Frontier 2000 2.4L King Cab 100K miles. Temp guage indicates overheating. Will intermittently spike then drop to normal. Engine does not "smell" hot or run rough at any time. Grab upper hose, you can keep your hand there, hot but not excessive hot. Lower hose is cool. Replaced temp sensors - no change. Replaced thermostat, no change. No leaks. Coolant is full. Borrowed OBD, and got temp reading while driving several miles uphill- engine running hot but within spec.

is the service engine soon light on?? if so what is the code??

The slow rising temp gauge points to a thermostat which has failed and stuck open. This is easy to replace.

At the same time the gauge will tell you if the car is overheating.

Is it losing coolant at all? A hot smell can result from leaking coolant getting on the exhaust manifold.

The smell can also result when leaking engine oil gets onto the exhaust. Camrys of that era had several characteristic oil leaks

- from the rear of the cam cover, especially on a V6
-from the distributor shaft o-ring
-from the oil filter-to-engine block mounting adapter (if fitted)

the oil pressure relief valve may be sticking causing a fluxuating oil pressure .this valve allows acess oil to flow back to sump hope this helps!

check your coolant level. half way on the guage is normal

is antifreeze dirty looking and if was changed was it chemically flushed?

every 3-4 thousand miles like oil if you want maximum millage and life for your engine

I have a question for you... is it in D or 4 cause D is the overdive gear on the truck and it does it for me as well.... its normal for that truck if you have it in 4 you shouldnt expierence that problem but we love our gas mileage these days lol

probably the thermostat stuck open, bad for engine, needs replacing

When an engine is overheating and then the temp drops on the guage, it's usually a sign that the coolant is not touching the temp sensor. There's no coolant in the engine. Putting water in the overflow tank won't solve this. Take the radiator cap off after the engine cools and put coolant in the radiator. you might have to crank the engine and do this several times, as the engine can develop air pockets that won't allow the coolant to travel inside the engine. If you don't see any leaks, and it still uses coolant, you've probably got a blown head gasket. Check for water on the plugs, check cylinder compression. If it slowly uses coolant, try putting a large box of pepper in the radiator or some of that radiator seal copper flakes.

Just a guess, but I would say this truck ran low on oil at one time. The result is the crank bearings took a beating. You may get away with just replacing the bearings and a rear seal. This engine is amost 'bullet-proof''! Frankster016