Sunday, May 3, 2009

How To Change a Thermostat on a V6 Ford Ranger

A car's thermostat controls the flow of coolant to keep the engine in its prime operating temperature. Thermostats can become stuck in either the open or closed position. In either case, it will need to be replaced.

I noticed the temperature gauge needle never got off the very bottom mark unless I drove on the interstate for over 20 minutes. Even then, it barely got above the cold mark. I knew either the thermostat or the temperature sending unit were bad. Since I was flushing my cooling system, I decided to go ahead and replace the thermostat to see if it would fix my problem. Thermostats are inexpensive (around $5), so well worth the price to "throw parts" at a problem to see if the problem can be fixed.

Troubleshooting the Thermostat
A working thermostat will let the engine get into its normal operating temperature within a few minutes of running and keep it there. You will also be able to get heat from the HVAC controls relatively quickly. If your car has a problem with any of these, the thermostat may need to be changed.

The thermostat may be stuck open if...
  • The engine takes a long time to heat up - indicated by either the temperature gauge not wanting to leave the "C" or "Cold" mark. (Check to make sure the Temperature Sending Unit is working properly, as this may cause an incorrect temperature gauge reading).
  • It takes a long time to get heat from the HVAC.
  • The upper radiator hose never gets hot, even after the vehicle has been driven for several miles.
The thermostat may be stuck closed if...
  • The engine overheats after a consistant amount of time driving, shortly after starting the engine and no leakage can be found from the radiator, hoses, head gasket, or heater core.

Tools and Materials
  • 10mm socket (1/4" drive)
  • 1/4" ratchet (there is not enough clearance for a 3/8" ratchet)
  • Small 1/4" extension
  • 10mm combination box-end and open-end wrench
  • New thermostat with gasket
  • 50/50 mix of coolant and water to top off the radiator if any spills out during operation

Changing the Thermostat
A good time to change the thermostat is when the cooling system is empty, like during a coolant system flush. It is possible to change the thermostat with a full cooling system but some coolant will leak out of the disconnected hoses.

Follow these photos and captions for the thermostat changing instructions on a 1996 4.0L Ford Ranger:

Locate the thermostat housing by following the upper radiator hose to where it connects with the engine block.


Here you can see the thermostat housing tucked away.


You will have an easier time accessing the thermostat by removing the throttle cable splash shield and disconnecting the electrical connector that goes into the air intake. You can also completely remove the air intake hose, but I opted not to.


You will need to remove these two 10mm bolts.


And there is one more underneath.


Here is the thermostat (red arrow). The blue arrow shows the Temperature Sending Unit which controls the temperature gauge. The TSU will always have one wire coming out of it. The green arrow shows the Temperature Sensor, this sensor tells the car's computer how hot the coolant is. This sensor will always have two or three wires coming out of it.


Remove any old gasket material from the hose side and engine side of the thermostat housing.


Here is the new thermostat with rubber gasket installed. Note how it is installed. The spring side should go towards the engine.

To finish: follow the steps in reverse.

Before it took a lot of driving to even move the temperature gauge needle on my truck, now the truck warms up quickly and stays in the normal temperature range like it should. This should help keep the engine running well, improve gas mileage, and keep emissions low.

11 comments:

Anonymous said...

Thank you for your blog. It was helpful to my husband in knowing which way to install the thermostat.

Capri said...

Hey man, random comment from a perfect stranger:

Thank you so much for your diagram. I've never even changed a battery, but because necessity called, I had to change my thermostat.

After two frustrating tries, I went to the internet for some sort of diagram. Yours was hands-down the best, and it gave me the confidence I needed to tear into my 95 Ford F-150.

Thanks so much man.

Matt said...

Fantastic post, thanks for the help.
The photos are very well done and helpful!

Anonymous said...

Awesome post! Very helpful! Thanks

Mark said...

Great directions for a nonmechanic. Thank you!

HERBERT said...

To bad our government is'nt as transparent as your instructions.This was off the hook good.

Chevy HHR cold air intake said...

Perfectly done. I can't help envying your work.

Air Intake Kits said...

Your post proved to be very helpful to a lot of readers and amateur enthusiasts. Thanks!

Anonymous said...

really awsome so detailed and easy to understand im changing mine in the morning now i know how to get it done thank you a millllllllllllion!!!!!!!!!!!!!!

Hardy said...

Nice! Easy fix. Like the pictures.

Anonymous said...

Joe said...
Five years after your post, it is still the most helpful illustration on the web for changing a thermostat- particularly on a '90s Ford. It saved this amateur mechanic a lot of guessing, fumbling & wondering again today! Many thanks for taking your time to help total strangers.