Best of Deals Car Reviews Repair Shops Cars A-Z Radio Show

Engine Temp High when in Traffic w/AC Running

I have a 1998 Honda Accord with about 170k miles on it. Lately, I’ve noticed that the temperature gauge creeps up to about 3/4 of the way to max when I’m driving in heavy traffic and running the air conditioner. This is the only time it goes past the midpoint, and it usually starts going up after maybe 15-20mn of sitting in traffic. If I turn the A/C off, the temperature immediately starts going back down to normal. Also, when traffic is flowing at normal speeds, I can have the a/c on for hours with no issues. The air conditioning itself is also pretty ineffective in heavy traffic situations. It gets very cold when I’m moving at a decent speed, but is pretty weak at low speeds.

I just had the radiator replaced about six months ago, and it doesn’t seem to be a coolant issue. Any other suggestions about what the issue could be?

Make sure all cooling fans are running as intended.

I agree. Check the cooling fans. If the A/C is on, open the hood and make sure both fans are running. The A/C should turn on both fans, no matter what the coolant temp is.

And the fans should be running with gusto, not just spinning lazily…Next, use a pressure-washer to clean the bugs and other debris out of the condenser and radiator fins…

A long overdue update:

The cooling fans are both running strong.

Since you’ve just had your radiator replaced and you know the fans are working, I’d next change the thermostat.

Possible contributors to your problem are
thermostat sticking
water pump weak (impellars eroded)
collapsed hose inner layer restricting flow
bad radiator cap preventing the coolant in the engine from being able to pressurize to increase boiling point.

T-stats are cheap to change. They can be tested, but it’s cheaper to just replace them.
Water pumps can also be tested. Erosion would not be uncommon for a puup this old…if yours ius original.
Hoses are cheap to replace.
Radiator caps are cheap to replace.

If it were me, I’d change the T-stat, the radiator hoses, and the radiator cap all at once and see what happens. They’re all cheap and all reasy to replace.

Since this started after the radiator was replaced, I’d be inclined to think that the new radiator is not the correct model or was not installed correctly. You should be about due for your second timing belt change. Its due every 7 years. It is normal to have the water pump changed along with the belt, so adding new hoses and a thermostat would be a good idea at this time. New heater hoses as well.

The replacement radiator may have been one designed for a non-air-conditioned model…Heavy-duty radiators have an extra row of tubes in them…

I don’t think the problem is the new radiator. That wouldn’t be my first guess. I’m assumng you have no newly developed engine problems you’ve noticed and no trouble codes (check engine light) flashing and the only thing you’ve done recently is replace the radiator with a new one and the coolant level is to spec and the mixture is 50/50 and there are no coolant leaks.

After checking the fans and assuming you find them working correctly, I’d probably take out the thermostat and test it in a pot of hot water to make sure it is opening fully and at the right temperature. Then I’d read up on the cooling system bleeding procedure recommended by the manufacturer and do that step by step. If that didn’t fix it, I’d come back here and ask what to do next.

One tip: If you find yourself stuck in traffic and it starts to heat up and you need to somehow stop it from overheating to the extreme, one thing you can do to help cool the engine is to turn off the AC and turn on the passenger compartment heater to max and the heater blower to max. It will be uncomfortable so roll down the windows, but it might just cool the engine enough to save you from a head job.

A couple years ago I replaced the radiator in an early 90’s Corolla and the third-party-non-Toyota-brand radiator I bought (new, for less than $100) from the parts store didn’t have nearly as many cooling fins on it as the original. I live in a mild climage where it rarely gets above 95 deg and it doesn’t have air conditioning and it has a manual xmission. So even with fewer radiator fins, it still cools the car fine. That’s why I don’t think the radiator is the likely problem on your car.

If you think it is the radiator, if you still have the old one, it is quite possible a local radiator shop could fix it for a reasonable price, considerably less than a new radiator from the dealer.


The timing belt was just replaced a year ago, but I’m not sure if they replaced the water pump, as well (this was right before I bought it). I’ll check the thermostat first. Thanks, everyone.

First thing I would do is top-off the coolant level and then “burp” all of the air out of the cooling system. There’s a little petcock there for just this purpose. If that doesn’t help . . . change the T-stat. Make sure nothing is stuck in your front grill, hard to see and could block any air coming in to cool the radiator. Rocketman

It’s normal for the temp gauge to rise with the AC on and moving in slow traffic. When the AC is on the condenser that sits in front of the radiator releases heat. This heat is then transfered into the radiator which causes the coolant temp to rise.

As long as the temp gauge doesn’t rise into red zone the engine is operating at normal temperature.