Hi,
My 1999 Ford Expedition recently stopped blowing out any heat. Blower blows fine, but not enough heat. Brought it to a local shop and they replaced the thermostat. Picked up the truck and bearly any heat and truck runs rough. Check engine light came on half way home. Brought it right back to shop and they said that it takes the thermostat awhile to "open" up and that I probably need new spark plugs. Truck ran smoothly when I brought it in. Spark plugs were changed at approx. 90,000 miles. Could the shop have disrupted anything or caused the truck to misfire and engine light to come on. Computer check said something about cylinder #7 misfire, but something seems weird. Please advise.

Hey - the thermostat opens when the engine is up to the prescribed temp to cool the engine. Heat is available before the engine is at full temp. If temp gauge reads in normal range heat should be available. If thermostat was stuck wide open the engine would run cold and so would you

I believe this engine has a few vacuum elbows that are not so tough when original they were failing fairly soon. That could explain a lot and would explain it running poorly and the check engine light. The ones I ran into on this vehicle were hard to get at and two were on passenger's side of the engine - one toward the firewall was hard to even put your hand on.

Vacuum leaks can effect all kinds of controls including the heating/cooling ducts of the heat/A/C for the vehicle. The leaks will fool computer into making wrong engine control adjustments and alone just let air in without mixing in fuel. Check for noise of a vacuum leak and bet that is the problem now and was then but is worse now,

T
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Tom Greenleaf - MetroWest, Boston
http://acsource.net/acforum/index.php

Brought the truck back to the shop and now they are saying "yeah, it's the heater core. You're getting heat in the rear and it's gonna take us at least 6 hours to fix it". What the?? Why didn't they tell me that before. First it was the thermostat needs to open up, takes a couple of times. Now it's the heater core without even looking at it today.
I had a small amount of heat before the thermostat was replaced, only on the first and second setting. Still the same amount now. Blower still works fine. Air-cond. works great. No smells. No obvious leaking in the truck or on the ground. Hose to radiator is warm.
Engine light is still on. When I asked about changing to a different cyclinder and then checking the computer diagnostics, they said "oh, yeah, well, uh, yeah, I guess we could do that".
What's next? Told them I would call them later.

AGAIN - the thermostat stays shut till it reaches about 195F. You can see the needle go up and stop at that point on your gauge. If it didn't open you'd overheat - period. There is heat at 160-170-180-F available and gets warmer as the engine warms up. Duh! Does your temp gauge show the engine warming up and stabilizing? Probably yes.

It the heater cores are not leaking they may be plugged up. That you would flush them out first before replacing them.

AGAIN - You said it went in for poor heat and came out with a rough running engine and still no heat. Those vacuum elbows are like about 3 inches long if straightened out and about 10mm I.D.

The heated coolant may be controlled by a vacuum operated valve for either or both of front and rear. If no vacuum is available because of a leak they wouldn't work and engine wouldn't run well. Any time engine runs rough it will set off a code and check engine light. These elbows - the one toward firewall on passenger's side somehow get real soft and just touching them is enough to end it for them.

Ok: You may have needed the thermostat to start with - don't know that either right now. You left with a problem that could explain what's happening now. This vehicle also needs like any to get all air out of cooling system or it will be erratic and it had to be drained or lowered to do a thermostat. That must be known full at the pressure cap some at radiator and some are on the recovery tank - don't know for this one for sure. If it was left low on coolant it would drive fine for a while and would overheat!

System needs to be known full of coolant and run at a steady temp. You can feel heater hoses and see if they are warm or not or if they stop being warm at a heater control in them. Heater hoses are about the size of garden hoses - usually 5/8 for inlet and 3/4 for outlet.

This thing doesn't work as well as when you started. Them telling you the thermostat needs to open just isn't the up front issue right now. If they suspect plugged heater core(s) you should take hoses off to them and force/flush water thru them forward and backwards. If it can't let water thru they could be plugged up but most would flush out junk and behave again. When they leak they need fixing or replacing.

Something is all confused about this problem and the fix. Ha - could be the way I'm reading it. Right now I need to know if the engine warms up normally and stays there. Listen for the vacuum leak(s) -- I'm close to sure that's the rest of the trouble with misfiring and check engine light. Left too long like that it can mess up your cat/converters so get help elsewhere if this place can't figure this out,

T
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Tom Greenleaf - MetroWest, Boston
http://acsource.net/acforum/index.php

Tom, thanks for the speedy replay. I can see where you are alittle confused, so am I as I know nearly nothing about cars (that's why I'm here )

Anyhow, yes the engine warms up normally and stays stablized. No problems overheating, etc.

Ok: I think you need another shop. Print this out if you want if you think it may help. I really don't think this is a high tech problem. Just tell a new place the story so far and let them fix this. If it is in fact the vacuum elbows they may be dealer only or can be faked at least temporarily by making a loop-d-loo out of 10mm fuel line. If that straightens the whole thing out then do take this on a good highway run to burn out some junk that the misfiring has probably already caused.

Good luck with it. Try a tech with some gray hair may help

T
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Tom Greenleaf - MetroWest, Boston
http://acsource.net/acforum/index.php

Hi Tom,
Thank you so much. I'll let you know how things work out at a different shop!