93 Nissan Maxima.

Symptom: engine overheat. Coolant leakage found on the ground beneath
timing belt. Checked thermostat and didn't found any leakage around the
housing. But the overheat is not due to coolant leakage I guess because
the leakage is not that serious and I refilled it right before the
overheat.

I changed the thermostat a month ago (it was stuck open slightly).
After the replacement, I think it worked well (temp reaches half of
the range and stops right there).

But in the recent couple of days, engine starts to overheat.

Another symptom: on highway 101, I was on the #1 lane, and suddenly I
noticed that the tempreture was near the red range. I changed to the
emergency parking lane in 5 seconds and the temp gauge dropped sharply to the normal
range even before I stopped the car. What could be the problem? It never
happened before I changed the thermostat though.

 

well, worse comes to worse, take the thermostate back out and put it in a pot and fill it with water. boil it and see when it opens. it should open at about 190 F if its not defective. but thermostates are cheap, replace it again for ****s and giggles. i hope its not your water pump... g/l

 

Sounds exactly like what happened to me before I had to change my water pump....It's hard to do, but it's doable...It just calls for downtime and the right tools. Let me empahsize...MAKE SURE YOU HAVE THE RIGHT TOOLS!!!

You can get a water pump from internetautomar if you want to...It shouldn't be more than two or three more posts before he lets you know that. (That's where I got mine). Anyways, if it makes you feel better, you can also get a thermostat, they're relatively cheap.

Tip: If you have to do the water pump and choose to diy, don't get cheap tools!!! They will break if you haven't had to do any other engine work in a while. (Notice the tools stress). Anyways, if you decide to diy and need help, holla at me.

 

Who? Me? I don't sell nothing!
Heck I sell just about everything for repair and upgrade

 

Check for air in the system. That would cause the needle to go hot and then back to normal.

 

after i changed my thermostat thinking it was opned i had no heat. I would drive and occasionally it would overheat, and then drop quickly.
After I found the coolant bleeder bolt and bled the system of air, the heat came back and the overheating went away.

I would think that maybe your water pump is going bad. Warm up the car, then turn it off and have someone restart it while you are squeezing the upper radiator hos. If you dont feel any pressure, then maybe your pump isnt working well.

 

^^^^^
That's a good strategy, I will try that out.. I used a bottle of coolant system sealant a month ago and the leaking problem was not that bad since then. I also think there must be some air pockets in the system but I COULDN"T FIND THE BLEEDING BOLTS ON ENGINE BLOCK, so I just did the radiator and I did bleed the air by opening that bolt on the air intake manifold.

 

Man, your shipping charge is really expensive. Any discount for maxima.org members?

 

Last time when I replaced the thermostat, I didn't have to remove any parts other than the thermostat itself, and the working space was just terribly small. I had to ask my gf to tight some bolts.

 

the shipping is based off of ups's rates.
sometimes it does end up being cheaper because I over estimate weight but usually the shipping is my actual cost.