Overcooling?

[peeeot]

Ever since I put this rebuilt 200 in, the temperature gauge never goes any higher than the very bottom line of the "good" range. The old motor used to take the needle up into the lower third of the "good" range.

I put a thermometer into the radiator right after driving and the temp was around 170, and since the manual said it should be at least 180, I assumed the rebuilders had used a 160 degree thermostat. I tested a spare 180 degree unit (from the old engine) and it only opened about 3/16", so rather than reuse it I bought a new one. I immersed them both in water and let it warm up to boiling. The new one started opening at about 183 degrees, and was wide open, more than 1/4" around 210. The old one didn't start opening until about 187 and it opened more slowly and not as much (like before). So I installed the new one and didn't bother to test the old, knowing that the new one worked properly.

Lo and behold, the temp guage still doesn't cross into the "good" range, and the thermometer still gets 170 degrees in the radiator.

Is this a gauge problem or a sender problem or no problem at all?

I should add that this is an a/c car with the 6-blade fan.

 

[pedal2themetal45]

actually I don't see a prob.. was the stat you took out a 160 ? or a 180 ? ... if you have to have a 180* motor put in a 195* stat... I also would put in a mechanical gage to see what it really is..
tim

 

[ludwig]

I don't see a problem - period. The temp gauge is not a precision instrument. All the temps it shows are relative. You could get an aftermarket dial if you really want to know what really is happening.

If the engine gets hot enough to drive, you should not have a problem. Depending on where you live, it might be an advantage to not get real hot to start with so you'll have more margin when the weather gets really hot. I have a 160* gauge and it always sits on the low side except on 100+ days. Then it goes up to the 'normal' range, which probably says something about the weather in Southern California. [What's 'normal'?]

 

[66 Fastback]

I agree with Ludwig. Unless you see signs of condensation in the oil that would indicate that you are not getting hot enough to boil off the water vapor, I would not worry about it. If you replaced the temperature sending unit, your gauge will probably not read correctly. Most of the replacement sending units are calibrated differently or respond differently than the original unit. When I installed my engine I used a new sending unit and like you, the gauge did not read in the normal zone even though the coolant felt hot. I pulled an original sending unit off of another engine and the gauge read normally.
Doug

 

[wallaka]

The stock gauge just says, "Heat? Yeah, you got some." That's as precise as it gets. Get a real gauge, with numbers, if you want to know how hot it is.

 

[peeeot]

Maybe I have too much modern car theory in my head. Part of the reason I've wanted to nail this issue down is because I know how much difference proper warm-up makes in modern cars. Sure, they run hotter for emissions purposes, but the system still depends on a standard operating temperature and if it never warms up that far it is essentially out of its normal operating parameters. I was assuming that operating temperature is part of the equation in carburetor design/calibration as well, and that it was therefore still important that it got as warm is it ought to.

If it's supposed to run at 180, and it IS running at 180 but the gauge points to the bottom of the good range at 180, well, that's fine with me. The old motor must have just run hotter due to a thermostat that didn't open all the way.

I used either silicone or Formagasket #2 to seal the threads on both that and the oil pressure gauge; both of those should be fine right?

Sorry everyone, I can be kinda obsessive about little things like this sometimes

 

[350kmileford]

I agree with you , peeeot. I've come to believe that there is not only a maximum operating temp, but a minimum as well. A minimum temp usually means that all of the internals have expanded to their proper size and everything is flowing properly.

 

[CobraSix]

There is definitely a TOO COLD. I would also say there is too hot, the point where the coolant is boiling over the cap. While I firmly believe that the 200 should be running with a 195* Tstat as designed, I also think it's a good idea to adjust that to local conditions. From my experience, driving in everything from 10*F to 100*F with my mustang I've found that with a 195* T-stat and a properly operating cooling system, the mustang shouldn't overheat in most conditions. However, I wouldn't live in Pheonix and drive with a 195* Tstat...

But again, I couldn't get by with a 160* Tstat either. I have a 180* Tstat in right now, but that is borderline too cold for winter driving. If the temp is below 40* outside, the car barely warms up enough and with my current engine set up, it is very cold blooded and wants to be warmed up to run smoothly, much less to actually have heat running inside the car. I've just been too lazy to replace the Tstat back to 195*. I put it in the head when I was having some cooling system issues a while back, only to find out my radiator was junk. Next time I drain the system I'll put a 195* back in.

I do agree, pay no attention to the position of the Temp gauge. It's okay for relative gauging of temperature, but not accurate like modern gauges tend to be. If you know your car is running at 180* and the Gauge is pointing just at the normal line, then there is your baseline temp.

 

[rust collector]

Wouldn't the gasket goop act as insulation, and if the sensor has a "bad" ground, would it not read low? :

 

[66 Fastback]

You might try something different to seal the threads of the sending unit. I honestly can't remember if sealant will cause the sending unit to operate improperly. (I know I read it one time). But I would think that if it is poorly grounded it could affect the readings. (the NPT threads are a tapered interference fit so it should make contact, but maybe the sealant is increasing the resistance. Is there an electronics expert in the house?
Doug

 

[69.5Mav]

66 Fastback

Yes there is. If the case of the temp sender is isolated from gnd it won't work. You need a return path for the current to flow. The Temp. sender is a temperature variable resistor. As the temperature goes up the resistance goes down and the current in the circuit goes up causing the gauge (a current meter) to deflect more from its zero position, indicating a hotter temp.

peeeot

Did the Temp. sender get changed? They do not all of the same resistance characteristics. Look for a nice shinny new one. The senders also change as they age. Using a resistance meter with the gage unhooked you can measure the resistance of the sender at various temps and construct a chart of resistance vs. temp. You can use this to track the senders change over time if you like. So you can see that there can be several issues affecting how high your gauge goes.

1. Poor contacts in the system causing extra resistance
2. A new/different/drifting sender.
3. A gauge (40 years old?) that has changed
4. A cooling system that has changed/gotten better.

All these things can change the way your gauge reads

69.5mav

 

[Lazy JW]

You might try something different to seal the threads of the sending unit. I honestly can't remember if sealant will cause the sending unit to operate improperly. (I know I read it one time). But I would think that if it is poorly grounded it could affect the readings. (the NPT threads are a tapered interference fit so it should make contact, but maybe the sealant is increasing the resistance. Is there an electronics expert in the house?
Doug

Brass threads properly dimensioned really don't need a sealer at all due to the destructive interference fit. Some copper-type anti-seize won't insulate though and will seal just fine.

The stock gauges really are pretty feeble. The Instrument Voltage Regulator (IVR) that Ford uses has a bi-metallic strip that "pulses" the signal to the gauges. The IVR accomplishes this pulsing by heating up, breaking the circuit, then cooling back down to re-establish the circuit, on and on.... Well, guess what? This heating, cooling, heating, cooling cycle behaves differently depending on the AMBIENT temperature under the dash. Simply running the defroster warms it up under there enough to make a significant change in the gauges (temp, fuel, and oil pressure) on my 81 F-150.

I have verified the temperature on my engine with an infra-red thermometer, the fuel gauges are tolerably accurate now, and I have enough oil pressure that nothing knocks so I'm happy. But I had to adjust the IVR output to get the gauges to read up where they should be, they all read way low even with a new IVR.

I'm running a 205º stat in my 81 F-150. This pickup has the dinky stock radiator but it has done fine in temperatures ranging from -30º F to 102ºF.

I don't like cold running engines. They aren't as efficient.
Joe

 

[fordconvert]

I/O marine engines (at least in the 70's) ran in the 120's. They are always nasty and slimy inside due to not running hot enough to burn off moisture. I assume the new EFI stuff runs around 200 like modern cars. I would think 170 is fine. You can get one of those digital IR probes to get a good idea what actual temps are. I think I got mine for $40.

 

[rmoe88]

If your car is also taking longer than normal to reach a colder than normal temp, it could be that the Thermostat was installed incorrectly. I figured that one out by experience. What happen to me was the Tstat slipped out a little in the housing when i was bolting it on. It was just a sliver of a gap, but it was enough to over cool the engine. Hope this helps.

 

[woodbutcher]

OR,you can do what I did for a thermometer to check the coolant temps.I got a Pyrex(R)brand candy thermometer for $7.00 on sale and it works fine.And it is pretty darn accurate
Leo

 

[peeeot]

...I firmly believe that the 200 should be running with a 195* Tstat as designed...

This is the crucial information for me. I assumed all along that a 180 degree thermostat is what it was designed for. The manual lists specs for 2 thermostats, a "low temperature" one and a "high temperature" one; the low opens at 160 and is fully open at 180; the high opens at 190 and is fully open at 212. The one I installed is in between: opens right around 180, fully open around 200. I don't know why the manual isn't clearer about which to use, but if the motor is designed to run with a 195* Tstat (where did you get that information?) then that's what I want to have in it.

The gauge in my car has always been consistent and reliable. I know it's grounding, but I don't know if the resistance is too high, causing bad readings. Someone told me Teflon tape would work correctly; do you guys agree? Is there supposed to be a ground strap for the motor?

I'm using the same sending unit that I had in the old motor.

As I said before, the Tstat that was in the old motor didn't open nearly as far as the new one, nor as soon (even though it's stamped as being a 180* unit also). So I suspect the old motor ran hotter because of that, and the gauge indicated accordingly.

So are most people using a 195* Tstat then? Efficieny is my top priority though it clearly warms up enough to produce an average compression reading of 210psi as-is.

Oh, I also wanted to note that the heater doesn't feel as hot as I remember it being. I would think that in warmer weather, it would be oppressively hot. It isn't. This also makes me think it should be running warmer.

 

[woodbutcher]

The heater core could be partially plugged.Have it flushed,or flush it yourself.If that does`nt do it,replace it.
Leo

 

[Lazy JW]

....

So are most people using a 195* Tstat then? Efficieny is my top priority....

195º is the coolest I would even consider for best economy.

Teflon tape will work fine but I prefer the goopy stuff.

Definitely install a ground strap. There is no such thing as too much ground; it may well be adequately grounded elsewhere but I wouldn't count on it.
Make sure it is grounded to the frame AND the body.
Joe

 

[fordconvert]

Make sure it is grounded to the frame AND the body.
Joe

Frame? Thats a good one. Us Falcon/Mustang/Ranchero people dont need frames. You truck guys have have a sense of humor. Next thing you guys are going to say your 'frames' are made of something other than 14 gauge sheet metal and would hold the drivetrain together without the body?

 

[Lazy JW]

Make sure it is grounded to the frame AND the body.
Joe

Frame? Thats a good one. Us Falcon/Mustang/Ranchero people dont need frames. You truck guys have have a sense of humor. Next thing you guys are going to say your 'frames' are made of something other than 14 gauge sheet metal and would hold the drivetrain together without the body?

Sometimes I forget where I am
Reckon that is ONE advantage of a unibody; only one ground strap is needed.
Joe