Originally Posted by mikesimpalass

Hi guys, my car is starting to have an overheating problem that I'm having trouble diagnosing. It is an ls swapped gbody monte carlo. Up until now, my car never had a problem cooling. At idle, the temp would climb up to around 205-210, my electric fans would kick on, and the temp would drop right back down. But now, at idle, the temp climbs up to 225 with no sign of stopping, and then I just shut the car off.

I have a massive 4 row copper brass radiator. The previous owners of my car had it custom made and I inherited it with the car. It previously cooled a 600 horse iron headed big block WITHOUT a fan shroud.

I have bled the system for air a few times with no avail, I have front and rear steam vents that I've opened up and bled coolant out of.

My Taurus fans are running, and I've confirmed that they are freely flowing air through the radiator.

I replaced my thermostat and it did not make a difference.

Here are a few observations I've made. *while the engine is starting to overheat* , my upper radiator hose is hot, while my lower hose is pretty cool......and, when my engine temp climbs up close to 220, if I Rev the engine to around 2500 rpm, the engine cools down very quickly to 205.....

This makes me believe that either my waterpump is on its way out, it's a relatively new ls3 water pump with just a few hundred miles on it, or my radiator is clogged up. Any advice on how I can diagnose my problem going forward?

As always, thank you!

Originally Posted by LS6427

Water pumps never stop pumping water/coolant......unless the shaft is sheared. They spring leaks in their seals, thats why we have to replace them. But if it was sheared then you would overheat immediately, every time.

Take the t-stat out and bolt the housing back up.....see if both radiator hoses get hot. If they do, then there's no obstruction. Obstructions and clogged radiators is almost an impossible thing, unless you drop a rag into the radiator.

I would guess you purchased a bad "new" t-stat....and the old t-stat was the problem.

But first check for flow the way I described.......

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