Cooling mystery...

[JeepSnake]

OK gang, I have a mystery on my hands. I rooted around many an engine compartment at Homecoming, talked to several people, and still have no answer.

The coolant temperature in our FIA car will not stabilize. It doesn’t overheat; it just doesn’t come to a stable temperature. The car heats up to 180 degrees, thermostat opens, temp falls to 160 degrees, slowly rises to 180 again, t-stat opens, temp falls to 160 degrees, and so on. It just will not steady out around 180 degrees like it should.

The cooling system is identical to Dad’s 427 car: nothing but radiator, water pump, 180 degree stat, inline Moroso filler, 16 pound Stant cap, and a Canton coolant recovery tank over on the passenger footbox. With both the original 302 and now the 383W stroker, Dad’s car runs a rock-steady 180 degrees. With our 351W, we get the ~20 degree fluctuation.

Now, here’s where things get stranger. This exact same 20 degree fluctuation was happening when we bought the car. Only then, it had a 160 degree stat, and the variance was between 140 degrees and 160 degrees. I changed the stat, thinking I’d warm the engine up as well as fix the problem, but the fluctuation remained, just shifting upwards. I’ve also changed the temp gauge and sending unit – identical readings, so I’m not dealing with a gauge ghost. I’ve filled, bled, and otherwise made sure that the air is out of the cooling system. I’ve even moved the temp sensor from one coolant port to another in the intake just to see what happened, but no change!

Thermodynamically speaking, the only real differences between the two cars is that our FIA car has an oil cooler and iron heads, whereas Dad’s car has no cooler and aluminum heads. Still, it looks like the thermostat would even out the temperature right around 180 or 185 degrees.

So, anyone have any ideas? I’m convinced that I'm "too close to the issue" and there’s something minor that I’m overlooking. (I suppose the only thing I haven’t been into is the water pump; but what could be the problem there???)

[TurnpikeBoy]

Do you have a heater? If not, is the hose between the T-stat housing and the water pump hooked to the UPPER pump spigot (and the lower port blocked off)? Not that it's easy to do otherwise, but the upper is the -out port, and the lower the -in port. If you're hooked to the lower, it will pull water thru the engine regardless of whether or not the T-stat is open, keeping the engine generally cooler (since it's only a small hose, it won't pull lots).

It's a thought.

[brfutbrian]

zach, youre worrying too much and overthinking. youre fine, just enjoy. later, brian

[JeepSnake]

Turnpike - no heater on the car. Bypass hose from t-stat housing does connect to upper pump connection, lower pump connection is capped. I am in the process of installing a Harrison expansion tank right now which will be connected to the lower port.

Brian - oh, I'm not worried about it. The car runs great and I sure don't hesitate to drive it. Just in the process of installing the expansion tank, and I got to trying to figure out what's going on since the other identical system runs at a steady temp.

BTW, anybody know what pressure radiator cap I need to run with the Harrison tank when I finish installation? I've got a 16 psi now, but think I remember seeing that 13 psi was correct for the Corvette expansion tank to keep it from swelling.

[Aggressor]

Zach - Of the three cars that I've built two were small blocks. I have never experienced a small block running as cool as you are reporting. This does'nt explain your temperature fluctuation but if you have used teflon pipe tape when installing your sender unit it could read 20-25 degrees cooler. The tape provides a poor gound to the intake yielding incorrect readings. I now use a teflon pipe sealant paste.

My first car about made me crazy with this problem. Some of my radiator hose connections would blow apart from time to time, at the most inconvienient moments. Clouds of steam and antifreeze everywhere. I had set the fan thermostatic switch to come on at about 195 degrees and to quit at 180. In reallity the fan's upper limit was 220 degrees with cut-out at 205 due to poor grounding of the dash gauge used to set the limits.

Your 20 degree swing does'nt sound bad but a 160-180 range seems too cool for the engine running temp.

-Geary

[ralphscott]

Zach I am running a 13 lb cap. I'm sure you also bled the top of the intake to get any air out of the system.

Ralph

[Brent]

Up the compression to 12-1
put a larger cam with a lot of duration in

It will stay on the thermostadt all the time

[brfutbrian]

geary, never thought about teflon tape making a bad ground, but it sure could.

brent, i know what you mean. you gonna make it to gadsden next year ???

zach, with the temps youve got go with the lowest pressure cap you can find. the only thing 16 lbs of pressure does is raise the boiling point a few degrees and put that much more pressure on your cooling components. later brian

[JeepSnake]

OK, I picked up the correct 13 psi cap at lunch. I should have about all the parts accumulated now to install the tank.

Ralph, I actually installed a radiator petcock in the intake coolant tap right behind the t-stat (the one that would normally be used for a heater hose). When filling the system, I just open it up to let the air escape. You'd be amazed at how many people ask me, "Hey, isn't that a radiator drain behind your distributor? What's it for?"

Geary, I'm going to recheck the electrical continuity with a meter. I typically use Permatex #2 on ground-type sensors just for the reason you describe.

[wlewis]

Zach,
My 351W temp fluctuates similarly to yours. Seems mine goes up to about 190 and then backs down to about 170 or so. I believe my thermostat is 180, but can't remember exactly. I do have a 13psi cap. I like your petcock on the manifold idea.
Walter

[twanita]

the guy at alumarad.com is kind of a "water temp jedi" and very helpful. talks about your fan fighting against the mechanical thermostat. i added one of his 180 deg in-hose elec stats for my puller fan and it stabilizes well with a 180 deg mechanical thermostat. it kicks fan in when water temp going into the engine reaches 180 deg.
see photos of the setup on the attached thread.

http://www.uniquecobra.com/forums/showthread.php?t=7298&page=2

[nolastyankee]

Zach,
Our 351W and my 289 Mustang both fluctuated up and down with the thermostat opening and closing. With our car I have noticed just how efficienc the aluminum radiators are and it is more apparent than on our Mustang.

[bittentoo]

Zack,

Did you drill any holes in the t-stat? If so then it/they are to large and the t-stat is opening and shutting right off of the seat.

Does your fans kick on automatically, if so then the temp setting is too low.

[ralphscott]

Sounds good Zach hopefiully the 13 will help. Mine runs steady no significant fluctuatuon when I have the fan on. Fan off at idle it keeps on a climbing...

Ralph

[Naumoff]

Put a piece of card board in front of the radiator and cut a 16" hole in the middle of it.
Trucker Style [thumb]











;)

[Ed]

Just a thought
All thermostats are not alike,,,,ae. Stant makes 2 diffrent models.. the better is designed to modulate water flow better.......my guess is that the water cools in the radiator when the thermostat is closed and when the cooler charge circulates upon the stat opening it regisrers and then causes the seat to close....the cure is to drill a hole in the stat to allow some circulation even when it is closed.
Just an idea
Ed

[JeepSnake]

Guys, here are some answers to your questions, as well as some photos of my Harrison expansion tank installation I completed today.

Kelly - one hole in the t-stat to bleed air. Only 1/8" diameter at 12 o'clock. Identical to every other vehicle I've got.

Ed - I suspect you are on the right track. My brother reminded me of a car we worked on that had a t-stat that didn't modulate; it was either full open or full closed, and it had a little lag in its response. I think the guy wound up using a Robertshaw t-stat to solve the problem. I'm going to look into a better one.

In the meantime, I went ahead with installing the Harrison tank. In the photos, you'll see that I went with a rather unorthodox location for Unique FIA cars. I did this for two reasons:

1) The way the oil temp sending unit is installed killed the vertical space available for mounting forward above the oil filter (the typical location); relocating the filter unit or temp sender wasn't something I wanted to do, as I like where they are. Plus, it seemed a little low for the 351. (I wanted the tank to be the highest point in the system.)

2) The earliest original cars mounted the Harrison tank off the driver's side head. The tank was turned 90 degrees from my install, though. I compromised there. To mount "as original" would have required a 1961 style Vette bracket, priced at $120. I think it would have interfered with the steering shaft setup on the Unique car as well. To mount like I did used a 1961 - 1972 style Vette bracket, priced at $10 (plus a piece of scrap aluminum).

So, that's why I wound up doing it the way I did. It worked a-okay on my test drive this afternoon, and I'm very pleased with how it turned out looks-wise!

Oh, and yes, I am going to take the Moroso inline filler out of the upper hose. Just another project for another day right now. I put my old 16 pound cap on it to seal it for now, while the functioning 13 pound cap is on the Harrison tank.

[RJacobsen]

looks good Zach, Where did you connect the larger lower hose from the Harrison tank?

[eliminator]

:BEER: , Looks good to me, good work.

[ralphscott]

Nice job Zach you made it look like the space was made for it!

Ralph

[Naumoff]

Looks Great [thumb]

[JeepSnake]

Thanks, y'all!

Rod, the lower/big hose on the tank is connected to the lower water pump hose nipple on the 351. This is the water pump connection that would normally have a heater hose routed to it.

[RJacobsen]

Thanks Zack, from what I have gathered from other photos that looks like the most common location. I'm considering connecting mine to the lower radiator hose, are there any problems anyone can think of with that location?

[Slither]

Did you ever sort out the temp fluctuation, Zach?