I've been having overheating issues with my 4runner. The head has been replaced, as well as the thermostat. But when you start the truck, the gauge is either at cold(left, obviously) or right in the middle. Then all of a sudden within 15 minutes of driving, it's near red

Does it sound like the gauge is shot or may something else be causing it?

Thanks

 

Are you saying it will start off in the middle even when the coolant is cold (like sitting overnight)?

 

Measure the REAL temp with an infrared temp sensor gun or mechanical temp gauge. The sender could be messed up...

 

Yeah, sometimes. A lot of the time, instead of gradually climbing as the coolant level rises, it goes from cold to middle, then on to red.

 

Where would be the best place to aim the heat sensor?

 

I would try the top of the radiator. If your truck has been sitting overnight and the gauge is still reading half-way, then the gauge/sender is definitely the culprit. Good luck!

 

That cast aluminum piece that the upper rad hose attaches to comes to mind. My aftermarket temp sender is in the upper rad hose and it reads a little hotter than the factory coolant temp sender (for OBDII) does so I'm guessing that upper radiator hose is pretty close to max heat for the coolant.

 

Thanks for the info guys!!

 

Aim the temp gun at the front of the head (watch out for the fan), get it as close as you can to the head casting and hold the trigger for a couple seconds so the gun will average out any irregular spots. Do not temp the rad to diagnose a cooling issue unless you are specically looking for rad temp. If the t-stat is stuck it won't be hot. If the gauge is jumping around it's likely that it's a sender or gauge issue.

 

Assuming the t-stat is working properly, wouldn't the top rad tank be the best representation of coolant temp (since that's what we're looking for) as opposed to the head/engine block which would not necessarily represent the COOLANT temp as accurately? Correct me if I'm wrong...

 

No but it's a good place to check if the t-stat is open. Actually yes you could get a good reading there (assuming t-stat is open) but we're really not concerned with the coolant temp, it's the temperature of the head that is more important, as this is what's being cooled- i.e; being kept from overheating.

KCRunner- Did whoever changed the head check to make sure that the steam holes are not plugged up? they're pretty small and I've seen so called "remanufactured" heads come with plugged steam holes.

 

Yeah, the head came from J&C Engineering, really clean. Actually, I should stated earlier that this problem was happening before I the timing chain snapped and the HG blew.