I have a 2000 Caravan 3.8L V6 with 117k miles. Always well cared for. All maintenance done on schedule, and recently had cooling system flushed.

Since the car was new, I make the same drive from San Diego to Las Vegas every year in the heat of the summer with A/C on and never a problem.

For the last 2 drives (last summer and now), my engine has overheated going up the 2 steep grades on the way. (There is a sign posted to turn off A/C on side of road.)

When I turn off A/C and turn on heater, temp drops to normal.

Never have any kind of overheating under other circumstances.

I've called several dealers service depts and received different answers. One that seemed the most confident said this is normal as engines age.

My question is this, is it normal for a high mileage engine to just start overheating (on hills in >100 degree weather) after 8 years of no overheating whatsoever under identical circumstances?

What would cause this, even if it is normal?

Thanks...

I' take a serious look at the radiator, have it flow tested.

You may need to replace the radiator, if you have not been using a 50/50 mixture of the proper antifreeze (G-05) and distilled water. The minerals in tap water build-up and ultimately restrict the flow and reduce the heat transfer rate in radiators.

The link below should help:

https://www.askmehelpdesk.com/cars-t...tml#post235973

You may also want to use 5W-30 full-synthetic engine oil and synthetic ATF (ATF+4). Synthetics have a higher coefficient of heat, allowing the engine and transmission to run cooler. Remember, the transmission cools through the radiator; therefore, consider installing a supplemental transmission cooler--it's a simple, inexpensive procedure. Overheating is always a serious matter on an aluminum head engine.

I've never had to add water or coolant, and only had the dealer flush the system. They recommend 90k miles.

Could minerals still build up in radiator.

An occluded radiator makes sense, as this problem just appeared last year, and ONLY occurs on steep hills in very hot weather.

Is a blocked radiator normal for a high mileage engine if I've never added tap water? I'm curious as to why this is happening now??

Can someone tell me what a flow test is, and who would do it? Should I head for a radiator shop and skip the dealer?

Thanks...