Sorry to bother again, I just changed my head and head gasket on my datsun. The alternator belt is tight, no thermostat, water pump not leaking, the water has a good flow when you accelerate the car and it reaches 3/4 of temp. when only driving around 10 minutes. Do you think my water pump should be changed ? It's about 3 years old.

could be cause you have no thermostat, so water flowing too quick trough radiator to cool down effectively.

I have done this before every time it's summer. I never had a problem. It will stay around 1/4. I always put it on back on fall threw spring so the heater can heat up good in the mornings. But since the alternator froze on me and blew my head gasket, now it's going up pretty quick.

is it the same alternator? maybe is slightly seized and causing drag on the belt, not spinning quick enough.

doubtful on water pup but you never know.

did u get ur radiator checked?sounds like its bummed

Alternator is brand new. Just got it from Pep Boys for only $35.00 leaving my old one. I'm going to take out my radiator tomorrow after work and verify it. Maybe is somewhat clogged :(

This often happens after replacing the head gasket. After warming the engine, the coolant settles from air pockets.
Solution: Let it cool, then top up the radiator.

Another common problem is if the temp sensor is replaced (i.e. head swap). The new sensor may read different from the old. In this case, it is not overheating but reads differently. This is not a problem.

I'm going to inspect all those possibilities and will get back with the aftermath. Thank you all.

Let me be sure I understand.
Your alternator seized, the fan belt broke[?] the water pump no longer pumped & the engine overheated enough to cause head gasket failure.
So far, so good?

Next, you pulled the head & checked it for flatness, & rectified it if it was found to be outside service limits. Then you reassembled the engine with new parts as necessary, then left out the thermostat & you still have problems.

OK, when you cook the engine, the coolant level drops pretty low in the coolant galleries & the scale & crud deposits that have accumulated in there become detached from the metal surfaces as a result of the lumps shrinking as they dry out in the coolant passages that are now high & dry.
These lumps usually fall to the bottom of the block.

Next, you repair the engine & leave out the thermostat, ensuring that the flow of coolant on the block will be high as you take it for a good old test run. This coolant flow picks up the loose crud & sends it round the system at high speed.
Now this stuff is no good & is better off being elsewhere so the car manufacturer installs a very efficient filtration device that will capture most of the solid lumps of crud in the first pass.
We know it as a radiator & it does a good job, but sacrifices itself in the process.

The fix?
Pull the radiator & have it properly cleaned out or re-cored as necessary. Also, give the engine a really good flushing out, including removal of the block drain plug [if fitted] & dig through the crud that is blocking the hole using a thin screwdriver.
Flush, dig & flush until no more crud flows out.

I fitted a coolant filter that looks like a cheesecloth condom into the top hose fitting & was amazed at how much more crud it captured. I removed at after a month the first time & washed it out, then refitted it, then at longer intervals after that until it started to deteriorate.

ALWAYS refit a serviceable thermostat, summer or winter & as long as the cooling system is in good serviceable condition, it will perform as advertised. I have run my stock 1200 coupe at highway speed for hours in temperatures of 100f [37c] & it actually ran just a smidgen cooler at highway speed than it does at town speeds.

Oh yeah, if the hoses are at all suspect, then just renew the bloody lot, heater hoses too. No point in killing a perfectly good car as a result of penny pinching.

Hi Dodgeman, Ok, my car was running fine without the thermostat when heading to the auto show. This is on the highway doing 80 mph. After driving a little over an hour,when almost there, my alt light came on. I pulled over and verified all fuses,fuse links and regulator. The alt was making a weird noise. I decided to turn around because I didn't want to leave late using my head lights and not be able to make it home. So, while driving back I heard a noise like the belt broke, I didn't pull over because my car is automatic and I was only driving with the charge of the battery. About 20 min. from home I noticed my temp going up really fast and the car started smoking around the hood. I kept going because I just wanted to make it home, my car then started pinging and another big bang...I still kept going. I got about 100 yards to my house when the car shut down. I towed it to my garage with my p/u truck and left it there. Next day I took off my head and noticed that the big bang was the rear seal of the head that flew off. The alt belt was gone and the alt was barely moving. I have a A13 head already prepped from the machine shop. I had all the gaskets. I changed all the gaskets and swapped the head. No lubrication on head. Took off head drilled a 45 angle hole and put it all back together. Started car and great lubrication. I bought a new alt and installed it.All the hoses are brand new even the heater ones are brand new. The car never mixed the oil with water. Car never leaked threw the head gasket.All the water galleries were nice and cleaned. So I started the car and let it running for around 1/2 hour in my garage and noticed the temp rising around 1/2. Took off the radiator cap and the water barely runs when idled but when you hit the gas, it will move but not that much. I took it for a spin and around 10 min my gauge was reading 3/4 temp. I went home and touched the radiator and it was hot. I loosened the cap and it was boiling. So I turned it off till today that I took off the radiator. Looks really dirty. So, I'm thinking of taking it to this radiator place so they can swap the 2 lines for 3 for better flow. That's what happened. Never had this problem before. But the car runs much better with this head than the original one.