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Discussion Starter #1
I recently changed the heater core in my 69 Camaro. The original Harrison developed a leak. Anyway, I have a 400 small block with Trick Flow heads and I have the Autometer temperature sender mounted in the right hand cylinder head. Before the heater core change, the water temperature would jump up to 220-230 or so, then the thermostat would open and bring temps back down to 180-190. It would stay at this temperature until I shut it down.

Now, water temperature slowly creeps up to 180-190. Why would this change? I do believe that the old heater core was partially stopped up. Water was flowing through part of the heater core, not all of it (I think). I never thought that the heater core was an integral part of the cooling system. There are many people that don't run them at all.

Does anyone know why this has suddenly changed? Also, do you think that I have damaged my engine from the high temperatures?

One other thing. I don't know if this is a coincidence or not, but the engine seems to run smoother and a little better now, but that could be attributed to the cooler air last night.
 

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Discussion Starter #2
I dug up an old post that I started when I first put in my gauges. Here is a link http://www.camaros.net/forum/Forum9/HTML/004853.html .

If shooting up to 220-230 or so then going back down when the thermostat opens is normal when the sending unit is in the cylinder head, why would this change when I installed a new heater core?
 

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Cameron, you've answered your own question.

The new core flows better, thus, cooler temp.

The location of the sending unit might produce higher temp readings due to it being located further back in the block farther away from the water pump, maybe by 10 degrees.

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Everett "OBJECTS IN THE MIRROR DISAPPEAR UPON RAPID ACCELERATION"
 

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Discussion Starter #4
I don't think that the flow rate through the heater core has changed that much. Water could flow freely through the old core, but I don't think that water was getting through every passage in the core. That is what raised this question. I have no change in flow rate, but I have a change in the way the engine comes up to operating temperature. The operating temperature itself has not changed, but the way in which the water heats up in the cylinder head has changed. I am not really worried, but I would like to know why.

Also, does anyone else have their temperature sending unit in the cylinder head? If so, how does your engine warm up? Does your temp gauge shoot up to 220-230 or so then cool down to normal operating temps when the thermostat opens or does it steadily go up to normal operating temperatures?
 

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I have the stock gauge and sender in the head and an autometer gauge and sender in the intake manifold. Both are in sync with each other. The factory gauge doesn't spike higher, they just climb and fall together.

You may have had a stuck thermostat or air in the system. The core change may well have made the difference. It's an additional heat exchanger and just because the old one still flowed some I think it wasn't able to exchange the heat as well. In other words the crap that plugged it, insulated the water from the metal of the cooling fins. Same thing can happen to a rad core if internally it gets covered in crap. It still flows but it becomes less efficent in transfering heat...



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...Dennis
"The '69, the '96 our local club"
and the "daily driver"
 

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i recently experienced a similar deal w/ my car, only it was a gradual rise always before, then one day it started spiking as you described. i assumed i had air in the system, and bled it off, only to have it start spiking again. that was just before my 34 year old heater core gave up the ghost on me, dumping its contents on the ground. when i disc. the core and bypassed it w/ a single hose to get it up and running again, it went back to a gradual rise to 180 again. my thoughts on the matter were the old core was sucking air and not allowing the system to operate correctly, untill it fully gave up. it only "spiked" a day or two before it let go, now all is well again. except i have yet to replace the core. thats a winter project. good luck, hope that helps!

[This message has been edited by 68rs406 (edited 10-25-2002).]
 

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I noticed my temp is acting similarly, and it is slowly getting worse. Now it will spike to almost 250 before dropping to 160. I think it must be the heater core from what i am reading. How complicated is the core replacement. I have heard the front fender needs to be pulled to change the core anyone have any thoughts? Would it make sense to put in a big block heater core to leave the option open for later mill swaps?

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69 350 4blt main (383 on the way !) vortec heads, Comp Cam XE268 w/magnum rockers/springs/retainer

New as of 6/1/02:
Baer 13"Tracks front and 12"Touring rear drilled and zinc washed
12:1 quick ratio box

[This message has been edited by dceresa (edited 10-25-2002).]
 

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I the big spike during warm-up then down to norm temps is caused by a sticky thermostat. Its probably just a coincidence that it started working when you changed the heater core. Thermostats are cheap, I'd replace it.
 

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on mine it was an almost new high flow therm., and i still havn't changed my core yet. it could be a coincidence, but its odd to see people having similar things happen with heater core related issues. but, like you said, eric, if the engine starts doing these things and your not sure about the therm., and you know you dont have air in the system, it would be the first thing i did, as well.

[This message has been edited by 68rs406 (edited 10-26-2002).]
 

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Could it be that the tempature spikes are what is causing the heater cores to fail? I agree with Eric that the thermostat is why the tempature spike happens, so if this is the case and you let the temp get to 230-250 range the pressure in the cooling system also rises. The added pressure may be why the heater core fails. Just a thought. That would not explain why after just replacing the core, the temp spike goes away. Did you guys replce the thermpstat too?

Royce
 

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Discussion Starter #12
I did not replace the thermostat when I replaced the heater core. I currently have a 180 degree Robert Shaw thermostat in the engine that I installed about a year ago. Just as a safety precaution, I went and bought a new one today. I have not installed it yet though. I did notice today that my engine was running at about 190 all the time which is about 10 degrees hotter than it usually runs while the car is moving. I am going to replace the thermostat in the next few days. I'll let you guys know if the engine does anything differently.
 

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On the above note: If a thermostat is rated for 180degrees (pick your favorite one) does this mean it is fully open at this temp, or it's just starting to open?
Jeff
Good luck on the heater core problem, think mine is due here shortly too...
 

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<BLOCKQUOTE>quote:</font><HR>Originally posted by JefeOsterhead:
On the above note: If a thermostat is rated for 180degrees (pick your favorite one) does this mean it is fully open at this temp, or it's just starting to open?
Jeff
Good luck on the heater core problem, think mine is due here shortly too...
<HR></BLOCKQUOTE>

The more expensive Robert Shaw's (Mr Gasket I believe) will open completely quicker than say a Stant. Or so the story goes. I have put both types in a pan of water and stuck the pan on the stove to test and both went "POP" when they opened and went completely open. I didn't try to stabilize the water temp at 180 or 185 to see if they partially opened so I can't say for sure. The water temp in the pan was rising and with the meat thermometer it was real close to 180 when they popped open but by the time I turned the stove off the temp was well over 190 and was climbing.

With the RS 180 stat in my 383 the temp will go to just below 185 and drop to just above 175 in less than a minute. I equate that to the stat opening...
 

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Discussion Starter #15
I currently have a Robert Shaw thermostat installed, but it has been in there for over a year. I bought a new one the other day, but I haven't go around to installing it yet. I'll let everyone know the results when I do intall the new one (if I ever get around to it)
 

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The heater core shouldn't make any difference. Some thermostats have a bad habit of spiking before they open up for the first time after setting. I bet you have air in the system. when you replace the thermostat fill the manifold up with water before you put it back together. That should take care of the air lock problem you can also drill an 1/8in hole in the thermostat to let any trapped air out.
 

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To get all the air out of the system I have read... Fill the radiator up most of the way, then with the car running and the rad cap off allow for thermostat to open and top off the rad.
Jeff
 

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I agree Dennis, the Robert Shaws and Mr. Gaskets look like they are sourced from the same tool and parts. Minor differences, but this could be due to sub-parts suppliers.

I use either. Summit has the Mr Gasket and I drill eighth inch holes for all my uses. I think that the Robert Shaws are too leaky (due to the big holes) to warm up adequately.

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See the USA in your CHEVROLET Randy E.
 

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I have Robertshaw #330-180's in both my cars (and have used them in many other cars over the years); both warm up gradually, don't spike, and remain at stable operating temps.

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JohnZ
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Discussion Starter #20
I just changed the thermostat. I installed a 180 degree Robert Shaw (which is what was in it). There is no change. It is still warming up gradually like it should. I don't know what happened, and at this point, I'm not going to worry about it. It warms up like it should and doesn't run too hot. I don't know what was going on before the heater core change, but I am thinking that it may have been an air pocket. All I know is that it is warming up right now.

Thanks,
Cameron
 
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