Civic - Honda :: 1998 Overheating - Temp Gauge Needle Popping Up Higher Than Usual

Well, I'm still driving the same old 1998 Honda Civic DX two-door coupe, and I've got a problem with overheating. The temperature gauge needle doesn't get quite to the red, but it's popping up higher than usual, and I'm concerned to see it getting anywhere near the red. It usually spikes when I get off the highway and stop at a light, but it also does it occasionally in a drive thru, and recently, I discovered that when I give it a little gas in neutral, it brings the temperature gauge needle down to normal.

Here is the history of recent repairs and troubleshooting:

-About 3-4 years ago, I had a leaky radiator replaced, so the one that is in there isn't very old.

-Last year I had a mechanic replace the thermostat, the radiator fan, and the radiator cap when I started having this problem.

-A few months ago, I had the timing belt serviced (the entire kit, not just the belt), but since the water pump looked fine and the car has so much mileage (275,000 miles), I opted not to replace the water pump. (I regret that now. I usually replace the water pump with every other timing belt, but I've learned my lesson.)-I've been to several shops to get a diagnosis, but they have a hard time getting it to overheat at all, so they can't diagnose it.

One guy suggested the water pump might be worn out (inside, without leaking outside). Another guy suggested that "if it was the water pump, you would know it's the water pump." Each mechanic has done a pressure test on the cooling system and a flow test on the radiator, and they all say they are fine. One mechanic theorized that I might have a very small head gasket leak, but nobody else thinks that is the case and there is no sign of coolant and oil mixing. Besides, the temperature gauge has never been in the red.

-One mechanic who tried to diagnose the problem recommended replacing the plugs, plug wires, rotor, and distributor cap. After doing that, it is running better than it was, but that didn't resolve the overheating problem. He also retarded the spark timing, but it is self-adjusting, so it re-advances itself after a couple days of driving. I can hear what sounds like minor knocking, but it's always made that noise since it was new.

-Everyone who has tried to diagnose the problem says the thermostat is opening and closing as it should, and the radiator fan comes on and shuts off when it should.

I'm done getting second and third opinions, and I'm ready to start throwing parts at it. Do you think I should start with the water pump? What are your thoughts? Don't tell me to replace the car. I just bought a new motorcycle.