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Discussion Starter · #1 ·
So I have an odd thing going on with my 72. (383 stroker 700R4) Every time I take the car out, the temperature initially climbs to 220 + for not even 30 seconds and then cools down over the next 5 minutes or so and then settles in around 185 / 195, it will then run around 190 forever or until I shut the car off and it cools completely. I have a Robert Shaw 180 degree thermostat (which I tested in a pot of hot water, it does open @ 180) , factory fan shroud, factory radiator, 7 blade clutch fan, Auto meter water temp gauge. I have burped the system with the funnel kit 2x and have an overflow tank, the car does dump some antifreeze in and out of the overflow tank every time I drive it.

Any idea why the thing spikes so high initially? Is this something I need to be concerned about ? I have researched this online a ton, but I just can't find anyone who is experiencing the same type of scenario. I'm new on Steves Nova ( been lurking for years ) so I think this may be where I can get some solid advice.

My one car buddy says to not worry about it, just not sure.

Thanks in advance - Jay.
 

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Also, where is your temp sending unit? Intake manifold or in the head? Just curious... Manifold would lead me to believe the thing needs better burping and the bypass hole in the thermostat @Mike Goble stated is key to removing all air and keeping a slight flow for removing all the remaining air over time. As @Shane65 mentioned, you need to rev the engine to flow the water to catch the air. Just idling it will not work. Clutch fan engaging properly? Have you watched/listened to it during the initial warm-up?
 

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66 Chevy II, 871 blown 355
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I have done allot of studies on cooling my 66 over the years as I have a 871 blown 355 in it and had always had issues controlling it.
I have a data logger in the car and made this test at one point to see what effect the bypass holes in the thermostat had on the cooling system. Here is a pic of the results I found. The top chart is a startup WITH the bypass holes in it and the bottom is WITHOUT.
You can see the difference in the temps from the Engine Manifold to the RadTop, which is the output from the engine atter the thermostat.
Without the bypass holes, the engine heats up until the thermostat opens, then the two temps will "Come together".
With the bypass holes the temps will climb together.
I like the bypass holes in place to avoid the thermal shock when the thermostat opens but I also find the engine has a hard time creating heat on cold days for the heater inside the car.
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I've always noticed on my cars that the temp overshoots 180 deg F and then comes back down after the t-stat opens. I'd call that normal and as long as you notice a downward temp trend after the t stat opens, your good. Brian, that is great info. Data is a good thing.
 

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Discussion Starter · #10 ·
Did you let the cooling system get to it's maximum temperature with the heater on full and the thermostat open? You also have to rev the engine to get the stubborn air out.

How to Burp Cooling System | Subaru WRX STI | - Bing video
So I followed the directions on the funnel kit, I couldn't remember exactly what the procedure was so I looked last night. The directions specifically say to run the engine at idle during the "burping" process. I revved it up a bit anyway but maybe I didn't get aggressive enough ? Thanks for the help.
 

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Discussion Starter · #11 ·
Also, where is your temp sending unit? Intake manifold or in the head? Just curious... Manifold would lead me to believe the thing needs better burping and the bypass hole in the thermostat @Mike Goble stated is key to removing all air and keeping a slight flow for removing all the remaining air over time. As @Shane65 mentioned, you need to rev the engine to flow the water to catch the air. Just idling it will not work. Clutch fan engaging properly? Have you watched/listened to it during the initial warm-up?
Thanks for the advice Ace, as you can probably see from my other responses, I likely didn't rev the engine enough to get all the trapped air out? My temp sending unit is in the cylinder head. The clutch fan will not spin more than half way around with the car off and engine cool.
 

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Discussion Starter · #12 ·
I have done allot of studies on cooling my 66 over the years as I have a 871 blown 355 in it and had always had issues controlling it.
I have a data logger in the car and made this test at one point to see what effect the bypass holes in the thermostat had on the cooling system. Here is a pic of the results I found. The top chart is a startup WITH the bypass holes in it and the bottom is WITHOUT.
You can see the difference in the temps from the Engine Manifold to the RadTop, which is the output from the engine atter the thermostat.
Without the bypass holes, the engine heats up until the thermostat opens, then the two temps will "Come together".
With the bypass holes the temps will climb together.
I like the bypass holes in place to avoid the thermal shock when the thermostat opens but I also find the engine has a hard time creating heat on cold days for the heater inside the car.
View attachment 440470
Wow, this is GREAT information, thank you so much for taking the time to post this. So in your opinion, do you favor the bypass holes ? Also should there be 1 hole or 2 ?
 

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Discussion Starter · #14 ·
Wow, thank you all SO much for taking the time to reply and try and help me ! The only regret I have at this point is not coming here for advice sooner, this is great. I wanted to add a few details that I forgot to mention yesterday that may mean something to you guys. When the car is doing it's crazy temperature dance I can lower the temp by 10 degrees easy by simply getting on it. You can watch the temp go down as you accelerate ? Also, I just noticed yesterday that the capillary tube from the gauge to the sending unit has at some point laid down on the header. It's impossible to see from above but I was poking around with my inspection mirror and noticed it last night. There is a definite flat spot on the bottom side that you can feel with your finger, the "coating" or "jacket" that covers the tube is melted clean away, the tube is not leaking and it is in no danger of touching anything hot now but I know it's not right. Could this be my "smoking gun" or just a coincidence? And lastly, when I tested my thermostat (Robert Shaw 180) in a pot of hot water, I noticed it started to slowly open @ 180 then maybe fully open at 190 ish ? Is this normal or should the thing "pop" open @ 180? Thanks SO much for all your help.
 

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Are you sure your clutch fan is working? You may also want to post a picture showing how you fan is positioned in the factory shroud ( unless you know for sure it is at it's factory correct placement.
One thing is for sure- you will get this sorted out with advice from here(y).
 

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66 Chevy II, 871 blown 355
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Wow, this is GREAT information, thank you so much for taking the time to post this. So in your opinion, do you favor the bypass holes ? Also should there be 1 hole or 2 ?
I have two in mine but as I mentioned it will have a hard time heating up in cold weather so if I replace the thermostat I will go with one next time.
 

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Measuring temp on the cylinder head. I thought a lot about drilling a bypass hole in my new thermostat but decided against it so no.
I would measure the temperature at the water outlet of the manifold. This is a truer reading of the average coolant temperature.
I would also drill a 1/8" hole in the lip of the thermostat. This will allow coolant to circulate around the thermostat and allow it to open before the temperature goes way up.
 

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So I have an odd thing going on with my 72. (383 stroker 700R4) Every time I take the car out, the temperature initially climbs to 220 + for not even 30 seconds and then cools down over the next 5 minutes or so and then settles in around 185 / 195, it will then run around 190 forever or until I shut the car off and it cools completely. I have a Robert Shaw 180 degree thermostat (which I tested in a pot of hot water, it does open @ 180) , factory fan shroud, factory radiator, 7 blade clutch fan, Auto meter water temp gauge. I have burped the system with the funnel kit 2x and have an overflow tank, the car does dump some antifreeze in and out of the overflow tank every time I drive it.

Any idea why the thing spikes so high initially? Is this something I need to be concerned about ? I have researched this online a ton, but I just can't find anyone who is experiencing the same type of scenario. I'm new on Steves Nova ( been lurking for years ) so I think this may be where I can get some solid advice.

My one car buddy says to not worry about it, just not sure.

Thanks in advance - Jay.
When you burp it raise your front end.
 
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