78 J10 Running Cold after repairs

[Jklewer]

Strange things are happening... I'm in socal, it's currently 70 and sunny (sorry to some of you). Yesterday I pulled into my driveway after driving all day and my upper radiator hose sprang a leak for whatever reason.

Prior to today, operating temp has always been just a needle width or so into the green section on the temp gauge (no numbers).

Installed a new upper hose, therm (180 fail safe, same as what I removed), gasket, and rad cap. Didn't do much to bleed the system, just ran it until the tstat opened and topped it off at the rad cap. Been driving all day today (cleaning pools) and the temp is hovering mid way in the cold section of the gauge and I can verify this by the fact that my oil pressure is way higher than it normally is at all instances and because my hood is cold to the touch each time I stop at a customers house. Typical driving distance is 2-3 miles between houses.

This all might be ok besides the fact that my choke isn't resetting with the cool engine and the thing is running like crap from idle until 2000rpm or so. Whereas I just tuned it and it was running like a champ yesterday.

Any thoughts? Is 180 too low for right now (I'm currently sweating)?

Thanks, John

[tgreese]

Is a 180F what's called for by the factory?

OE temperature should be 195F from the factory. The engine will run better at the higher temperature, and you get no greater cooling capacity with a colder thermostat.

If you have a thermometer, put the thermostat in a pan of water on the stove and see when it opens. COuld be that the new stat is not closing completely.

But I would run a 195F.

[Jklewer]

That makes sense but shouldn't a new stat in 70 degree sunny weather climbing hills and driving normally stop and go be sort of irrelevant because the car would be at normal operating temp under the conditions? I guess I'm having a hard time believing my trucks cooling system is THAT good to keep the truck at 180 in today's conditions :/

[REDONE]

After carefully reading and rereading your original post, I can say forget about the thermostat. Yeah, AMC gen III V-8s where designed around 200*F and that's a fact, but it's also a fact that Idaho touches Nevada and neither fact has bearing on your problem.

I'm going to make an assumption and I hope you don't take offense. I'm guessing you don't have a tach and your estimating your rpms by ear. If that's the case, then I'm guessing that your truck runs crappy up to about 1200 rpm and then "catches" and runs normal. If that is also the case, then your timing is off. It could be because your dizzy gears are self destructing, your vacuum advance is malfunctioning or your dizzy just slipped a little out of time.

One quick question for you though, if you take the dizzy cap off, about how many degrees (or clock time) can you turn the rotor by hand, and roughly how much up and down play is in the dizzy shaft?

[Jklewer]

Redone, no offense taken. In my book, you take offense to those who have certifiably no reason to be telling you something. And you sir, do not fall into that category.

I'll check the shimmy tomorrow, I know my ford cap adapter has more room to move than I'm comfortable with, so that's a thought. There's still the fact that it's taking A LOT to get the thing up to operating temp compared to one day before (driving conditions are identical), based on oil pressures alone, not to mention the temp gauge which may have a bubble near it or something.

Today I charges down the freeway for 10 miles and the truck was almost to the temp where it operated all day yesterday. Just a thought.

[tgreese]

Redone, no offense taken. In my book, you take offense to those who have certifiably no reason to be telling you something. And you sir, do not fall into that category.

I'll check the shimmy tomorrow, I know my ford cap adapter has more room to move than I'm comfortable with, so that's a thought. There's still the fact that it's taking A LOT to get the thing up to operating temp compared to one day before (driving conditions are identical), based on oil pressures alone, not to mention the temp gauge which may have a bubble near it or something.

Today I charges down the freeway for 10 miles and the truck was almost to the temp where it operated all day yesterday. Just a thought.

Well, RedOne (ReDone?) has some interesting reasoning, but IMO you need to look at the obvious sources for the change in behavior. There is a principle called Occam's Razor, which in modern times is usually described as - when you have two competing theories about a single result, the simpler one is most often right.

IMO you went wrong when your hose sprang a leak and you did more than is needed to fix the problem. Now you want to compare the old behavior to the new behavior. Your problem now is that you introduced enough changes that you made my theory the simplest one, not RedOne's. He cpould be right, but then you have to assume that his timing change is coincidental with the hose leak, which requires an unlikely double-failure scenario.

My approach would be to rule out that the parts you chaged caused the different behavior. I would test both thermostats in a pan of hot water, and put the old thermostat and old radiator cap back. If your truck was not overheating, you did not need to change those extra parts.

And I would also run a 195F thermostat, not a 180F. But put the parts back first. And go easy on the sealant. And make sure that the 'stat is seated properly in the recess in the manifold.

[tgreese]

Also, I think you do not appreciate how the thermostat works.

A thermostat has a setpoint, given as its "temperature." Ideally this is the temperature that the thermostat is fully open. The thermostat is a negative feedback system - it has a gain, which is how much the thermostat opens in response to a change in temperature. Infinite gain would mean that the thermostat slams fully open when the coolant temperature reaches the set point. Then the stat would slam closed as the temp drops - this is not stable, and clearly not the desired performance. However, unless the stat has infinite gain, it will only approach the set point, not hold exactly at that point.

So the stat opens bit by bit until it's fully open. The faster it opens, the more gain, and the closer it will hold to the set point. The lower the gain, the larger the neighborhood around the set point, but the more stable its opening is.

Now, when you drive around, the thermostat should always open enough to keep you in that neighborhood of the set point. This should not be a lot of movement of your gauge, but it may be noticeable depending on the weather.

So if the stat does not hold the temp in the vicinity of the set point, the feedback system is not working.

[Jklewer]

Well here's the recently installed stat.

Thus, as you said, go easy on the sealer so you don't partially clog the bypass eh?

[REDONE]

This all might be ok besides the fact that my choke isn't resetting with the cool engine and the thing is running like crap from idle until 2000rpm or so. Whereas I just tuned it and it was running like a champ yesterday.

Any thoughts? Is 180 too low for right now (I'm currently sweating)?

Thanks, John

Your choke is reset by an electrically heated coil more than coolant or engine temp. Its the red wire with black tracer that also connects to the duraspark box. Even then your choke is thermal, unless it's getting cold (40* or so) your choke isn't doing much anyways. Running like crap off idle up to a sudden "VROOM" point, be it 1200 or 2000 is a timing issue, specifically the advance curve. Since my understanding of all things mechanical is so severely lacking (I dropped out after the second grade to be a nuclear propulsion engineer, one of the few fields that requires no formal education what-so-ever) I'll stick to what I know, pictures, block letters and bright colors.



Hundreds if not thousands of us are running 180* thermostats with no problems. Hundreds if not thousands of us have run with NO thermostat at one time or another without the problems you've described. The usual problem is overheating, often attributed to "too much flow" keeping the coolant from being in contact with the cooling surface of the radiator long enough to shed heat. I'm not convinced but I've never had that problem. Your one key problem "Runs like crap up to XXXXrpm" is textbook timing advance failure.

The simple test I proposed serves a lot of purposes. First, it rules out failed dizzy gears which is surpisingly common. More importantly it would bring anything obvious to light. If the dizzy is full of bright green slime, you'd see it. If the vac advance hose wasn't on the nipple, you'd see it, if the rotor was "crunchy" or "sticky", you'd feel it. It costs no money, takes no tools and can be done in less than a minute. If you came back and said "It barely moves up and down at all and I have about 1:20hrs clock time rotating the rotor by hand" I could say to check the vac advance hose back to the CTO and if it looks fine, you can check the CTO by plugging it and hooking the dizzy up to straight manifold vacuum.

I don't like seeing folks, especially new members go on wild goose chases, spending man hours and parts money not solving their problems. I like finding the problem and then spending the money, so I'm sorry it took so long to reply. It was a busy and emotional weekend due to real life stuff. Any pre-edit questions regarding my screen name could be answered here, but it's an old thread so I'm sorry most the pics are dead:
http://www.ifsja.org/forums/vb/showthread.php?t=134287
Last, I often say "Computers were supposed to make our lives easier, but really all they do is help us be stupid faster!". Life is too short to hold grudges and anyone who calls themselves an FSJer is a good enough friend to have a beer with. And if you don't drink, well, you're still welcome around my fire to watch me drink one.

[tgreese]

Re the choke thermostat, I don;t know what the relative contribution of engine heat (hot air from the choke stove) and electrical heat are to its opening, but IME you need both for the choke to fully open. Having fooled around some with trying to make junkyard parts from various Ford carburetors work as an electric choke, I suspect that the exhaust gas heating plays a significant contribution. I would suggest that the coolant temperature isn't affecting the fast idle very much. Some of these carbs have a bracket that holds the heater hose next to the choke thermostat, but if it's there, that would be lesser contribution to the choke opening.

I'm all for cheap and simple tests - pull the distributor cap and move the rotor around.

Checking the vacuum hoses is another good idea.

I hope I did not come off as highfalutin - just trying to help. The comments were offered sincerely - I think you have to look at what you changed first before you look for new problems.

[Jklewer]

REDONE, good post. The dizzy has about 3/16" up and down play. I marked the cap adapter at the two outer limits of the rotational play and there's a solid 5/8" between the two. Just FYI, the dizzy is new (reman) but of course I didn't touch the cam gear at that time.

Thanks again for your help. John

[Jklewer]

tgreese, no worries. I put the old 180 back in with a new gasket and no rtv, operating temp is back to where it was so were good there. The choke on this is auto though, not electric fwiw.

Also, I'm not offended in the slightest (by either if you guys), but am grateful for the help so I'm not floundering out here in california with an imminent smog check appt. Thanks guys. John

[REDONE]

The dizzy has about 3/16" up and down play.

Uh-oh. 3/16" is a bit much. When you turn the rotor by hand counter-clockwise, after you max out the spring tension of the mechanical advance, can you feel it turn a little more as the dizzy gear pushes the rotor out a little bit?

As much as it sucks, in my experience the A1Cardone dizzys come with soft gears that chew up fast and the spacers between the gear and the housing distort and open up clearance. If you don't mind resetting your timing, in your shoes I'd pull the dizzy to check the gear and spacers.

What carb are you running?

[Jklewer]

Turning ccw from rest, it "clicks" just a bit further before resisting. I don't mind pulling it but will likely wait since it's running quite well now that the operating temp is back up.

The carb is a 2150 (I believe) with no carb solenoid and the choke has a flat black "knob" without any plugs or anything protruding from it.

[tgreese]

tgreese, no worries. I put the old 180 back in with a new gasket and no rtv, operating temp is back to where it was so were good there. The choke on this is auto though, not electric fwiw.

Also, I'm not offended in the slightest (by either if you guys), but am grateful for the help so I'm not floundering out here in california with an imminent smog check appt. Thanks guys. John

Most of these automatic chokes are thermoelectric, having both a hot air connection and a wire to the choke cover. Your choke should still have a tube into the manifold for hot air heated by the exhaust crossover. Worth taking a close look at.

Glad you are making progress.