Overheating '02 Sable: Where to Start?

During trips in >90 F temps at highway and interstate superhighway speeds, I’ve noticed my '02 Sable LS [1] indicating temps than I’ve seen before. It’s never gone into the red, but it’s hit the top end of the white arc on the temperature gauge indicating the normal range. I can’t recall this happenning before.
Where would you look first? Fans? I’ve already verified the coolant level is within spec.

[1] It has the ‘Good’ V6 with the 24 Valves, Duratec label and 200 peak horsepower, not the base Vulcan-style V6 with the 155 peak horsepower.

The seven dollar thermostat should be replaced ASAP.

This is the first variable that needs to be eliminated.

The cooling passages could be getting clogged, but this would be the next thing to check after swapping in a new thermostat.

Then onto things like water pumps…

If you’ve verified the coolant, and the fans seem to be fine, the next thing I’d look at would be the water pump. When my '99 Dodge started spiking in the temperature department (and, IIRC, steaming from under the hood) it was like 4:57 on a Friday afternoon and I was 40 miles from home. Somehow, I lucked into finding an indie garage and the mechanic took an extremely long screwdriver, put the end somewhere in the front of my engine, and stuck his ear to the other end. After listening for about 5 seconds he said “you’ve got a bad water pump.”

I was still under warranty so Chrysler towed my vehicle to the dealership, and - sure enough - they had to replace the water pump.

The OP asked ‘where to start’. Starting with the water pump would be working backwards.

Thank you. I’ll pick up a T-stat on the way home… and drive real slow-like.

First off, have you removed the rad cap with the engine cool and verified that the coolant is full? Sometimes overflow tanks don’t refill the system like they are supposed to.

Replacing a t-stat is never a bad idea, but it is probably not the problem in this case. The op says the car o/heats on the highway at high speed. This rules out the fan, as the fan is not needed at speed.

There is a possibility that the water pump is the cause of the problem, but don’t bet on it. For this to be a water pump related issue, the impeller of the pump would have to corroded enough that the pump no longer moved enough water to the radiator for cooling. This is very uncommon.

The single most likely cause of your issue is the radiator is plugged either internally or externally. Over time, dirt, pet hair*, and other items can plug the airflow though the radiator. No airflow = no cooling. This shows up first when the heat load is the greatest. IOW on the highway at high speed. The cure for this is to clean the radiator and AC condenser. You can use a water hose, and blast high pressure water from behind the radiator to clear the air passages, or you can remove the radiator and holding it front side down drop it on the ground from about knee high. You will be amazed at the pile of dirt left on the ground after doing this. You will still need to clean the AC condenser.
for internal plugging, the radiator needs to be removed and sent to a radiator shop for cleaning. The shop will remove the tanks and run a rod though the core to clean out the deposits that accumulate in the passages over time. This is far superior to any flush that you might add to the radiator, and has the bonus of not being an environmental nightmare.
If you want to go with the take no prisoners get it done right the first time approach do this:
Drain the coolant and remove the radiator.
Dispose of the used coolant properly
Take the radiator to a shop and have them rod it out.
While the car is at the shop, take a high pressure water hose and clean out the AC condenser so it is clear.
Change the stat if you have not already done so.
Reinstall the radiator, and install the correct mixture of the correct coolant (they aren’t all the same!)

*People that keep large hairy dogs in their garage with their cars can get a blanket of pet fur on the front of their radiator/AC condenser.

Rick: Out of curiosity, what sort of price can one expect to pay to have a shop take out the radiator, disassemble it, rod it out, re-assemble and re-install?

For comparison, a new radiator for the OP’s car can be bought for $150-190 at the local DIY-friendly parts shop. Is it worth taking apart a five year old radiator? Is it sensible? eg: what are the chances that it’s going to spite you and spring a leak next month?

And for the OP, if you’ce concerned about the engine temperature, you do have a backup radiator in the car: Open the windows, turn on the heater to maximum hot and fastest fan speed. Yes, it’s absolutely miserable in August, but it’ll probably keep you going safely.

If you’ve got to drive it any distance before or on the way to getting it fixed, turn on the heater. I know its 90 degrees outside, but the heater dumps heat from the engine into the passenger compartment, thereby cooling off the engine at least a little bit.

Thanks for that tidbit.
For right now, it appears that not running it over 60 MPH will suffice.
I’ll take the scenic way home with the 45 MPH straightaway…

Well you are asking an apples to oranges comparison. In the remove and clean scenario, you are having the shop pull the radiator, in the replace it scenario you are not including labor. Last time I sent a radiator out it was something along the lines of $50 bucks to rod it out. The last time I bought a radiator it was about $200. Both of these prices exclude labor. There are some other factors I forgot to bring up in my last post. First off if the radiator is plastic rebuilding may not be an option. Also some plastics get brittle and crumble with heat and age. That last radiator I replaced, was due to it being plastic and external plugging. I could have cleaned the crap out, but it was 16 years old and the plastic in the neck was starting to crumble. Better to replace it was my call. I replaced it with an over sized brass tanked radiator. If on the other hand the radiator is brass, a rod out is as permanent repair as you can ask for. (assuming it is being done by a shop that knows their ass from 3rd base)
ETA: Also just turning off the AC will reduce the heat load on the engine.

The radiator has spares available on Rockauto.com for $90-120. Local prices will, of course, be higher.
Rick, seriously, thanks so freakin’ much for your help. You’re awesome with this stuff. If only I had an XC90 to ask about…

Here you go. :smiley: