Overheating with AC on in Low Speeds

My 2002 Nissan Xterra starts to show high temperature only when I run my AC in low speeds. My mechanic has replaced the Thermostat with an OEM part and replaced the Fan Clutch/Engine Cooling Fan Clutch. As soon as I was on the drive home from his shop and when I got to slower speed roads, the temperature started rising when the AC is on. I then took it on the highway and it went back to normal temperature. The temperature also started rising when the AC is on and it’s in idle. My mechanic thinks the next step is to replace the water pump although he said he didn’t see it “sucking air” or had any leaks. I must admit, my mechanic has overall been very good in the six years I’ve used him, doing many successful repairs. He is however, very busy as one of the most referred in town. However, he doesn’t speak English well but I can eventually understand him when he repeats things. I am now about $600 in on repairs and I want to make sure I can have him focus on the right things and not waste more money and time. I have noticed a few things to check from my research include the AC compressor, the Cooling System, and Clogged Radiator. Can anyone give me some input on what I should have my mechanic check or provide me any other guidance? Thanks so much!

Has the mechanic checked if there’s debris blocking the condenser?

Because if there is, the heat the condenser transfers to the radiator will cause the coolant temp to rise at slow speeds because the ram air effect from the vehicle moving is lost. And the fan by itself can;t move enough air to prevent the temperatur from rising.

If the condenser has debris, flush the condenser with water.

And don’t use a regular nozzle and hose to flush the debris from the condenser.

This just pushes the debris from the condenser into the radiator.

Instead, you want to use a spray wand designed to flush the condenser of debris.



Thank you Tester. If it’s on the front of the vehicle I pointed a light on it and its didnt look as bad as the pictures but I’ll have him check it.

Testor’s cleaning of the exterior of the condenser and radiator would be a logical next step.
If that doesn’t help, then I think removing the radiator to flow test is the next step. On a twenty years old vehicle I would not be surprised if the radiator is partially clogged.
Water pump impeller could be bad after 20 years, I do not know if the impeller material corrodes or not.

I think your mechanic is on the right track. 20 year old engine, lots of stuff can start to start not working entirely right, could lead to overheating in certain driving situtations. These are the sorts of things I’d be looking at if I had similar problem.

  • Is coolant at correct level, and in good condition, proper 50/50 mix?
  • Does cooling system and pressure cap hold pressure and regulate at the correct psi?
  • Does air flow freely through the radiator and A/C condenser?
  • Does coolant flow through the radiator as freely as it should?
  • Are radiator cooling fans spinning when they should, and at the correct rpm?
  • Is water pump moving coolant through the cooling system at the correct flow rate?
  • Are there any signs of engine exhaust gasses getting into coolant?
  • Is AC compressor turning as freely as it should?
  • Any signs of ignition or valve timing problems?
  • Any signs of engine air/fuel mixture problems?

Thank you Purebred

Thank you very much, do mechanics have diagnostic tests that would test for these things?

It seems like the consensus is that with a 20 year old engine issues can arise. I have been fairly acceptant of the fact that if I want to drive a paid off beater vs. a newer car with payments that I would have to stay on top of maintenance. I know of people who are driving old cars, as old or older than mine. And they seem to be doing it fine. Another reason I want to keep investing in my car is that I had a brand new transmission (not refurbished) 30K miles ago and I was told I could probably get 100K more miles with a new one. That said my starting price range for a newer used car seems to land around the 150K mile range. If I have a car right now at 190K, it seems like my best option would be to keep trying to fix the issue rather than starting another maintenance cycle and likely spending more on purchasing a car. I would probably be willing to spend several hundred more to fix my car if the issue could be fixed although if it can’t be fixed then I’m curious when I should give up. Could be something my mechanic could hopefully be straight up with me instead of keeping going down rabbit holes. What do you guys think? Could this issue be fixed and with my situation do you think this strategy is justifiable?

Just my opinion you have a vehicle that you know, buying a vehicle that you do not know with 150K on it would assume more risk.
In todays used and new car prices, I would think keeping your Nissan is the better course if the rest of the car is in good shape.
However a few more things, have a compression check performed to ensure rings and valves are in good shape. With the overheating, the transmission fluid needs to be changed now, transmission fluid should be changed every 30-50K miles.

My guess new radiator and water pump will result in a fix, I would have the upper and lower radiator hoses replaced at the same time.

Again, a guess, all the above would be less than six months payments on a used replacement vehicle that may require costly repairs.

Only you and your mechanic can answer that.

Like the old cliché “better the devil than the devil you don’t”

I’m unclear on if you have a 2 separate radiator fans or a 2 stage fan but the obvious first step is to let the SUV warm up at idle, fiddling with the AC on and off, observing when and if the fan(s) come on.
If it’s a 2 stage fan like I suspect and you’re lucky, it may simply be a bad relay or wire connection.

Thank you so much for your input Purebred. Very grateful for this perspective. I believe I replaced my radiator about 40K miles ago. Do you happen to know if there’s any sort of average life span for them? Again, I’m sure there’s so many factors it can depend on and as you said if it solves the problem its better than the unknowns of a new vehicle. Thank you again!

Hi Beancounter, I believe when I looked there was just one fan on the back of the radiator facing the engine. I took some time to try to see if the issue had predictable symptoms/characteristics. I drove it for at least 20 minutes in a residential area at an average speed of around 18 mph with the AC on. The temperature started steadily rising. Then I decided to try turning the AC off under the same conditions. The temperature dropped to average but in a span of about 5 minutes rose to 2/3 and then when I was down to a very slow creep went uo to the H mark. Then I took it on the Highway at up to 75 MPH and as soon as I was accelerating to higher speeds it went back down to normal. I then tried putting the AC on and got off the highway and it started rising again. So bottom line is it seemed like there was a correlation between the heat increase and lower speeds. It seemed like there may have been a correlation with use of the AC but at one point it was rising when AC was off as well. So just some added insight if it helps with additional insight. Thank you so much!

Well, it looks like you need to through George San Jose’s checklist but the nice part is that much of the list you can do yourself and get a rough idea of what’s going on, with a little “How to?” from Google and a generous dash of common sense safety.

It’s hard to prioritize here what to do first. An experienced shop’s visual inspection is the best way to decide the testing priority list. Cooling system pressure hold and if there are exhaust gasses in coolant are two tests definitely worth considering. If the second test fails, that’s probably a show stopper. If you feel lucky, could try just replacing the cooling system pressure cap.

One thing you’ve got going in your advantage, presuming you live in N. America, cooler temps on the way, so won’t have to use AC as much. 20 year old Nissan, 150k miles, hmmm … if you have to pay a shop their hourly rate for everything needed to keep the car well maintained, I expect it’s going to soon start to become a financial burden. I have two vehicles, both older than yours and both w/ more miles, but I do the repairs and maintenance myself, driveway diy’er. Suggest to try to negotiate an arrangement with the shop, where you agree they do all the work they recommend, and in return they offer you a discount on their hourly rate. They may be able to agree to such a deal b/c they can better plan their work schedule and ordering of parts more efficiently. Emergency rush-jobs more expensive for a shop to deal with than " please bring your car in for some routine maintenance jobs, plan to let us have it for 3 days".

Thank you so much for this feedback and Ideas. Very valuable and I so appreciate you taking the time. Do you mind sharing what you think is important to do for yearly maintenance? Do you have any idea of what it costs you for each car? Ultimately I’m still leaning towards keeping the car until it’s very clear it’s all done. But this really helps me to do a better job moving forward. I may invest in some DIY equipment at some point as well. But with my schedule I work a lot and sometimes the Overtime I make may justify me paying rather than DIYing. Thanks so much!

Thanks again for your input!

Why did you replace radiator 40k miles ago? 2-3 yrs ago?

Since the mechanic replaced the fan clutch its a good bet this vehicle has the mechanical, belt driven fan.

It overheated at that point and that’s what my mechanic suggested. Same mechanic I still have. That was five years ago and I have owned it since 2013. I didnt have any prior maintenance info from the prior owner so I am assuming that it was due to be replaced at that point… From that poulint until now there was one instance of overheating 3 years ago. He replaced the radiator hoses and it solved it? Do you have any input regarding this info? Thanks so much.

I follow the manufacturer’s recommendations for the most part. Engine oil and filter replaced every 5,000 miles, brakes inspected, replace worn parts, replace engine coolant every 2 years, spark plugs replaced every 15,000 miles along with the other tune-up items & adjustments, rinsing exterior of dust with garden hose once a week, clean exterior with warm water and soap once a month, and apply wax twice per year. Vacuum debris from hvac air-inlets (bottom of windshield). Lube door hinges, trunk lid, and hood, and hood latch. There’s other stuff as part of routine maintenance, but that is done when it appears from inspection it is time to do it, or when diagnostic alert is shown on dashboard.

For the needed parts and supplies, I’d guess about $50 per month for both vehicles.

Note: what I do for my older cars likely differs from what’s needed for your newer car.