Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

2004 Ford Mustang GT serpentine belt diagram

After replacing the water pump, thermostat and new serpentine belt 2004 Ford Mustang GT still over heating. Could the belt be on so the water pump turns in wrong direction? I ask because I removed all hoses and pulled the thermostat, then ran water through the engine. While car was off water ran through engine and out through bottom. When I turned the car on the water started back flushing out the top of engine with VERY little coming out bottom. If this is the problem could you provide the correct serpentine belt diagram? Mine goes starting from alternater over alt., down and over power steering, under crank, under A/C compressor pump, around water pump, under the tentioner, around smog pump and ending back at alternator.

Here is the drive belt schematics. You may have to register at the site to see the information.

Isn’t there a belt routing map under the hood?


The coolant is supposed to come out the top radiator hose, through the thermostat as the engine, as the engine runs. With the engine off, the coolant (water) will gavaty feed out the bottom hose. It’s normal.
Your problem is engine overheating. You should make sure, with the bottom hose off (and engine off), that water will go through the radiator and out the bottom.
A leaking head gasket could be causing the engine to overheat. A coolant system pressure test will reveal internal/external leaks.

Thank you, I was already a member so I can look at it. This is exactly how I have mine configured, so that elimates the belt being wrong. Now if I could figure out why it is still overheating. So far eliminated water pump, replaced it, eliminated the thermostat, replaced it. Now eliminated the serpentine belt configuration, your assistance shows mine is set up correct. I did a complete engine flush and found no issues there, so the only thing I can think of now is the possibility that the electric fan is not operating correctly, it does come on because I saw it running maybe it is not turning at the correct RPM or staying on long enough?

I see no water in the oil and the car does not smoke, at all let alone white smoke. I don’t have the equipment to do a pressure test so I suppose I’ll take it in and get it checked. This whole thing started when my wife was driving home from the store, she first noted it making a desieling noise and then she said it suddenly stopped running. I went to her and it had cooled enough to start, the temperature gauge was regestering in the normal range and no noise. So I started driving it the rest of the way home. I got a mile when suddenly it started making the noise described and the temperature guage went from normal right off the scale to overheated and the engine quit. I let it sit for about an hour and a half and drove it the rest of the way home without any issues or noise. I replaced the water pump because I noticed water around the relief hole. While at it I went ahead and replaced the thermostat with a 180 degree unit and put on a new serpentine belt, the old one was cracked so why wait for it to break? Did an oil change and changed out the spark plugs just so I had a record of when they were last done. Started the car drove it same distance as it was driven when the problem first occured with no problems. Figured all was well, so the next day drove it again, let distance this time and noticed the gauge starting to climb. Shut the car off awhile then drove it back home and guess what it overheated and died in the driveway. This is what lead me to start looking at the belt diagram and doing an engine flush. I was thinking I should have the electric fan checked to ensure it is not the problem. Never considered a blown head gasket because when I blew the head gasket in my 1994 3.8L Mustang it started running really rough, blew white smoke out the exhaust, and stalled out.

Head gasket failures on 4.6 l modular motors are uncommon. If they have been abused, however, it is possible. You probably have a two-speed fan with this car. Does it work at both speeds, low and high? Why pressure test it, were you losing coolant? You can often sign out pressure testers at auto parts stores in their tool-loan programs.

You wrote something that indicates this car is new to you. Do you have an owner manual for this car? You should get one and read it if you don?t. Look up the part about fail-safe cooling. Unless I missed my guess, you have it. It operates like this on my Merc according to my manual: If the engine gets too hot (cyl head temp sensor) the temp gauge goes to full scale and the PCM systematically shuts off the injectors on half the cylinders. (I believe it rotates the shutdown rather than pick half of them continuously.) You will have no AC. You are not supposed to drive like this unless it is absolutely necessary. If the engine gets too hot, it will shut down.

I suppose a flakey CHT sensor could cause these problems even if you are not overheated. You may have a coolant temp sensor and an CHT sensor. I think that he coolant temp sensor will normally run the gauge, but the PCM overrides it if the CHT says it is overheating. If you don?t have an owner manual, look to download one at or

Additional advice: put the t-stat in that is required if you changed to a cooler one. If the one you have is too cool will prevent you from going into closed-loop operation and turn on the CEL. You will also have less power and consume more fuel. You should run Motorcraft or Autolite plugs. Others may give you problems. What kind of coolant did you put in? You should be using G05 ( You can find the Zerex product at NAPA for one place. It is a lot more costly at the Ford Dealer.

Good luck.

Thanks for all of the great information. I am loosing coolant because it appears to be back flushing into the closed unit tank and once it fillsto capacity it starts coming out around the fill cap. I bought my replacement plugs and thermostat from the Ford dealership and they recommended an Itainium plug, said it would help with performance and fuel economy. They said the 180 thermostat would allow me to get heat in the car sooner in the winter and cool the engine sooner in the summer. All these things made sense to me so I went with their recommendation, besides they work for Ford so I figure they had the inside scoop for the local desert area we just moved to. I am running a 50/50 coolant and although I understand what and why you say to run Zerex, this problem started before doing anything at all to the car. As I mentioned above it came on very suddenly, my wife was driving home from the store (she is a VERY concervative driver). She stopped at a red light and started hearing a noise (the best I can describe it is a desieling sound) and at almost the same time the engine shut itself off. After it cooled down it started again so I started driving it the remainder of the way home and it did the same thing, it started making the noise and the temperature guage suddenly went from normal range to off the scale HOT and the engine shut down. I let it sit for two hours and drove it the rest of the way home.

Yesterday I started it and let it run until the temperature started into the normal range. I then went into the engine compartment and began watching to see if I could find the cause. To my amasement I saw the coolant backflowing into the tank and then out around the filler cap. The first time it did this when my wife had the problem I thought whoever topped off the coolant for her forgot to tighten the cap back down but when I saw it happen first hand I now firmly believe the problem stems from something in that general area.

“To my amasement I saw the coolant backflowing into the tank and then out around the filler cap.”

This is expected. If the coolant in the engine starts to boil the pressure will reach the limit of the radiator cap. Then the coolant can expand into the reservoir enough to overfill it.

I second the recommendation to go back to the standard temperature thermostat. It’s a common misconception that a cool thermostat will help an overheating problem. Both thermostats will be wide open when the engine is overheated.

It’s possible for a head gasket breach to only allow combustion gasses into the coolant, like a one way street. This will not generate exhaust smoke or steam. Try revving the engine with the radiator cap off (take the cap off when the engine is cold). If you get bubbles in the coolant that smell like exhaust then it’s the gasket.

With the cap off and the engine fully warmed up you should see coolant flow strongly by the radiator neck when you rev it. If a lot spurts out the cap it’s probably a clogged radiator. WEAR GOGGLES.

Thanks, will try that. Like you mentioned earlier it is a closed system so there is no radiator cap and when I did a complete engine flush of the engine I don’t really recall smelling anything unusual (just the smell of coolant) but at this point I am willing to try anything!! I did put the old thermostat back in the car this morning but still had the same results, just went ahead and left it in since your previous recommendation.

" I removed all hoses and pulled the thermostat, then ran water through the engine"

Where & how did you run the water in? Where do you fill the system? Sorry I’m no Ford expert.

Is the fan running full speed when it overheats?

I pulled all hoses off and removed the thermostat, I took a garden hose and put the water in through the the thermostat housing with the engine off. The water flowed out the bottom great force, I kept it running through the opening until I saw all the coolant was gone and clear water came out of the bottom opening. I then started the car with the water still flowing into the thermostat housing. As it started warming up the water started flowing back out through the thermostat housing, it did change to white foaming water as it came back out. Not as much as one would expect but I figured that was because I was forcing water in from the wrong direction.

After running the water through the engine I moved the hose to the top inlet opening on the radiator and flushed it. The water shot out of the bottom opening with full force and I ran it through the radiator until all of the coolant was gone and clear water was coming out.

As for the fan: When the carf overheated yesterday the fan never came on. On previous instances it did run but I couldn’t tell you if it was slow or fast.

You were doing what’s called back-flushing. The water pump is supposed to pump coolant out of the thermostat housing. Someone else can correct me, but I don’t think you’re supposed to run the motor when you back-flush. What you should have done after flushing is put the hoses back on and fill the system before starting the engine.

The fan not running when it’s overheated is a definite issue. Get it to overheat and carefully check the bottom radiator hose to see if it’s hot. If not there’s a flow problem. If hot coolant is flowing through the radiator, and the fan doesn’t run this is at least part of the problem.

You might force the fan to run by turning on the A/C. Disconnect the A/C compressor clutch wire to do this without adding heat to the radiator.

I’ll try that and see what happens. I didn’t run the engine for more than a minute or two and althoug I was doing a back flush I was still getting water out of the bottom opening so I don’t think it caused any harm.

I too have been concerned about the fan and I tried to find what the output voltage is supposed to be so I can verify that is correct, but finding anything on this car on the net has been a real pain. I bought a Haynes repair manual but it hasn’t been any help. I have a Chilton’s but so far everything it suggests I’ve already tried.

“I don’t think it caused any harm”

I didn’t mean to imply it was harmful. Just messy, not what’s normally done.

For about $7, I’d put a new radiator cap on it…just to be sure that the old radiator cap isn’t the problem.

Doesn’t have a radiator cap.

Overheating 4.6L Ford Mustang GT 2004. I’ve changed the waterpump, the thermostat, then flushed the engine and back flushed the engine, got good water flow both directions, flushed the radiator with good water flow, checked for water in the oil (none), and checked for white smoke out the exhaust (none). Took it to a local shop for Diags and they state it passes the block test. Have no check engine light so no codes to check. Replaced spark plug, scheduled change, and found no water or unusual issues. Changed the oil, was also due for scheduled change, no water, no sediment,and nothing unusual in the oil. When engine is cold ALL anti-freeze out of holding tank, shortly after startup tank fills and at normal temperater range it is at capacity. Shortly (about two to three minutes temperature guage goes off the scale past hot and the engine dies. The car can not be started again until cooled off. When I drained the coolant I noted only a little drained out, about a quart drained out, I then started the car and it fills the holding tank to overflowing again. When I hold the return radiator hose I feel water flowing through it. I am stumped!!

Read carefully. The fail-safe cooling feature kicks in when the CHT sensor sees a temp too high. At that point, the temp gauge does not indicate coolant temp any more, it pegs. At this point, the engine will alternately disable injectors to cool the engine. It will run on half its cylinders. If the CHT sensor sees a temp too high, it shuts off the engine. All of this could be caused by a faulty CHT sensor. I don’t know if it would trigger a code or not. I feel that the “dieseling” you wrote of might be cylinder deactivation.

I took the car to a local repair shop and asked them to run a diagnostics to help determine what the real problem is. They ran a block test which concluded the engine had no problem, then while getting a printout of the test results the car overheated and shut itself off. And of course it would not start again until it cooled. So my question to you is if the CHT sensor or sensors are faulty why didn’t the block test pick it up? Is there a way to test the CHT sensors? If so how?
By the way I really appreciate all of the assistance and information you have provided, even though it has not yet resulted in me fixing this issue, it has helped me eliminate the local mechanics here who only tell me I must have a cracked cylinder head and they will re-build the engine for me. I can and will do that but only as a last resort and only after eliminating all other possibilities.