesting is a new thermostat actually made me run a few degrees hotter and I suspected the new spring on the new thermostat was the culprit and I was right. I brought both the old and new thermostats up to operating temperature in a pot of boiling water and measured the distance the thermostat opened on each. The old thermostat opened further and I think that's just because the spring has fatigued a little over time from all the opening and closing it's done over the years. So, what did I do? I put the old thermostat back in because it's was enabling me to run around 4 degrees cooler. I carry the new one as a spare.

So I have to ask Tim whether or not the thermostats were identical in every way when dead cold?

 

[phattyduck]

What I did find that was interesting is a new thermostat actually made me run a few degrees hotter and I suspected the new spring on the new thermostat was the culprit and I was right.

My old one (OEM from ~2003) kept the engine around 183*F before I replaced it in 2017. One of the failure modes is probably opening too early. The thermostats are 82*C+/-2*C - or 176*f-183*F range. The slight variability at the outlet for a given thermostat is due to how much heat the motor is creating (and being absorbed by the coolant).

Hottest I ever saw was in Death Valley on a ~105*F day up a long grade with a leaking radiator cap (new, but not OEM) - it got to around 205*F. Not comfortable, but still safe.

-Charlie

 

[mtbtim]

So I have to ask Tim whether or not the thermostats were identical in every way when dead cold?

They seemed to be and are both OEM thermostats. I was just perplexed after replacing my thermostat that I was running around 4 degrees hotter. I think my theory of the spring tension easing up over time is the only thing that makes sense to me.

 

[aontkos]

Are you observing these temperatures with your A/C on? This will definitely warm up the ambient air prior to it reaching your radiator.

I noticed that mine gets warm on the highway, but only when the A/C is running. My truck usually runs 186-188°F in normal stop and go traffic but the temperature will increase by ~5°F with the A/C. When I'm on the highway the temperature will creep up to 198-202°F (at 2400 RPM) but immediately return to normal temps when off the highway. I noticed this yesterday and was considering doing a search about it, so it's convenient that I can just tag along on this thread. My temperatures haven't gotten high enough to raise any concern though...

I'm running a new radiator, new thermostat, new water pump, fresh coolant, etc.

 

[LittleCaesar]

They seemed to be and are both OEM thermostats. I was just perplexed after replacing my thermostat that I was running around 4 degrees hotter. I think my theory of the spring tension easing up over time is the only thing that makes sense to me.

I am going to go another direction with that and say that the new thermostat spring is used on other Toyo thermostats, thus saving Toyo some $$$ in material costs if the spring used in the old T stat was unique or slated just for the 5vz.