Is it a bad thing if... (1 Viewer)


Jan 5, 2004
Reno NV
Thanks all for the suggestions. I also do not drive it too much in winter months, but if I knew a heater would heat up really well, it might make it a little easier should I have the desire to drive it.
Jun 10, 2017
...the thermostat takes forever to "warm up"? Seems like my 76 FJ40 with 2F rebuild takes a long time before really warming up anything significant. Before the gasket engine refresh I did last summer it had the same thing happening, takes forever to really heat up. Almost to the point you think the gauge doesn't work because it stays on C the whole time. If I'm driving around at higher speeds it will eventually start to creep up a little ways away from C but not even half way to H on the gauge.

Heater is what prompted me to ask this question. When refreshing the motor, I also installed a Vintage Air AC/Heater unit. So winter weather I try turning on the heater but doesn't really blow much heat if any. To be fair it had the same problem before but I don't take it out too often.
Of other note, I never charged the AC unit with R134 because winter was coming and I figured I didn't need to do that, but I don't think that would effect anything.


I use a vintage AC in my 68 with an F engine.

1st to answer your AC charging question....the Vintage AC has a dual pressure switch...low pressure and high pressure (it’s next to the dryer). If there is no charge, switch stays open and compressor won’t engage, overcharge and the compressor kicks off on high pressure (will short cycle, start and stop rapidly). The AC is also part of the defrost...heat and AC are on at the same time to dehumidify the air blowing across the windshield. Personally, I’d charge it....just for the defrost, works really well.

Heat...I think the heater core in the Vintage AC is smaller than the original FJ40 core...just doesn’t put out that foot melting heat that the original units had. I also have a rear heater installed and tee’d in just after the control valve Vintage supplied...and I use the original cable control valve that adjusted the original heater water the rear heater line. The rear heater will melt steel and keeps the interior warmer than the Vintage unit. If you only have the Vintage’s working but but at a lesser capacity than the original.

Engine heat....F engine, at around town speeds (35/40 mph), your temp sensor coming off the back of the head (hottest part of the engine) is seeing only about 180 degrees. That is the same location the heater picks up from. At speed (55/60), you might hit 200 on cold days, 210 on hot days. Water going to the radiator at the thermostat will generally be a few to 10 degrees colder then what the sender is seeing.

Hope this helps.


Mechanically Challenged
Jul 11, 2012
The People's Republik of Maryland
Halfway on my OEM gauge=overheated engine.

My needle usually hangs around 1/4 the way up from the left, that equates to approximately 180F.

God I hope not, my SBC is hooked up to the stock sender and the picture below is pretty much dead on. The SBC sits dead center in winter at and “C” all summer. 210 is hot, but probably not destructively hot from everything I’ve read.

I’ve confirmed the temperatures listed below with an IR thermometer - it’s nice to have an actual numerical point of reference for what the ambiguous hashmarks represent. Halfway between C and D is roughly 220, and where I start to get very nervous. The fourth hashmark is 230ish and much beyond that the coolant boils, aerates, stops cooling and things go south in a hurry.

I can’t remember where this came from or what year it represents but anything in the middle third is supposed to be good.

Bottom line, the first hash mark, in winter, is probably fine. If you don’t have a fan clutch and you’re just constantly pushing air at engine RPM’s, that’s going to slow the warm-up time down, especially if you’re pulling cold air.
Aug 18, 2013
Prescott Valley, AZ
Had exact same issue on my brothers ‘76. Investigated a bit deeper only to find the thermostat was installed upside down, yes gotta love how PO’s “fix” things. Installed properly, problem gone. Actually put a new one in afterwards as was not sure how long the e previous one was in there upside down. 🙄🙄🙄

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