New Heat issues

[Anonymous]

Greetings,
I was having some almost-overheating problems after a top end rebuild that seems to have been a bad tstat. Now that it seems to run at a more normal, (but not as cool as it did previously), I have a new issue that I need help with:

When the temp starts to climb near the 3/4 mark, the Tstat obviously opens & the temp starts to go back down. That is good. But when I stop & turn the car off & leave it off for a few minutes, the gauge goes all the way HOT when I start it back up. Yes, it does drop again after it runs for 1 or 2 minutes, but that's 1 or 2 minutes where it IS HOT. What's up with that? Is the engine really that hot ? Is this something to worry about ?

What is the acceptable temperature range that these engines can safely run at? I will buy a real temp gauge tonight & install it. Any suggestions as to where to draw the reading from? Can it use the sensor in the head for an accurate reading?
Thanks,

David K
1963 Comet Convertible
Seattle

 

[MustangSix]

The the temp gauge will lag behind the thermostat anyway, but the temp will fluctuate like that as it heats up.

The condition you're experiencing is called "heat soak". When you shut the engine down, all that residual heat is transfered to the coolant and to the other cooler parts of the engine. The temps could easily go over 200 degrees and on some late model cars, more than 240.

This can have a couple of effects. First, it makes your carb more prone to vapor lock as the fule boils away. Second, it can affect anything that is sensitive to heat. like rubber, oil, etc.

One good strategy to avoid this is to allow the radiator fan to run for a few minutes after shutdown. I do this on my engine. I have a time delay relay that allows the fan to start and run for up to 8 minutes after the engine is shut off. I used a Nissan 280zx seat heater relay to do that. You could als just wire a fan to run anytime a preset temperature is reached, but that might allow the fan to run on for quite some time and kill the battery.

Hood vents, louvers.....anything to relieve the heat.

 

[66200i6]

The combination I like is the adjustable t-stat that reads the radiator temp. The power to the fan control is always on. With this setup, it doesn’t matter if you’re running or after you shutdown, the fan will run when it is needed. After shutdown the coolant system looses it ability to remove the heat efficiently because the fan and the water pump has been disabled. Fortunately we still have this thing called convection working for us. If the fan is wired as above, the t-stat will call for cooling to a point where the heat has been removed from the rad. However the coolant will continue to move from the block to the rad. through convection. After the rad. has absorbed the heat from the coolant again, it will turn back on. The fan doesn’t run more than a few seconds each time and it is surprising how quickly the block will cool. I’ve seen the time it takes to cool down after a quarter mile run, drop from just over an hour to just under 15 min.

If you want to save the cost of a $40 - $60 controller you can use the GM type temp sending unit mounted in the block instead. The sending units are set to open at a know temp so the fan will work the same, but you will have to find the right sending unit that will make your system work.

Good luck, Ric.

 

[CobraSix]

jack,

Just out of curiosity, how does having a fan run after shut down really help? It will cool the water in the radiator, but what he is experiencing is the coolant in the block heating up since there is no longer any flow to the radiator. As soon as the car is restarted, the flow is re-established and eventually the temperature gauge goes down. I just don't understand how a fan blowing after the engine shuts down does anything except cool the coolant in the radiator, unless you are counting on the fan moving the hot air in the engine compartment around.

Slade

 

[MustangSix]

Even when the pump isn't running, there is water flowing thru the system due to the thermal siphon effect. The cooler water in the radiator sinks, flows to the engine, and displaces hat water in the engine. Many early prewar engines relied on this action alone without a water pump; my MG J2 was one of them.

It makes a big difference in engine and underhood temps. For example, V12 XJS Jags are notorious for dying young. That problem is mostly due to the heat build up in the tight engine compartment. Hoses get hard, gaskets fail, electronics die, a whole raft of problems arise. Simply running thr fan for several minutes after shutdown extends the life of all these components by a quantum leap.

 

[Anonymous]

Well thanks, I appreciate your input, but here's 3 problems with those suggestions:

1- I don't have an electric fan. Yes, I can add one, but that won't look very stock & may add new problems. (yes, I'm trying to keep it stock, visually).

2- I want to fix the root problem, not attack a symptom by adding more variables. Why would rebuilding a head & re-ringing pistons cause new temp readings? Nothing is really different in there. I liked it better before I rebuilt it because it ran cooler & didn't do strange things.

3- What is the target temp range for the 170 & what is the hottest it can safely hit? Any ideas here would be helpful since I will be adding a gauge with actual numbers on it tonight.


Also,
What is an adjustable tstat & wouldn't it be better to connect it to the sensor at the back of the block where it's hot instead of the radiator, where it's less hot?

Should I try water wetter or a 165* Tstat? My old head worked great with the 192* & I currently have a 180*.

Thanks. No really. Thanks,
David K
63 Comet

 

[MustangSix]

1. Hmmm, For some reason I was thinking you had an electric fan. Please refer to the ADDHD thread!

2. Water Wetter is also a crutch. One thing I always recommend is to use a really good thermostat. Stewart or Robertshaw are the best. The cheap ones do not open consistently and sometimes stick. If you haven't tried that, give that a shot. Re ringing can cause a rise in temps because you'll have just a bit more friction until the engine breaks in again.

3. 180 is about the right temp for most conditions. You have to allow the engine to get warm enough to evaporate the condensation and get the oil at the right viscosity.

 

[CobraSix]

My car does that all the time. I don't worry about it, it's part of the older cars. I've never had a problem with it. I think it's merely caused by the flow of coolant stopping and the engine is still warm but there is no cooling water circulating. It caused the temps to raise. We used to use it as a trick to get the engine temps of marine diesels up quicker so that wouldn't blow as much smoke.

Slade

 

[Anonymous]

Hi, DkComet;
The heat soak phenomenon is very common with cast iron Ford engines. It causes no problems, so long as everything else is set up properly. In fact, it cures the rings and cylinder bores for longer life by de-stressing them with long, gradual temperature treks. Ford has much published literature about this effect. The unexpected feature of this temperature travel is this in particular: all else being equal, the cylinders will last 50% longer at 195 degrees t'stats!

If your engine is running a 180 t'stat, it will climb to about 220 when you shut it off. If this bothers you, try removing the gasket across the rear edge of the hood to let some of the heat out - or install louvers or scoops in the hood (this was popular in the '60s).

DO NOT run less than a 180 t'stat on a cast iron engine or you will experience very accelerated wear, especially in cylinder #1 where the water pump feeds the block.

Two more things: in a new engine, this effect will be more pronounced until the engine breaks in a while, about 10,000 miles or so. Ford recommends this on new engines from their factory: set the idle at 25-50 RPM LESS than 'normal' idle. For instance, the 200 idle is supposed to be 650 RPM, but the Ford manual says to set it at 600 when new, as the idle will increase to 650 when the engine breaks in. This lowered idle speed helps lower the 'heat soak' amount, too. Also, try opening the idle jet screw an extra 1/4 turn. This will slightly lean out the idle mixture, which will reduce the afterburn in the exhaust manifold - this will lower the underhood heat buildup.

Hope these tips help!

 

[Anonymous]

Thanks Mark!!!
Great info. I need to figure some stuff out with the carb to get it adjusted right. I still can't get a smooth idle & have bumped the timing up & the idle too. The book says something like 550 rpm on the automatic when in gear at a stop. Mine is more like 650 now or else it's really bumpy. I'll work on that. I may need a new carb.

I can't figure out what else is causing rough idle. I have new plugs, points, cap, rotor, etc. I may need to look into the ignition stuff. It's not original, but it's not new either. No idea what it is. I works so I haven't messed with it.

I went back to a 195* Tstat because the engine used to run cooler when I had one of those, but thought the one I had may have been bad & I really thought that a lower temp Tstat made your engine run cooler. I understand now that it's the opposite of what it seems like it should be.
Keep your fingers crossed.
Thanks for the help!

David K
63 Comet

 

[weeds]

I have had this 'problem' for several years, and it always turns out to be low water. When the pump turns off, the water drains out of the head, leaving no coolant there. If the system is properly 'burped', then my problem goes away. You said it is stock appearance, so I assume that there is not an overflow catch can? The red-neck solution is to drill a 1/4" hole in the t'stat.

 

[Anonymous]

I did make an over flow bottle because my radiator used to burp after a long drive & spew coolant all over my horn/frame area & it would rust it all up. Problem solved. I need to find a period vintage bottle of some sort to look more original.

Would the drilling a hole in the Tstat cause problems down the road? I thought about a smaller hole, but decided to keep trying without cheating. I was also wondering about the air pocket issue. Haven't noticed it as a problem on the past. Any advice on how to make sure all the air is out of the system (burping)?

Thanks,
David K
63 Comet

 

[addo]

An experienced engine builder once opined to me that a principal part of the rings' function was to transfer heat to the cylinder walls. Viz; you have gained some efficiency in combustion sealing.

Similarly, if the head has been hot tanked, the insulating layer of scale is gone. You are now getting more of the "truth". A question: Did you allow the radiator to fully dry out while the head was off?

Adam.

 

[Anonymous]

Adam,
I suppose the radiator did dry out while the head was off. It's a newer radiator & there appears to be no rust inside though. Could drying it out cause a problem? What's the angle here?
David

 

[addo]

Well, I was just getting at that tendancy of older radiators to flake internally when dry. A cooling system flush is helpful, but not a major salve. Timing issues are major contributors to hot running, as are exhaust restrictions (poor valve lift, blocked exhaust). The original style radiators were pretty borderline. A three core downflow with 14 fins instead of 12 per inch is a good start and looks stock. A slighly larger fan (if it will fit) may be another option.

Possible, but unlikely, are clearancing issues with the valves/guides after the head work.

Let us know what the numerical gauge reads.

Adam.

 

[Anonymous]

Hi, DK;

I notice you said you bumped the timing up a little. When I do this to my 200, it always increases the underhood heat and heat soak. I like it in the winter: it keeps the engine (and heater) warm longer when I'm 'store jumping' on the sub-zero weekends. But, in the summer I run it at 6-8 degrees advance to reduce that heating effect. I get better gas mileage with less static advance, too, and no vapor lock. At 12 degrees BTDC it's a vapor-lockin' son-of-a-gun in warm/hot weather, but at 8 degrees it never happens. And here in Colorado, summer is a 100-degree affair.

Just as an experiment, set the timing back to 6 degrees. You'll have to readjust the carb for an idle. See if it cools off some.

Also, try tightening up the screws that hold the top plate of the carb onto the carb's body. I'd bet my long screwdriver that you'll find loose or stripped screws in that collection. If loose and they tighten, it should work better, but may not fix the whole problem. If the carb is over 40,000 miles old, consider a rebuild. The traits you are describing mimic the scenario where the power valve is dropping open at lower engine speeds, causing a rich mix. One test for this: when the engine is cold, try turning the carb's air screw all the way in at idle. If the engine does not die, the power valve is leaking gas into the venturi and needs replacement.

 

[Anonymous]

Now I'm really confused...I too have temperature issues, but I am now reading seemingly conflicting advice on Timing adjustment and engine temp. I have seen advice in both directions...advance the timing to 10-14 degrees for cooler operation, now I see drop the timing to 6 degrees for cooler temps...Asuming that we all have our idles and mixtures set at reasonable rates, WHICH IS IT?
Very confused...Bob

 

[MustangSix]

Normally, retarding the spark can increase heat in the engine. Stuck advance mechanisms which prevent the advance from working are known killers of Jag V12's, for example. On our inline engines, excess heat at high rpm can sometimes be traced to a bad vacuum advance mechanism on the load-o-matic distributor.

However, in some extreme cases where detonation is a problem, taking some advance out may reduce engine temps.