thermostat question

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Sep 20, 2012 | 07:05 PM

Jose A.

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Fleet Mechanic

Joined: Apr 2003

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From: Florida

thermostat question

all of a sudden, and when driving, my '97 4.0 Aerostar Temp Gauge goes to maximum (to the right extreme of the temp gauge), and as soon as it gets there, it starts coming back left to below Normal, and then it does it again, and again. Up and down, up and down.

I previously replaced the Coolant Temp Sensor with a Ford replacement sensor.
Temperature has been fine until the last 7 days when it has been doing this.

is my thermostat just sticking closed?

if yes, which is the best thermostat to get? (I want a thermostat that opens earlier instead of later).

this is one part I do not want to go cheep cheep.

Thanks for tips.

Sep 20, 2012 | 08:18 PM

Muffinman

Laughing Gas

Joined: Jun 2004

Posts: 1,240

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From: Dallas, Texas

Sounds like the thermostat is bad, unless you have a big air pocket in the system.

I use Ford OEM for that part. it last another 15 years. The price is $22.00 last one cost me.

You choose a thermostat based on climate. If the weather is normal 60 degrees of more all year round get the 185, If it gets cold for 4 or 5 months you get the 190, 195 ones. This lets the car reach normal operating temps for best performance.

Sep 21, 2012 | 04:26 AM

Jose A.

Thread Starter

Fleet Mechanic

Joined: Apr 2003

Posts: 1,460

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From: Florida

thank you, the 185 thermostat it is, since Florida is as hot as Texas.

Sep 21, 2012 | 05:41 AM

xlt4wd90

Lead Driver

Joined: Sep 2003

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From: SoCal

The engine computer needs to see at least 192F in order to work properly, so you should not get one rated below that. If you have an insufficient cooling system, the thermostat is not going to help. If it has to open full up trying to maintain its rated temperature, it is entirely up to the radiator and fan to keep the engine cool.

Sep 21, 2012 | 01:59 PM

96_4wdr

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Joined: Apr 2005

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From: Washington state

with PCM electronic controlled engines, the thermostat temp. is spec'd for the PCM programming for correct fuel burn.

Motorcraft is the best but hard to find, then the Premium Stant stainless steel. the manuf. lists and spec's for your engine/rig

too cold a thermostat will cause crankcase engine oil contamination, too hot a T. will cause preignition

Sep 21, 2012 | 10:05 PM

Muffinman

Laughing Gas

Joined: Jun 2004

Posts: 1,240

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From: Dallas, Texas

Quote:

Originally Posted by xlt4wd90

On the Aerostar it has 2 sensors. One for engine side temp and the other for coolant side temp. The PCM see these Two temps and makes the adjustments based on those.

I never seen a 185 miss behave yet in Texas for running it. I still get 25 MPG highway at 60 MPH and I get the steady in the middle Temp gauge reading. That is with the AC blowing the whole time, Which makes a big difference here. It hits 105 degree days here for 3 months, average is around 92 degrees for 9 months.

Sep 22, 2012 | 08:59 AM

Jose A.

Thread Starter

Fleet Mechanic

Joined: Apr 2003

Posts: 1,460

Likes: 6

From: Florida

seems to be the same principle for Jaguars, there are two thermostats, one for northern climates and one for southern climates. (one opens later, one opens sooner).

my van was originally sold in Florida, (southern climate), I'm wondering if the thermostat was replaced with a 192 degree stat. But this symptom just started happening, it was working fine, Temp staying around Normal no matter the traffic or outside temp.

I'm inclined to check for an air bubble since I did have to add coolant recently.
if that is not the problem, then it's the thermostat gone berserk.