Okay - so I am having the same problem as the poster on Sept 7 for 'Engine Overheating'. I just bought a 1965 Plymouth Valiant convertible. I had the radiator overflow while sitting in traffic on a 75 degree day. I replaced the radiator cap that was worn with a new one rated at 13. I drove the car on the freeway for about 6 miles and the temp gage went up to Hot. I pulled into a service station to let it cool and the radiator was not overflowing or steaming but was hot. I then decided to take the car and have the radiator flushed and a new thermostat installed (Stant rated at 180). The guy at the radiator shop was great and was explaining what he was doing while checking the radiator. He noticed the vents inside the radiator were clogged and recommended they be cleaned out. He removed the radiator hose from the thermostat housing and same as the other person's post there was NO THERMOSTAT installed. He and I also noticed brown goop in the thermostat housing and the breather cap on top of the engine was completely clogged with same brown goop. He used an airhose to blow out the breather cap and hose and more brown goop came out. He said there may be water in the engine and he didn't want to charge me for the radiator maintenance and I should have the engine checked first. The oil on the dipstick looks clean. I get good compression and cannot see any leaks around the engine. Also, the sensor for the console temp gage has no wire coming out it so that tells me it not even hooked up. You will have to excuse my non-mechanic explanation of things. I am learning as I go and it has been a very bumpy road so far! Does anyone have any ideas what may be going on in the engine?

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1965 Plymouth Valiant Signet 200 Convertible

Welcome on the board.

Are you completely sure it was the same brown goop? The breather cap will tend to accumulate brown goop if its cleaning and maintenance is left undone for years (or decades); that's oil plus dust making that goop. The brown goop in the cooling system is usually rust-based. If the oil looks clean (and not buttery) on the dipstick, probably water is not getting into the oil.

If your temperature sender is not hooked up, that suggests its wire is dangling somewhere, and may well be shorted to ground, perhaps intermittently. If that is the case, then the temp gauge will read "hot" whenever the wire touches ground. You may not actually have an overheating problem, or at least not one as severe as the gauge is suggesting.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks SlantSixDan for your response! I will take some photos and post them for you and all to see. I will try to look for more 'goop' too and take a photo. I will also try to get 'Miss Varla Valiant' to the Slant 6 meet up on Sunday in Redwood City if she doesn't overheat on me.

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1965 Plymouth Valiant Signet 200 Convertible

Found the dangling wire and I will solder it back together and wrap it up real good. took some photos but have to figure out how to post to the message board. Thanks SlantSixDan!

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1965 Plymouth Valiant Signet 200 Convertible