617 turbodiesel.

Previous owner is a family member and swears the T-stat is "not old." Last few weeks the car has seemingly never come up to operating temp. This morning was quite cold (18F) and on my 40-mile drive, temperature gauge never got over 60C.

Heat is marginal in the car but I know the monovalve is bad and I plan to fix that issue this week.

Are there other ways besides the presence (or lack thereof) of cabin heat to tell if I'm looking at a cold-running 617 or just an inaccurate temp gauge? Or would you recommend just replacing the T-stat?

It's either the thermostat or the gauge. Since you describe less than stellar heating I would suspect the thermostat. They do get stuck open. My 300CD was when I bought it and had the same symptoms. A new thermostat solved it and now it has plenty of heat. The part is cheap and it is an easy one to replace...just be sure to get all of the air out of the system when you refill it. There are plenty of threads about that.

Your lack of cabin heat could also be caused by the auxilliary coolant pump being bad. I think that when the monovalves fail they usually fail open causing excessive heat...not sure though. I do know that if the aux coolant pump isn't working it can cause weak cabin heating.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Thermostat. Heat on max temp at full blast should hurt your hands should you dare place them close to the vents, and you should hear the laments of your suffocating passengers

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1985 CA 300D Turbo , 213K mi

it could be new and still bad.

it happens occasionally.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I wouldn't condemn the 'stat just yet. If the engine makes 60C., it's not stuck open.

If you fix your monovalve and get proper heat, the problem is the gauge. If you don't get heat (and you won't get much at 60C.), then I'd look to the thermostat.

If you can borrow an infrared temperature gun, it would provide your answer in about two seconds. The cylinder head typically runs 180-190F.

The records on my car I bought this past July indicated T-Stat work done in May 2006. Well, my car would not get above 60 degrees on a cold day either. So, I checked the t-stat. That so called t-stat work was just a removal of the t-stat and placing the housing back on "sans a t-stat"

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I like that. A new term. I've got a "sans-a-stat" installed on my vehicle.

Thanks! Yeah! With the new "Sans-a-Stat", cold running is virtually guaranteed in cold weather. I wonder how many of those I could sell?

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

If you talk it up properly, you can probably sell a ton of them. The guys who have that "fuel" conditioner that attaches to a fuel line and breaks up the fuel molecules are probably retired by now...............

You got that right. I saw the "Fuel Master" magnet on the Harbor Freight catalog. That all rates up there with the "Fuel Pills", which was just brown colored mothballs, and Diesel Secret Energy. The fuel pill people got shut down, luckily.

I have an idea...You make up a Stainless Steel "Sans-a-Stat" gasket that replaces "the old, worn out, out of date" T-stat housing gasket, and we can supply it to Lovecraft, guaranteeing "full coolant flow" to his "maintenance free" WVO filter system. I think $29.99 plus S+H is a fair price...

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

My '84 300D was slow to warm and then never made it to the 80C mark. I pulled the thermostat and found it literally in pieces. With a new one in place, the car warms quickly and the guage is steady at just over 80C. It produces noticeably more power at the higher temp, too, which is nice.

Also, while you're in there, it's not a bad time to change the short coolant hose beneath the thermostat housing.

That sounds like a plan........with proper advertising, we can probably sell about 10,000 of 'em.

Yeah! Lets get a market plan going!

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

hey guys, the thermostat is closed when cold, coolant circulates thru the block, warms engine,thermostat opens,closes port so coolant can now circulate thru the radiator. you remove a thermostat and the engine should run hot because the block port never closes.
correct me if i am wrong
larry perkins lou ky

Yes, Thermostat is closed when the engine is cold, but there in no port that closes when the t-stat opens. There is a bypass port that allows coolant around the t-stat, but if the t-stat remains closed, like when they fail, the bypass port is not big enough to allow full coolant flow, resulting in an overheat. A missing, or failed open t-stat does not allow the engine to warm up to normal operating temp on cold days because the cold coolant in the radiator is in full flow at all times when the engine is running. A cold t-stat blocks this flow until the coolant heats up enough for the t-stat to open.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K