Need a little help.....

[bennettmotorsports]

I bought a 2003 Neon with a broken timing belt. I replaced the timing belt, water pump and got a head from a known good Neon. I had the head shaved. Installed new head gasket and bolts and all the gaskets, o-rings and such on the top end of the motor. The car started and runs fine. I drove it a bit not long distances though. I sold the car to my brother in law. it has a fresh oil change, fresh plugs and wires. It was flushed with the Prestone flush and refilled with new 50-50.

He is having a few issues. Which I feel obligated to help him with

1. It was over heating after driving about 20-30 miles. He bought a new radiator from the parts store and installed it. It has a new thermostat and radiator cap. The car ran fine he in did a few 100+ mile trips and no issues. Now after about 3 weeks of not over heating it started again yesterday. He drove it about 30 miles and it sat for about 1.5 hours. I didn't not over heat that time. He started on his way home and got 5 miles down the road and it overheated.

2. Also yesterday for the first time. He was sitting at a stop light before it overheated and the oil light came on. He pulled over into a gas station and checked the oil. It read fine on the dipstick. It was not milky or looked like antifreeze was in the oil. So he continued down the road. Then it did it again at the next stop light. Then shortly after it overheated.

3. CEL is on I have scanned it. I don't remember the code off hand but it says the upstream o2 sensor. When I bought the car from the people I noticed it had a brand new o2 sensor on it. My brother in law bought a new o2 sensor and the light went away for a few days and is back on. Both of the o2 sensors were Bosch sensors from like Advance or whatever.

[Danteneon]

Start with the basics. Check the coolant level. Is it low? That can cause the car to overheat. If it's low, find out why it is. You might have some air in the system. Is the radiator fan working? That would cause the car to overheat in town but not at highway speeds. Is the t/stat stuck shut? Etc.

[occasional demons]

The type of code for the o2 sensor matters too. Is it lean? is it shorting out? etc, etc.

If for some reason it is running too lean, it may overheat, not to mention damage the pistons, valves or the head.

Depending on the code, the o2 may be fine, just doing it's job.

If the t'stat you used has no bleed hole, (Jiggler valve) it can very well have air trapped in the system. Even with the valve, you need to fill the system slowly, to let the air escape. Otherwise it will appear full when it is not.

[titansxt]

How is the idle on the car? Does it dip real low to the point of the oil light kicking on? Maybe the tensioner is not giving the right amount of tension and causing the water pump / oil pump to pump inefficiently.

I know that the O2 code came up a bunch when I was having fuel pump issues. I would worry about that the least right now.

[occasional demons]

The oil pump is driven directly off the crankshaft. If the water pump was slipping, due to not enough tension on the belt, the valves would likely be toast by now.

Hopefully the impeller is still intact on the water pump, as it was recently replaced.
How about the radiator hoses? Are they new, or the original ones?

The heater hoses? Are they good? If one is collapsed, or the heater core is clogged, it will not circulate coolant in the engine when the t'stat is shut. By the time it opens, it may be already overheating. It is nearly impossible to loop the heater hose at the tubes without kinking it unless you get more than a few feet to loop it. This would be a check for the heater core flow. If it no longer overheats with the heater tubes looped, then it is the heater core.

Of course there is always the possibility the heater tube is corroded shut... I have seen some for sale on ebay that looked pretty bad inside. The cooling system would have to been really neglected I would think, for that to happen.
Edit:
You can bypass the heater tubes/core by running a hose from the nipple in the head to the nipple in the water pump inlet. Just be careful removing the hose from the WP inlet. That nipple breaks easily...

[titansxt]

The oil pump is driven directly off the crankshaft. If the water pump was slipping, due to not enough tension on the belt, the valves would likely be toast by now.

Eh. Just throwing ideas out, its all interconnected.

[bennettmotorsports]

Here is what I know.....

The fans do kick on. It started to overheat at 60mph. The thermostat is the $8 one from O-Reilly's I know it has the little copper jiggly part. The radiator hoses are still original. The system is full of coolant. I did not see any collapsed hoses. The heat does work.

It idles rough sometimes. But it was not when the oil light came on.

[occasional demons]

One thing I forgot; radiator cap:

If it isn't holding pressure, it will boil over. It may not recover coolant from the overflow tank either.

You may want to check the level at the cap when cold to be sure it is full.

If the hose is collapsed internally, you won't see it.

[titansxt]

Grab a pot of water and boil the thermostat. See if it pops or not.

[fattycrack]

bosh o2 sensors are known for reading weird, if i remember correctly the resistance is different so the reading is different and after a few miles and braking them in the reading is off even more. this could be the reason ur getting this code. try using a different brand, id use the dealer recomended one. and for the over heating, ive had this same problem and ive just had to replace the thermostat a few times. sometimes those come broken right outta box.

[g_force58]

If you haven't got this fixed yet, did you check that the jiggler is positioned at the top when installing the thermostat? IIRC it should be installed with the jiggler in the 1 o'clock position when inserted in the head. This allows trapped air to bleed from the system.