2005 Sport Trac Temperature gauge drop

[smalltownusa]

My 2005 Sport Trac is running great, with one issue that has me wondering.
Starting down the road I can watch the temp gauge slowly come up to mid range like it should.
However once I turn on my heater fan my temp gauge drops quickly to about 1/4 range.
I'm getting heat (maybe not all that I am supposed to), but I'm not cold in the cabin.

My radiator reservoir was just a little low so I topped that off. I keep checking to see if the fluid might drop thinking I had some kind of bubble in the system, but the reservoir level is holding steady.

It's almost like my thermostat opens, and the temp drops, but never recovers.
With other vehicles I've had thermostats stuck open so the car never heated up, or stuck closed so I overheated.

Any thoughts ?

 

[koda2000]

Check the coolant level in the radiator, not just the reservoir. You may have a leak and a low coolant level. If the coolant level looks okay it may be the t-stat.

 

[smalltownusa]

Thanks Koda I will do that today. I was thinking they are one in the same, but I will check.

 

[koda2000]

Thanks Koda I will do that today. I was thinking they are one in the same, but I will check.

They're one in the same as long as you don't have a leak. When there's a leak the radiator will not draw from the reservoir. Instead it can suck air from the source of the leak. Also, sometimes the hose between the rad and the reservoir can become clogged.

 

[smalltownusa]

Checked the radiator level. I could not put a single drop more in there It's right to the top.
I'm thinking it not be the water pump as I am not over heating.
I could try feeling the top radiator hose to see if it gets warm, but since I have some heat there must be some hot water getting by the thermostat, and it would feel warm anyway.

Sounds like I should try a new thermostat.

 

[koda2000]

Yeah, I'd do the t-stat next.

 

[sr139fox]

Thermostat. Use the correct one. One to cold will keep the engine running in warm up mode or rich until it reaches proper temperature. It will kill gas mileage.

 

[koda2000]

Thermostat. Use the correct one. One to cold will keep the engine running in warm up mode or rich until it reaches proper temperature. It will kill gas mileage.

I got a Motorcraft from O'Reilly's. Most expensive thermostat I've ever bought.

 

[smalltownusa]

Been checking around. Is a 190 Deg. F. the standard factory thermostat? My thermostat is the original.

 

[swshawaii]

OE is 190* (Motorcraft RT-1167) Remember a gasket, sometimes they are included.
http://www.rockauto.com/en/moreinfo.php?pk=511619&cc=1430691&jsn=455

DON'T be tempted to use a "cooler" t-stat. Engine won't run at optimum temperature, and nothing to be gained.
http://www.rockauto.com/en/catalog/....0l+v6,1430691,cooling+system,thermostat,2200
http://www.rockauto.com/en/catalog/.../+thermostat+housing+/+water+outlet+seal,2136

 

[koda2000]

190 degree MOTORCRAFT RT1167 - Typically does not come with the O-ring/gasket. Must be purchased separately.

Get the Motorcraft. Don't cheap out on this part, other brands have been known to not work correctly.

 

[swshawaii]

Also, upper and lower t-stat housing torque spec is 87 inch lbs. (7-8 ft./lbs.)

Many issues caused by over tightening these trouble prone plastic housings.

 

[swshawaii]

Get the Motorcraft. Don't cheap out on this part, other brands have been known to not work correctly.

Painful for me to say, but I installed a Murray 192* thermostat from O'Reilly's. In a pinch, and refusing to go to any of my three local Ford stealership parts departments that price EVERYTHING 30% higher than Ford's MSRP. Murray has been trouble free, appeared to be very high quality, and made in Germany. Generally I avoid house branded parts like the plague, but this may have been a rare exception. No regrets, at least not yet.

 

[koda2000]

Painful for me to say, but I installed a Murray 192* thermostat from O'Reilly's. In a pinch, and refusing to go to any of my three local Ford stealership parts departments that price EVERYTHING 30% higher than Ford's MSRP. Murray has been trouble free, appeared to be very high quality, and made in Germany. Generally I avoid house branded parts like the plague, but this may have been a rare exception. No regrets, at least not yet.

When I originally got my ST the 180K OE t-stat was sometimes sticking in the closed position. I too bought a Murray from O'Reilly's. It worked okay for a couple of months, then it started sticking too. I returned it for credit and bought the Motorcraft. I generally don't buy Motorcraft parts either (because they're sooo overpriced) but sometimes it's worth it (PCV valves, oil filters, spark plugs and plug wires).

 

[smalltownusa]

Thanks for the info. Pricing this thermostat and they are all over the place.
Rock auto has a good price, so I'll order the motorcraft thermostat and gasket from them.

 

[koda2000]

Thanks for the info. Pricing this thermostat and they are all over the place.
Rock auto has a good price, so I'll order the motorcraft thermostat and gasket from them.

Yeah, RockAuto has a good price, then there's shipping and you better hope that the t-stat and gasket are coming out of the same warehouse, or you'll get hit with double shipping. There's a code you can enter to save 5% at checkout. Enter it in the "where did you hear about us" box. The current code is MMEAJ18.