Thermostat Good?

[DIGITRUCK]

Hey,


88 XJ Cherokee Laredo 4.0 Auto. Just got done with the closed to open rad system.

Had a close scare when the temp kept rising (and the coolant in the overflow bottle was bubbling) and wasn't going down even though the dual electric fans kicked in. Turns out I didn't get all the air out and after I did the temp now stays a little over 210 where I'd like it to be.

Here's my prob, when the engine is cold the top rad hose is soft. After about 10-15min the rad hose gets hot and really hard. The fans kick in and after awhile this top rad hose gets a little softer but not much. Then I can see the temp guage drop from 210+ to around 180+ (but I'm not sure if it's accurate after all the vehicle is an 88). I know this means the THERMOSTAT opened but is this normal cause the top rad hose is only a little softer and not rock hard. Could it be it only opened partially? Can they even open partially?

Please let me know whether I need to change this Thermostat or not.

btw - It was changed last year around this time. It's a 195 deg model.

Thx, Phil

[GregA]

... Just got done with the closed to open rad system. ...Had a close scare ... Turns out I didn't get all the air out and after I did the temp now stays a little over 210 where I'd like it to be.

Yep - works much better once the air is out of the system.

My '92 was similar before I had the (original) radiator replaced last summer. The ORIGINAL radiator was really thin and didn't have a whole lot of cooling capacity. The replacement was thicker & works much better. Now the temp sits below 210 almost all the time. Thermostat is new 195 degree.

Here's my prob, when the engine is cold the top rad hose is soft. After about 10-15min the rad hose gets hot and really hard. The fans kick in and after awhile this top rad hose gets a little softer but not much. Then I can see the temp guage drop from 210+ to around 180+ (but I'm not sure if it's accurate after all the vehicle is an 88). I know this means the THERMOSTAT opened but is this normal cause the top rad hose is only a little softer and not rock hard. Could it be it only opened partially? Can they even open partially?

Please let me know whether I need to change this Thermostat or not.

btw - It was changed last year around this time. It's a 195 deg model.

Thx, Phil

Sounds "normal" to me.
When cold, there is NO PRESSURE in the system. Once HOT, there should be about 12-15 lbs of pressure. This should stay that way until the system cools down again.

Yes - thermostats can be partially open.

Just for fun (or call it a "Science Experiment"), get another thermostat and put it in a pot of water on the stove. Start with cold water and bring it to a boil (212 degrees) and watch what happens to the thermostat. Then let the water cool again (or mix some cold in) and watch what happens.

Take Care,