Fluctuating Engine Temperature

I have a 2009 tundra 5.7 with 232,000 miles that has been basically flawless till now. Whenever I’m pulling a light or heavy load the engine temperature wants to go up, especially when driving conservatively, but if I accelerate aggressively to 2500 rpm’s it drops like a rock to normal. Due to the mileage I decided to replace everything; water pump, thermostat, radiator, horses, belt, tensioner and fan clutch. Still the same issue. I also checked the oil for water and the radiator for combustion gases and smoke out the exhaust. All negative. The mechanic can’t figure it out and neither can I. Any suggestions?

 

Fan clutch. Welcome aboard!

 

When you say the engine temp wants to go up, can you elaborate? How are you monitoring engine temp and how much is it climbing?

 

I’m using the temperature gauge on the dash. It will go from 12:00 o’clock (normal) to 1:00. Only when I’m pulling a trailer and the size doesn’t seem to matter. Accelerate quickly and it drops like a rock. Mechanic think it could be the transmission cooler now.
Never had a temperature issue ever even pulling the trailer with a tractor on it and 95 F.

 

That dash thing is mickey mouse compared to a tool that reads the ECU temps via the OBD2 port - look into that for a whole lot more accuracy about engine and trans temps along with everything else the ECU reads and uses to operate the vehicle. Luck.

 

What @Johnsonman said ^

Get a tool that will read actual ECT via OBD 2. When towing, my coolant temp will be a few degrees higher at lower rpm under load; if I drop down a gear at the same speed and load, it usually drops s few degrees due to (I’m surmising) the increased coolant flowing through the block.

 

How is the radiator cap? It sounds like the problem I was having. Bottom part of the cap broke off and lodged in the bypass pipe entrance. Its a common issue. See this thread:
https://www.tundras.com/threads/2008-tundra-5-7-temp-issue.59514/page-4#post-2778263

 

Thanks everyone for your comments and I will talk to mechanic about them.

 

In modern cars, there is only one coolant temp sensor and it feeds the ECU and that sends teh data to the instrument. Some do have two and am new to Tundras, so cant be sure. Therefore a scan tool will show the exact same data.

My belief is that you have an instrumentation issue. Years ago, before COP coils, we used to see coils that only failed under molderate to heavy acceleration. This is the area they are most loaded and produce the most interference. I believe that you have a bad sensor or wiring to that sensor that is causing the spike. Coolant sensors take time to chage readings due to thermal conductivity and don't really respond fast enough to "drop like a rock." I would find the wire going from the ECU to the temp sensor and test it. It could also be a ground issue if it is a single wire sensor.

Larry

 

Thanks Larry

 

It’s not showing signs of a blown head gasket?