Check engine light turned, heater not working properly

JAMI NELSON

MEMBER
2002 MERCURY MARINER
4.6L
V8
2WD
AUTOMATIC
100,000 MILES

I have the car listed above LS model that just clicked over 100,000 miles and a check engine light came on right after and also noticed the heat wasn't working that great (29 outside at the time). So I pull over and pop the hood and the car should be hot by now I mean I have driven 30+ miles and let it warm up a good 10-15 minutes before I left, but I was able to rest my hand on valve cover and check fluids and no burn or scalded hand. I checked the hose for pressure and was a little bit but not what it should be so I pop the coolant tank and no hissssss. Now there was coolant in it but it didn't look the greatest I mean it could be a mix of different coolants (just got the car few months ago and father in law not a car guy) so I baby her home and I am pretty well rounded under the hood and all but I figured pick someone's brain for maybe a tip or idea on what it could be before I go freeze out on the garage floor so I can play in some grease. The car has been garage kept grocery getter basically. Any tips will help. Thanks guys. -James (The Chevrolet guy loving his Ford) shhhh. Don't tell my dad. Haha

2 Replies

STEVE W.

MECHANIC
13,452 POSTS

Well, the first thing I would do is scan it for codes, with your description I would expect a P0128. That is a code meaning the thermostat isn't working correctly and the engine isn't heating up. The easy solution is to drain the cooling system and replace the thermostat. As you have questionable coolant I would probably do a drain and flush just to get whatever is in there out, then install the new thermostat. On that engine you just remove the engine cover, then drain the coolant down and remove the two bolts, then lift off the thermostat housing and pull out the thermostat. Clean up the surfaces and install the new thermostat and gasket and tighten it back down. It uses plain green coolant or you can use the gold, which is still conventional coolant but more $$. Total capacity is close to 5 gallons. Make sure you get the correct thermostat as that car uses a bypass that gets closed as the thermostat opens. Ford # 7L3Z-8575-B
The code should clear itself once the thermostat works properly or you can clear it.

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