I have a 2005 model of Sienna with 154,000 miles. The car overheats once I switch on the AC over a short distance. With AC off the car runs smoothly. The mechanic has washed the radiator but the problem persists. Mechanic suggested we change the radiator from single cell to double cell. Please what do I do to solve the problem.. Thanks

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    Does the car overheat if it’s moving at highway speed still? (With the ac on) – sjfklsdafjks Nov 29 '18 at 18:01

First when the engine is cool check the coolant level. If the car behaves normaly without ac then the thermostat should be alright. Check for flow in the radiator: Start the car when cold run the car at idle till the fan comes on, the hose comming out of the bottom of the radiator should be getting hot quite quickly now. If not I suggest flushing the radiator. If the ac actually works, and the radiator is not clogged. I would suggest the following: Have a second person with you and run the car, like normal till the cooling fan comes on (Make sure it does). Then drive the car with the ac until the temp is just slightly higher than normal (don't let it overheat). Pop the hood and have the second person go out and check to make sure that both the main and secondary ac fan, is coming on. If not check the appropriate fuses and plugs. If they are both coming on or there is only one. Suggest motor/radiator flush.

  • Is there a distinction between a radiator flush and a motor flush? Or are they one and the same thing? I was about to ask the same question you answered before I decided to check if it has been asked before! – ElectronicsNewbie Dec 28 '18 at 1:17
  • Radiator flush only means doing the radiator. Engine flush means just the engine. A cooling system flush should mean both and heater core. – Michael Prokopec Dec 28 '18 at 4:04

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