Truck runs hot
- Thread starter OzzyNF
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quicksilvr
New member
Unless you have an actual flow restriction somewhere, a slightly smaller radiator shouldn't make it run that much hotter. How much smaller is the radiator? Your best option would be to get a new Koyo stock replacement 4runner radiator for about $120. If it still runs hot with a brand new radiator, then you've got flow issues or fan issues.
Can you hear your fan kick on and roar really strong? If not, your fan clutch might be worn out and you're not moving enough air.
Can you hear your fan kick on and roar really strong? If not, your fan clutch might be worn out and you're not moving enough air.
If the truck is running really lean that can build up heat. However, I will put my money on the clutch fan.
Pikeman
New member
the engine running lean will cause it to run hotter. Smaller radiator should not be the issue. However if you are running green antifreeze instead of the Toyota Red and did not completely flush between that can lead to blockages. I say this because the red and green coolant are not compatible and can sometimes gel. My truck has been running hot ever since I did my Timing Belt water pump t-stat and just noticed the guy used green coolant. I am planning on doing a thorough flush and then going back to Toyota Red.
quicksilvr
New member
Yep. Coolant flows through it all the time, not just when the heat is on. (I guess I'm not 100% sure about that...but most other vehicles I've worked on it does)
Did you check your fan clutch? When my 4runner fan is on, it blows hard enough to make it impossible to do something like add ATF to the power steering resevior....the air is moving so much that the liquid blows like 3 feet. Ask me how I found this out.....:lmao:
TheDurk
Elite Member
Does it overheat only when stopped but is OK running down the highway? That is the giveaway for fan clutch problems. Listen for the fan roar and really strong air flow at startup. I just changed mine, the old one didn't do this anymore; the new one does.
I disagree on the heater core. There is a valve on the top of the firewall controlled by the HOT/COOL lever (manual A/C control) or by the auto A/C controller that shuts off flow to the heater core when no heat is called for. This is not going to affect your overheating problem. Most, actually all, vehicles I have worked on are this way (except only Brazilian Jeep with no heater at all.).
Why do you think you have a cooling problem? DTC P0172 is System Too Rich. (I don't have a DTC-P0175 in my '99 FSM.) Water temp sensor is one possible cause (because a bad one can make the ECU think that a hot engine is cold, and send more fuel than it needs). What does your gauge say? (I think gauge and ECU run off different sensors, but I am not sure on this). Are you losing coolant or is overflow tank bubbling?
P0172 could likely be an O2 sensor or several other things.
I disagree on the heater core. There is a valve on the top of the firewall controlled by the HOT/COOL lever (manual A/C control) or by the auto A/C controller that shuts off flow to the heater core when no heat is called for. This is not going to affect your overheating problem. Most, actually all, vehicles I have worked on are this way (except only Brazilian Jeep with no heater at all.).
Why do you think you have a cooling problem? DTC P0172 is System Too Rich. (I don't have a DTC-P0175 in my '99 FSM.) Water temp sensor is one possible cause (because a bad one can make the ECU think that a hot engine is cold, and send more fuel than it needs). What does your gauge say? (I think gauge and ECU run off different sensors, but I am not sure on this). Are you losing coolant or is overflow tank bubbling?
P0172 could likely be an O2 sensor or several other things.
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