When I got home I notice my car started to overheat. In coolant reservoir there was boiling coolant when I opened up the hood. Today, I started my car and rev up to 3k to warm it up a little and wanted to see if my fan kicked in, but no luck either. I notice that the top rad hose was hot, but the bottom stay pretty cool. Is the cause of a thermal stat staying open?

 

Thermostats are inexpensive and easy to replace, it can't hurt to replace it if it is more then a few years old anyway, even if it is not the problem.

A thermostat stuck open generally does not lead to overheating, one that is stuck closed would.

The rad fan will turn on when engine temp. reaches just under 200 degrees F, about 1/2 way+/- on your temp. gauge.

With engine cold, remove rad cap and start engine, check for any bubbling, [boiling] in the rad, any air bubbles in the rad indicate a blown HG, it can also show up in the overflow reservoir once engine temp is up and thermostat opens all the way and pressure in rad increases past rad cap limit, "In coolant reservoir there was boiling coolant". 94

 

thanks for the fast reply, I will replace the thermalstat, because I;m pretty sure it hadn't been replace so far. When I started my car i did notice a bubble here and there when i squeezed the hose. I will let you know how it goes.

 

If you are getting bubbles when squeezing hoses, that would indicate air in the coolant system, which can result in over heating and "boiling" in the reservoir.

Because you have to anyway, once you replace the thermostate, make sure you bleed the coolant system properly.

Depending on MM&Y of car, you may have a bleed valve on the thermostat housing. 94

 

alright, the car is fixed. I replaced the thermal stat and everything working fine. The old one look pretty beat up and burnt inside.