Thermostat only opens after engine is off -- Why????

[96IsuzuRodeo]

I have a 96 Isuzu Rodeo with 123K miles, 3.2L, 5 speed manual trans.

I cannot seem to figure out why the thermostat will stay closed while driving; however, within 2-3 minutes of shutting the engine off it will begin to open up. Is this normal for this engine as the engine does not overheat. Does anyone have any ideas?

[Ramblin Fever]

How old is your thermostat? If it's the original, get it out, and while you're at it, replace all your coolant hoses, not just the big ones.

Make sure to check the heater/coolant hoses at the firewall passanger side, if they are original, they will fail soon due to age. These two are a BUGGER to change, but don't let them getch you off guard.

[Canucklehead]

Originally Posted by 96IsuzuRodeo

I have a 96 Isuzu Rodeo with 123K miles, 3.2L, 5 speed manual trans.

I cannot seem to figure out why the thermostat will stay closed while driving; however, within 2-3 minutes of shutting the engine off it will begin to open up. Is this normal for this engine as the engine does not overheat. Does anyone have any ideas?

If your Rodeo doesn't overheat then I highly doubt that the thermostat only opens when the engine is off.

[96IsuzuRodeo]

Hi, all the hoses were changed about 1 month ago, same with the thermostat and antifreeze.

It always seems that the lower radiator is cool to the touch.

I am not sure which direction the coolant flows -- weather it is through the thermostat into the lower radiator hose and then out the upper radiator hose or the other way around???

Thank you Ramblin Fever and Canucklehead for your fast replies.

[surferfletch]

Coolant flows into the top of the rad, down through the rad, out the bottom and up to the thermostat housing. Your t-stat remains shut until the temp gets high enough, allowing the engine to warm up faster, then opens. The lower hose should be cooler when the t-stat is open. What's happening with the temp guage when this is all going on? Maybe what you're seeing is normal.

[Canucklehead]

Thermostat Closed


Thermostat Open

[Ramblin Fever]

Sounds normal to me if your driving time is less then say 5-10 miles; I know that I can drive my truck 25 miles/20 minutes or so, and it's just barely getting to operating temperature. I mean the temp gauge will be at norm within a mile or so, but in reality, the truck is just really getting to the temp that it likes to run with at 25 miles.

[96IsuzuRodeo]

Since the engine does not overheat, I guess everything is normal.

The way the coolant circulates through the radiator and engine of the 3.2L is a little different than most vehicles.

Normally the upper radiator hose connects to the thermostat housing. However on the 3.2L engine, the lower radiator hose connects to the thermostat housing.

[Ramblin Fever]

The 3.2L is in itself different then most engines - most have a love/hate relationship for this engine. It's not the easiest to work on, by any means, but it is a very strong/stout engine. Just do not let it get hot or low on oil.