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Daily Driver since 2/03
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995 Posts
Discussion Starter #1
I went to work Thursday, all was normal. When going home (50 degree evening) I turned on the heater and noticed it was only lukewarm. The donor temp guage was on the next to bottom mark, way below normal. I thought the thermostat was stuck open. I tried downshifting and running with the rpms up around 3K but it didn't help. Over the weekend I replace the thermostat with a 195 degree one. The old one was also 195 degree and was not stuck open. It seemed to be operational. With the new thermostat in, it still runs cold. The temp gauge will go up to almost normal if I sit idling for several minutes but at soon as the revs go up, the temp goes down. Next I thought it might be a ground issue for the guage but that doesn't explain the heater not working like it used to.

Is there some kind of check valve or by-pass-in-case-of-clog that I should check? I've googled a couple of similar complaints but nothing showed a resolution. I was hoping someone might have a suggestion here. My next thought is to flush the system and see if something is clogged up.

In case it matters, it's the 354HP crate engine from the ford catalog with stock EFI, smog equipment, cats, FFR heater option, stock radiator, thermal switch controlled fan, coolant level is normal, no obvious leaks, ~30K miles.

[ November 27, 2005, 07:52 PM: Message edited by: dwheeler ]
 

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Daily Driver since 2/03
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995 Posts
Discussion Starter #3
Still running cold. Can I get a sanity check on this idea: If the normal cooling passage is blocked somehow, then the water pump would force the thermostat open with the pressure.
 

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FFCobra Craftsman
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22,700 Posts
Also a stock efi 302 w/ donor gauges.Noticed this weekend (45 degrees) it was running half way between middle line and the one below it.Maybe a little closer to the lower one.Usually thru summer it was a needle width below the middle mark while moving.I'm not concerned at all.If it continues as it gets colder I'll lay a piece of cardboard to cover 1/3 the radiator.
 

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Daily Driver since 2/03
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995 Posts
Discussion Starter #6
I tried the cardboard covering 1/2 of the radiator last night. It didn't change much except that for about 2 minutes out of 1 hour it stayed on the normal temp spot.
The uncovered part of the raditor was cold to the touch and the covered part was only lukewarm.
I don't know for sure if the fan was on while driving but it was not on when I pulled into the garage. I let it idle a bit and turned it off and the fan kicked on. Idling it seems to heat it up fine. I think idle would also have less pressure from the water pump to force the thermostat open.
 

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Junior Charter Member
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270 Posts
Correct me if I'm wrong but if your stat is installed correctly, the pressure from the pump acts against the stat. In other words, the stat opens toward the pump or against the flow of the pump. Your spring should be facing the engine so the pressure from the pump can't open the stat. I'm interested in seeing how this plays out as I believe mine runs too cold also.
 

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Senior Charter Member
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3,025 Posts
Is this a standard cooling set-up (T-filler, no degas tank)? Does the heater have a control valve and if you leave it closed (heat off) are the results any different?

The water pump shouldn't push open the thermostat and there shouldn't be any additional by-pass. Ford had flow restrictors in the heater lines on the Police version, but this was for blowing off the lines at high speed. I have a stock EFI with Vintage Air and the heater is enough to keep the temp gauge under 180 (T-stat temp), but it still blows hot.
 

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Daily Driver since 2/03
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995 Posts
Discussion Starter #11
I have the T-filler and have capped the raditor with a non-vented cap and plugged the overflow tube on the radiator. The heater has a valve and the car runs the same with it on or off. I use my heater a lot and it's never had a noticable influence on the water temp. Even if the valve is stuck open, it shouldn't cause the running cold thing.

You're right that the normal flow should be out of the engine, past the thermostat, and into the top of the radiator. The spring action of the thermostat is towards the thermal plug which is in the engine side. So normal water flow should not open it. But it's not running normal.

Maybe I'll run it with the cap off the T-filler and see which direction the water is flowing if at all.

The unit I just put in had the Prestone logo on it and seemed to match what I had before. I did buy it from Kragen since the Napa version did not have the bleed hole.
 

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I'd look at the sending unit for the gauge. As the engine warms up the ohms resistance will change. If it doesn't then the sending unit is bad. Another trick is to use a thermometer in the fill neck to see just how warm the coolant is. Regular cooking thermometer works fine. If these check out then the gauge is bad. Somtimes when putting in the new thermo it can slip down a little bit in the opening allowing coolant to flow thru the gap. Use a nonhardening sealant to hold the thermo in place when installing the the thermo housing.
 

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Mine runs around 165 when thoroughly warmed up with 195 thermostat. I have changed out two thermostats, checked them all in boiling pot of water, etc. and also used a laser temp gun to check against the gauge. Also, I have a manual fan so I know thats not on. Only time it has come close to boiling over was idling too much without any fan running. Oil only gets to 140 normally. Do they make higher thermostats?
 

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FFCobra Craftsman
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732 Posts
Put thermostat in a pot on your stove, heat it up, monitor temp with cooking thermometer, and watch it open. It should be close, but probably not exactly the temp that is on the label. Sounds like the thermostat is not working in your case. Stuck open or some kind of leak around it.
 

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"Mine runs around 165 when thoroughly warmed up with 195 thermostat. I have changed out two thermostats, checked them all in boiling pot of water, etc. and also used a laser temp gun to check against the gauge. Also, I have a manual fan so I know thats not on. Only time it has come close to boiling over was idling too much without any fan running. Oil only gets to 140 normally. Do they make higher thermostats?"

Something is seriously wrong. Where is your temp sender mounted, engine or rad side of the system. With a 195 t stat no coolant should flow untill that temp and it should fluctuate around 200-205 ish.
 

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I've got a question for you running cold guys, Where is your temp sensor/sending unit? The best location is in the intake manifold at the rear most location. You want the sender/sensor in the hottest spot. If you gauge is electrical check the sensor and the wiring. A high resistant condition will make the gauge read incorrectly. If you have a mechanical gauge the only location maybe closer to the front of the intake manifold. I've seen people with sender location in the radiator and that causes crazy readings when the outside temp drops.
 

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Daily Driver since 2/03
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995 Posts
Discussion Starter #17
My sensor is in the metal tubing that runs down the passenger side of the intake manifold to the heater. It's about 3 or 4 inches from the thermostat housing.
I was trying the boiling water test last night around 11pm. The gauge did not register anything at all with the key on an the unit in the water. The odd part is that the needle did creep up a bit when the key was off. I didn't think the unit needed a ground since it had 2 wires going into it. I'll try again with a ground wire...
I'd love it to be a bad sensor and it was just a lot colder than 50. I don't want to pull the water pump and try to pressure clean the water passages.
 

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Daily Driver since 2/03
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995 Posts
Discussion Starter #18
The guage is still dead. The temp sender is 45 ohms cold and 1 ohm in boiling water. This is close to what the book said about 73 ohms and 10 ohms.
Now I'm thinking it's a ground problem with the guage. But it stills nags me that the heater goes lukewarm when the guage does... Help! Make it go away!
 

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Senior Member
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Sounds like you have air trapped in your heating system. If ther air bubble is in the steel heating lines the gauge will read colder than it is. Try jacking the car up from the front as high as you can get it to remove all the air from the heater.
 

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Originally posted by dwheeler:
My sensor is in the metal tubing that runs down the passenger side of the intake manifold to the heater. It's about 3 or 4 inches from the thermostat housing....
DW, unless you wired your car considerably different from stock, that's the sensor for the computer.

The Temp "Sender," that sends its signal to the gauge, is on the forward LH side of the intake manifold (on a stock engine) just below and aft of the distributor.

Maybe that's why the gauge never moved. Your computer was probably saying WTF? tho!

btw, if you actually have your gauge hooked to the computer's sensor, well, I'm not sure the resistance and rate of change is the same as the sendor.

d

[ November 24, 2005, 08:26 PM: Message edited by: NAGA ]



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