Nissan Frontier overheating mystery

I have a 2002 Nissan Frontier with a non supercharged 3.3L v6. The truck is a crew cab, long bed and 4x4. I have had this truck since I bought it used in 2004 with 26k miles. The truck now has 196k miles and I have done a little modifying to make it a bit more off road capable.

I have done all the work to the truck myself, until last fall when I finally broke down and took it to a dealer, who was not able to find my problem, but I will get to that…
First of all, the truck has steel bumpers, a winch, a tool box, onboard air system and large tires, all of which make the little 3.3L work hard. However, for three years since I quit making modifications, the truck ran perfectly cool and the temp needle never once went above the normal operating position, even through thick sand at the beach, mountain trails and towing heavy trailers, until last summer.
Late last summer, on 90+ degree days, I noticed the temp needle would start riding above normal when I had the AC on. It didnt matter if I was on the highway, the city streets or idling in the driveway. When I turned off the AC the needle went back to normal. This started happening occasionally at first (once every 2 weeks) then towards fall it started happening more frequently, almost every 90 degree day. Soon after I noticed the problem, it would happen even with the AC off, but not get quite so hot.

After a few weeks of this, I started chasing the problem. I replaced the radiator cap, the thermostat (tested the old one and tested the new one before installing,) I took the radiator to a rad shop and had it boiled and flow tested, I replaced both coolant temp sensors, and then finally the water pump. When none of those repairs made a difference I built new radiator fan shrouds and that made no difference.
At this point I was starting to get discouraged so I borrowed a scan tool from a friend and drove around for a few weeks with it plugged in. I was reading live temperature readings of the coolant and verified that the gauge was working correctly. The truck ran about 200 degrees with the AC off most of the time, then, when I turned the AC on, no matter if I was sitting in park or driving on the highway, the temp would steadily climb until it got to 222 degrees and I would shut off the truck, at that point the needle was near the danger zone and according to several nissan dealership, the highest normal operating temp is 204, but it should stay around 195. At 205 degrees, the needle would start to move above the normal position, so the gauge seems to be fine.
As summer turned into fall, the truck started running cooler as the days began to drop into the 70’s. I finally got fed up with chasing my tail and took the truck to a dealer with my main concern being a blown head gasket or cracked head. The dealership inspected the head and tested the coolant for hydrocarbons and said that the head and gasket are not the issue. They advised that the only other thing it could be is my fan clutch.
After that dealership visit, the days were cool so I drove the truck all winter without changing the fan clutch. Then, 2 weeks ago, on a 70 degree day, I hooked up my truck to an empty trailer (maybe 1000lbs) and towed it 15 miles. When towing up hill with the AC on, the temp needle started moving.
I immediately went to napa and replaced my fan clutch. Confident that was the issue, I drove the truck to the mountains for a camping trip last weekend. While climbing the hills at 40mph and about 2500 rpm, the temp needle climbed to the near danger zone.

That brings us to today. I have exhausted myself trying to fix this problem, spent lots of money on replacement parts that made no difference and I do not know what else to do. I have posted this issue on numerous automotive forums with no new ideas. At this point, I can only imagine that there is still a head/head gasket issue and the dealership missed it, but my truck has not thrown any lean codes. I took the truck back to a dealership which is where it is now, and they can not find any issues and recommend they start with a coolant flush, which I declined because I have changed the coolant half a dozen times in the last six months. The truck is still sitting at the dealership and I don’t know where to go from here.

Any ideas or suggestions would GREATLY be appreciated!

You’ve got a good puzzler there. How about a stiff bearing like in alternator, AC compressor, idler or tensioner pulley, power steering bearing dragging the engine down? I’d check the timing if you have a light, what about compression test on all cylinders? What about a partially plugged cat preventing good exhaust flow, but not enough to affect performance ?

All good possibilities that I have not checked. Im on about my 5th alternator and this one only has about 15k on it so it SHOULD be good. As for the other bearings, I had all the belts off the pulleys about 5k ago when I changed the water pump and all pulleys were tight and spun freely.
I do not have a timing light but I double checked the marks on the timing belt during the water pump swap.
A compression check on the cylinders has not been done yet. I might suggest that to the dealership since I do not think I can rent a tester from auto zone. . I am towing a trailer to the dealership with another vehicle so that they can drive the truck under load Wednesday, which is forecast to be 85 degrees. The truck will most definitely run hot with a trailer behind it so I hope that will help them figure it out.

on most autos when you turn on the ac the cooling fan will come on. everything you described points to a problem with the fan not working right.

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Old pump which seemed to spin as easy as the new one

The truck

Roybus, the cooling fan does not change speeds when the AC is turned on and off. When I start the truck in the morning, the fan spins. It is a mechanical fan clutch and spins all the time. The new one is the same as the old one I replaced.

Is that the correct advance at idle? Does it increase properly with more rpm?


This may sound a little drastic, but I think you could benefit from an additional electic fan mounted in front of the condenser, if you can find the space.

You work the vehicle hard and perhaps it needs some help cooling down

At this point you might consider checking the ignition timing and making sure that it’s correct along with advancing. If the timing is retarded too much that could cause overheating even with no apparent symptoms.

Another possibility is checking for a converter restriction which has been mentioned as has the timing. A cat restriction can cause overheating with no apparent symptoms also.

A vacuum gauge is the easiest way to check for a converter restriction and the gauge can react in one of several different ways if a restriction exists.

I will check timing the timing next.

Oldtimer, I do not know what the correct timing is, I will try to find out.

Where does the vacuum gauge hook up to test the converters? My truck has two converters on each side.

Hook the vacuum gauge to a manifold vacuum source, preferrably off the plenum, not the throttle body. Here’s a good article about reading vacuum.

Once you’ve addressed all the coolant issues focus on horsepower issues. bearings on any belt driven components, timing, or compression. This baby just can’t handle the load anymore.

Thank you for all the suggestions. The dealer is going to drive the truck with a trailer behind it tomorrow, hopefully they will be able to diagnose it after that. If not, I will rent a timing light and check timing first, check all the belt driven pulleys, rent a compression tester and then a vacuum gauge. I will report back with any updates.

I know you replaced the radiator cap already, but everything is pointing to a defective radiator cap. Are you sure the new one was the correct pressure? Possibly is is an out of box failure. Also look for a hairline crack around where the cap meets the filler neck.

Is the coolant recovery system working correctly. Is the hose still hanging from the cap and have yo checked it for cracks? when the radiator is cool, the coolant should be all the way to the cap, no air space in the top tank.

Is it possible that the truck is running too lean under load due to a weak fuel pump or bad O2 sensor? A lean cylinder will run hot. I realize there should be other symptoms including fault codes, but I thought I’d add the idea anyway.

I also didn’t see if you’d changed the radiator hoses. Perhaps the old ones are collapsing inside.

I did change the radiator hoses. I only changed the radiator cap once and it was rated for the correct pressure, same as factory. They are cheap enough that I could replace it again, though, just to be safe.
The coolant system recovery does seem to be working correctly. I replaced one faulty o2 sensor at the post cat last year before this issue started because of a code keeping me from getting the truck inspected. The code was something like catalyst system cycle not working properly, I THINK it was code P0420, but when I changed that o2 sensor on bank 2 the check engine light went away and I have not seen it since.

It seems like you are on the case and doing a good investigative job on this. It appears to be a tough nut to crack. My initial impression – since you’ve eliminated the radiator, the radiator cap, faulty head gasket, thermostat, and water pump – is that either the radiator fan isn’t spinning as fast as it should, the ignition timing is off, or air remains in the cooling system. I’d eliminate all three of those before moving on to something else. Checking the intake manifold vacuum makes sense too as mentioned above, for an exhaust obtruction. After that … hmmm … I’d make sure all the routine engine maintenance suggested in the owner’s manual is up to date, and probably do a compression test, check the valve clearances, and check that the valve timing is properly aligned with the crankshaft.

If all that didn’t work, the next step, I’d probably order a new OEM radiator from Nissan. It may be that the old one is still clogged and can’t be brought to like-new condition even by your local radiator shop experts. Best of luck on this. I expect w/persistance you’ll have your truck back on the road in like-new condition in short order.

One final thought. Are you certain this isn’t just the temperature guage reading that is faulty. Is it possible it is reading higher than it actually is? Most modern cars have two temp sensors, one for the computer, and one for the guage. Have both of them been tested?

I replaced both of the temp sensors and the gauge seems to be working properly. I drove around for a couple of weeks with a scan tool plugged in and the needle starts climbing at 205 degrees and Nissan says normal operating temperature is around 194. At 222 degrees the needle is almost in the danger zone.

I have also taken lots of readings with a laser thermometer. The lower radiator hose is always at least 30 degrees cooler than the upper hose. Is that about normal?

Yes, that temperature difference is about normal. Have you run the vacuum test yet?

I have not run the vacuum test yet because the truck is still at the dealer. I think they are going to drive it one more time for a last look then I will go pick it up.