My SD runs a little warm on hot days with the ac on and freeway speed about 75 it hovers around 95c. Fan clutch is good ,I removed and cleaned radiator, Flushed cooling system and have a new water pump. It also runs that temp in city driving but never above 95c. Reading some previous posts I see that alot of guys think thats a normal temp on hot days. Diesel Giant offers a way to reduce temps by drilling some holes in the T-stat. What do you guys think of this? I know it will take longer to warm up but I could swap t-stat when weather gets cooler. Thanks for any input.


Jim

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Jim Messina

1983 300 SD
2006 Silverado Z71

In the interest of experimentation being a good thing, I'd say do it. And post your results. You aren't going to hurt the car. Unless you twist off the thermostat housing studs. 95 C with the A/C on in the summertime is well within normal/average.

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1985 300D Gretchen (Astral Silver) 220k
1983 240D 4-speed Evelyn (Orient Red) 203k


TANSTAAFL

You mention that you believe the engine runs warm at 95°C.

What draws you to this conclusion?

The thermostat isn't designed to open fully until it reaches 94°C. and there are tolerances on both the thermostat and the gauge.

If you're not running at 105C. or above, you really don't have a problem worth chasing, IMHO.

My SD will run at 99°C. in heavy traffic with the a/c running...........I'm not modifying anything and it's not going to overheat.

Mine has always run at 100C since acquiring it 7 years ago. Since then;
- Citric acid flush
- new water pump
- 2 new 80C thermostats
- clean rad fins.

Still alway runs at 100C. 2 different hand held laser temp sensors read between 89 and 94 at the engine temp sensor when the dash guage reads 100. So mine reads 5-10C higher. I wouldn't worry about it too much. These are 25 year old vehicles with over 250kmi and approx 10,000 heat cycles.

I should have figured it out because the aux fan only kicks in during hot days, with the AC on and after a long trip.

These motors run more efficiently, and cleaner, between 90-100 anyhow.

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83 300D 328k mi (623) Light Ivory - daily driver
82 300D 166k mi (881) Thisle Green - fixer upper
82 300D 282k mi (473) Champagne - parts

You should never drill holes in the thermostat, fix the problem source instead. The thermostat should never need to be altered if everything is working correctly.

Change the temperature sender in the head, especially if its over 10 years old. If the temp normally hovers around 95c then the sender may have failed and be sending an incorrect measurement to the gauge. Many times it will fail and send a temperature of 60*c when the engine is actually at its proper 80*c but sending a false high is just as possible. You can verify its accuracy with an infrared thermometer too.

Another sign of the senders failure is a jumpy gauge needle.

I figured that I had a problem because it runs at about 83c on days 80f and below. Had a leaky water pump so it needed changing and the radiator was full of dirt, bugs and cottenwood so I wasn't just throwing work and money at it for no reason. I guess I just feel better with the lower operating temp. But if you guys are running at those temps its good enough for me.The temp guage does have a nervous tic once in awhile and I believe its the age of the car so I will change it out.Thanks for the tip Forced. New glow plugs, aux fan, primer pump and a starter also this year and rear brakes this weekend so I am doing well. My list is complete for now. I removed the pin stripe and was really impressed because there was absolutley no fade. I really like it better without the stripe. Spending my first (feel good) money on her right now. Getting her wheeled out by a pro and pretty excited about that. Gentlemen as always your opinion and time is much appreciated.


Jim

__________________
Jim Messina

1983 300 SD
2006 Silverado Z71