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GT6 Funny Temperature on GT6

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Saff

Saff

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My '73 GT6 has shown some odd behavior lately. I've had it out for about an hour drive twice in the last week. Each time, the temperature gauge has been rock solid at about 1/2 (that's excellent here in Texas!!), except it jumped to about 3/4 for about 15 seconds. It happened like that on each of these recent drives. Both times, it seems like it happened after significant deceleration (STOP sign, not emergency stopping). Anyone care to venture a guess on what it's trying to tell me? In the part of the country at this time of year, the temperature gauge is the only one that matters on a GT6!!

Thanks.
 
If by 'jumped' you mean it very suddenly moved... I would suspect something electrical rather than a temperature rise.

A fault in the sending unit or the wire lead would seem most likely and easiest to test.
 
Sorry I wasn't very clear in my post. In both cases, it rose and fell smoothly, albeit quickly. It was definitely a damped response - no bouncing around. I suppose it could still be electrical but I think it's something else. Water pump, radiator blockage, ...??? Thanks for the reply.
 
What you are seeing is the plug of hot water generated in your engine under load going through the radiator and then being cooled back to the thermostat temperature. This could also be quite normal since it is returning to normal temperature.

This is also typical if your thermostat is stuck open, or not running with a thermostat, or the temperature range of your thermostat not correct.

Could also indicate that the radiator is starting to plug up or that you do not have good coolant flow for some reason.
Just a few things to check then:

Check that the Thermostat is in place, functioning (opens and closes, you can test by placing it in a pot of water, bring it to boiling and watch it open the add ice and watch it close) and the temperature it operates at that can be monitored with a candy thermometer;
maybe use some good radiator flush and flush the raadiator or take a good look at the core inside the radiator for signs of corrosion and plugging;
Also check your coolant, how old it is, and its proper mix.
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Probably no help. My rangie was reading about 50 degrees above normal; the needle was pointing to the top of the upper normal range. I tested the thermostat as per SBT, replaced the thermostat, waterpump, recored the radiator, flushed the block, checked the fan blade coupler, forced the electric fans on continuous to no effect. I hooked up a known good guage and got same readings. I finally replaced the sending unit. first time i had seen a sending unit go half bad, i had only seen them open or shorted, not out of whack but operating.
 
I know for a fact that my thermostat is not working right because there isn't one. In the Texas summer, any flow restriction is bad so I take it out when the weather changes. Since coolant and core look good and behavior is completely normal at all other times, I'm going to keep an eye on it and go with the "hot plug of water" explanation for now.
 
I seem to remember on another thread (spridget forum) where someone said it was a bad idea to remove the thermostat. The waterpump needs some resistance to operate properly. Maybe if you only removed the spring and plug and used only the mounting flange, or drilled an appropriate number of holes in the mounting flange.
 
Absolutely - running with no thermostat is strictly NG.
If you cannot stand the thought of a thermostat, then buy one and punch out the center. Study up on fluid dynamics and you'll find that with nothing in there the flow is too slow; pinch down the hole and the velocity comes up, which is what you need. BL used to sell competition blanking plates that were nothing more than the outer shell with the center missing.
 
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