'74 2.7 Coupe not getting up to temp
 

Guys, I don't think my '74 is warming up like it should. When I drove it in colder weather several weeks ago here in MI (temps in the 40s and 50s) it barely got up to 130F or so. I drove it last weekend on a 70deg day for probably 45 minutes and the warmest it got was about 160F. I figured on a 70deg day it should be to 180 within 5-10 minutes of driving and hold right around there, right? The car does not have an external oil cooler - just the case-mounted stock cooler.

I suspect the case-mounted oil thermostat has bit the dust, but before I spend $200 on a new one and dive into the "triangle of death" I thought I'd get my suspicions confirmed. Thoughts?

Thanks,
Brian

Check it with a temp gun. Test the sensor in boiling water.

This being my first air-cooled car, I was just checking to see if my assumptions about how long it takes to get to temp were correct before diving in and pulling the t-stat. Besides, if it's stuck open, the boiling water trick won't tell me much, since it will likely be in the open position when I pull it. I can confirm the gauge reading with my infrared temp gun though.

Brian

Stick the t-stat in the fridge or freezer then hot water. My assumption is it doesn't move it is bad.

Be careful tightening thermostat nuts - studs pull out very easily
 

shortly after i installed an '85 carrera fender cooler and lines, i was cruising out to see an old client and pulled out to pass an elderly lady, after shifting into third, my eye was drawn to the movement in the rear view mirror - blue white smoke, lots of it.
I shut it down and coasted to the road side and popped the engine lid - OIL EVERYWHERE, still had a little in the tank, but everything was soaked in oil - The thermostat had popped up out of the block, enough to expose the oil passages.

My assumption is that a prior mechanic had over-tightened the tiny nuts securing the thermostat, pulling the stud threads in the MAGNESIUM case.

This was not a fun or cheap repair. We pulled the engine, stripped it down to the long block and cleaned everything, replaced the clutch disc and wiring harness, (it was almost 50 years old and brittle), Helicoiled the old studs and reassembled/installed the lump.
If you have any doubt about the integrity of the block threads, Helicoil them, and obviously, do not overtighten:-)
New Nylock nuts and a new thermostat "O" ring b good to have on hand too.
chris

You must differ between the sensors and the thermostats!

Nditiz1 told you to check the engine temperature with a infrared heat gut, and crosschecking the temperature sensor for the temp gauge in the dashboard in a can of boiling water to measure it's resistance if it's till working. They just barely go bad over time. The oil thermostat named here is sitting in the right rear wheel housing to enable the external oil cooler in right front fender. Depending on the model year it is a snake oil cooler, later got a pipe radiator lookalike at the SCs, finally the Carreras got a meshed oil cooler, cars with catalysts got an additional blower fan. That fan was engaged when oil temperature was higher than 118°C/ 244°F. The thermostats also go bad over time, even when the car sits for longer time.
When you have driven some miles, stop and touch the right front fender to see if it gets warm or not. It should warm up after 10miles. If not, then the thermostat is dead and requires to be replaced urgently.

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Thomas

Thomas,
My '74 has no external oil cooler. It only has the case-mounted cooler with the case-mounted thermostat. I will compare my infrared temp gun readings with the oil temp gauge this weekend to make sure the reading is correct, but if it is, I have to believe my t-stat must be stuck open.

Brian

Ok, I knewed that some early G body cars didn't had the external oil cooler...

Indeed it would make me wonder if a stuck opened motor oil cooler causes too low temperatures. This seems possible to me only when you live close to the polar circle ...These engines will get temperature for sure when driving..even with a stuck themostat...
To me your temp sensor is in question. You can check the line to the gauge by holding the cable from the sensor at the engine case with ignition on. Then the gauge must show top end temperatures.

Curious about your test results...

Thomas

Engine Thermostat Testing………….
 

Brian,

Without testing the engine cooler thermostat in a water or oil bath, it would be difficult to assess its condition. Best way to test it is heating it in a water/oil bath and observe the slide valve opening versus temperature. Below 180°F, the valve would be CLOSED. And will start to progressively OPEN around 185°F to 205°F. And fully OPEN @ 212°F.

Some defective thermostats will stay close other partially open even @ 212°F (boiling point of water). So test and confirm.

Tony

A little more info...it's in the low 60s here in Michigan today. I took the car out for a drive, including about 10 minutes at 80mph on the highway. Car got up to 180 and stayed there while on the highway. So, I'm betting the gauge reading is accurate and the t-stat is just stuck open. Once I got off the highway and cruised around town, it dropped to about 140-150 and stayed there.

Brian