Themostat question-
Thread Starter
Burning Brakes
Joined: Feb 2006
Posts: 1,223
Likes: 4
From: Regina Saskatchewan
Themostat question-
I've installed 2 manual shut-off valves to the heater core. When I shut them off with hot weather , my temp. gauge will climb to 210 , sit there for about 5 mins and then drop to 180. 5 mins at 180 then climb to 210. And so on and so on. I 've pulled out the thermostat and put in a new 165 thermostat. Same thing. 5 mins at the low temp and then it jumps suddenly to 210 for 5 mins. I put the 180 back in - back to the same thing. Now if I open the 2 manual valves ,temps stay at 180. (or 165) Anyone have a clue whats going on. Could I have 2 brand new thermostats that are crap. Is the engine producing that much heat that it needs the heater core 'in addition' to the rad to keep things in the lower range? Over all the engine is pretty mild. Maybe 300hp? I've always purchased cheaper thermostats , don't really believe there is much difference. Is there? Should I spend the extra $3 and get the more expensive thermostat? 
Or is there something else going on? Do I need to install a bypass before the shutoff valves?
Or is there something else going on? Do I need to install a bypass before the shutoff valves?
Instructor
Joined: Jun 2007
Posts: 179
Likes: 0
From: Guntersville Alabama
Don't believe your problem is with your stat's. Changing to a lower temp Thermostat only means the thermostat opens sooner, once its open, it's open. Easy to check how well a thermostat is working and at what temp it is really opening at. Thermometer, big old pot of water, kitchen stove. Start heating the water and dump the stat into the water and watch your thermometer, take note of what temp the stat opens and if it is opening all the way.
The question asked "Were is your temp sender?" Is a good one. You will get different temp readings from different locations. I have a pretty Hot 434 SB in my 57 Chevy, last summer after doing some work it was running pretty hot, it would get to 230 degrees and just want to stay there. I did everything known to man trying to figure that one out. I finally starting checking different temp sender locations, and at one time I had temp senders in three different locations and three guages as well. Results from that little experament were very interesting to say the least.
Roland
The question asked "Were is your temp sender?" Is a good one. You will get different temp readings from different locations. I have a pretty Hot 434 SB in my 57 Chevy, last summer after doing some work it was running pretty hot, it would get to 230 degrees and just want to stay there. I did everything known to man trying to figure that one out. I finally starting checking different temp sender locations, and at one time I had temp senders in three different locations and three guages as well. Results from that little experament were very interesting to say the least.
Roland
Instructor
Joined: Jul 2007
Posts: 167
Likes: 0
From: Sheboygan Wisconsin
It didn't do it before the shut-off valves were installed, right. It's the location of the valves. And you should only need one shut-off. Keep the valve as close to the heater core as possible. Do not interupt the coolant flow through the motor.
Racer
Joined: Nov 2006
Posts: 435
Likes: 7
From: Wake Forest NC
Always check the stat as described in the post above. Spend the extra $$ for a good thermostat. After visiting three different auto parts stores, I've yet to find a stat that works for my son's car; either they're mechanically stuck, or the thermal element doesn't cause them to open. Couldn't find the smilie, but give you one guess where they're made...
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Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Hi
The SB motors do not have the water bypass hose from the pump to the intake like the BB have. Therefore if you close off the heater which is acting as a bypass , you stop any water flow in the engine as long as the thermostat is closed. This provides hot spots in the engine, heads.
If you keep the heater water passage open, water will flow throught he engine and avoid this hot spots.
Hence, what you need is a water flow passage as long as the thermostat is closed. Drilling a couple of small holes into the thermostat flat ring will provide a bit of flow without sacrifying the thermostat's operation.
Like mentioned, BB have an aditional hose from the pump at 6 o,clock position to the intake that allows water flow and avoids this hot spots.
Rgds, Günther
The SB motors do not have the water bypass hose from the pump to the intake like the BB have. Therefore if you close off the heater which is acting as a bypass , you stop any water flow in the engine as long as the thermostat is closed. This provides hot spots in the engine, heads.
If you keep the heater water passage open, water will flow throught he engine and avoid this hot spots.
Hence, what you need is a water flow passage as long as the thermostat is closed. Drilling a couple of small holes into the thermostat flat ring will provide a bit of flow without sacrifying the thermostat's operation.
Like mentioned, BB have an aditional hose from the pump at 6 o,clock position to the intake that allows water flow and avoids this hot spots.
Rgds, Günther
Last edited by WESCH; Jan 1, 2011 at 10:53 PM. Reason: typing errors
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
It sounds like you just have air pockets.
How many miles have you run it after filling?
It can take several complete heat/cool cycles to purge the system.
The sbc has an internal bypass on the pass side of the pump mount. It can be blocked off or some aftermarket pumps like the Stewart stage2 I use has no provision for it. Shouldn't make a difference either way if you have at least one bleed hole in the tstat.
I run with no internal bypass and the heater ports in the pump and manifold plugged and a RS tstat with the three holes, with absolutely no issues.
Almost all tstats have an air bleed for filling, but it is so tiny that it takes a long time to bleed out and people don't wait long enough when filling. Drilling one small hole will help a lot for filling.
You can also loosen the heater hose from the manifold when running (not when pressurized) to purge any air.
Also chck how clean your system is, a dirty one can cause all sorts of symptoms. Best is to remove a lower block plug.
How many miles have you run it after filling?
It can take several complete heat/cool cycles to purge the system.
The sbc has an internal bypass on the pass side of the pump mount. It can be blocked off or some aftermarket pumps like the Stewart stage2 I use has no provision for it. Shouldn't make a difference either way if you have at least one bleed hole in the tstat.
I run with no internal bypass and the heater ports in the pump and manifold plugged and a RS tstat with the three holes, with absolutely no issues.
Almost all tstats have an air bleed for filling, but it is so tiny that it takes a long time to bleed out and people don't wait long enough when filling. Drilling one small hole will help a lot for filling.
You can also loosen the heater hose from the manifold when running (not when pressurized) to purge any air.
Also chck how clean your system is, a dirty one can cause all sorts of symptoms. Best is to remove a lower block plug.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Hi
The SB motors do not have the water bypass hose from the pump to the intake like the BB have. Therefore if you close off the heater which is acting as a bypass , you stop any water flow in the engine as long as the thermostat is closed. This provides hot spots in the engine, heads.
The SB motors do not have the water bypass hose from the pump to the intake like the BB have. Therefore if you close off the heater which is acting as a bypass , you stop any water flow in the engine as long as the thermostat is closed. This provides hot spots in the engine, heads.