Old diesel operating temp quarrel?

[Alex_V]

I'm on several forums and FB pages for the 70's and 80's Mercedes, which primarily focuses on the W123 chassis and IDI diesel/turbo diesel engines. In a discussion about cooling system problems, several individuals are putting forth they believe the cars are designed for prolonged operation in the 100-110C range even though all the cars have 80C thermostats, stating that the red mark on the temp gauge isn't until 120C.

Having spent plenty of time in various cars using iron head/block gas engines that use a 190-195 thermostat and gauges that don't read red until around 260, I know iron engines can generally take a lot of heat abuse and survive unchanged. However, I don't see how it's desirable to continually run an engine, regulated at 176F (80C), up in the 230 degree range. Can anyone shed a more scientific/learned light on the matter?

 

[bullwinkle]

When I had my '82 300D turbo diesel, it ran better, had more power, and got better mileage with the higher temp thermostat (believe it was 95C) than with a lower temp tnermostat (80C). The 6.2 GMC IDI and 7.3 IDI NA diesels in my sig also make more power when fully warmed up, both of them have higher temp thermostats in them. From my (admittedly limited) all cast iron MB engine experience-they seem to be pretty darn hard to kill from overheating. I've even heard anecdotal evidence of old MB diesels running with no water pump belt, just the air-to-air oil cooler, running decent highway distances without self destructing (not that I would recommend it)!

 

[bullwinkle]

I've also read a few articles on the 6.2/6.5 GM diesel engines that indicate that running a 180F thermostat with a standard fan clutch and fan can actually shorten head & head gasket life (this is from Kennedy Diesel) because the wide spread between the 210F fan clutch engagement and 180F 'stat temp is hard on the engine. Not that a 6.2 (or ESPECIALLY a 6.5) needs much excuse to blow up when worked hard anyway (unlike an all cast iron MB diesel).

 

[Trav]

All I can tell you is I drove my old 1980 59 HP 200D 600km foot to the floor all the way twice every weekend (there and back) and it usually stayed at around 90-95c (depending on ambient temp) as shown on an aftermarket properly calibrated gauge.
Oil used was Euro Castrol Edge 0w30 A3/B4 which made a difference in top end, good for an extra 8-10kmh vs 15w40 HDEO.

 

[E150GT]

90C
That’s what all three of my OM617 ran at with stock thermostats

 

[joegreen]

I haven't driven my 84 300d in years but I remember it did not run much higher than 80c that's with a new radiator, new oem thermostat, and a citric acid flush.

 

[BrocLuno]

Coming from the big truck world, balancing temp is one of the first things done to get the best from the engine and the fuel mileage. But we ran pretty tight spreads on block Stat and radiator louvers... 190 to 195*F on older engines and their internal thermostats and 200*F to 205* on the radiator louvers (which actually control the running temp).

But we never exceeded boiling temp because any slight leak or a blown hose would blow out all the coolant in a heart beat, and you need time to get a rig off the road safely, especially climbing a grade at slow speed ... So we just pushed it a bit

If I was building a race motor, I'd push it hard. Heat is power in a diesel

 

[BMWTurboDzl]

My two cents:

IF, and this is a big IF, emissions standards were being put in place with regards to NOX the lower temp thermostat might be a plausible response as part of an overall strategy of reducing combustion temps (along with EGR).

Lower combustion temps = lower NOX emissions.

 

[Trav]

Originally Posted By: joegreen
I haven't driven my 84 300d in years but I remember it did not run much higher than 80c that's with a new radiator, new oem thermostat, and a citric acid flush.


Mine neither driving US speed limits on secondary roads. Wide open for the most of 6 hours tends to warm them up a bit but not to boiling (100c) unless something is wrong with the cooling system.

 

[eljefino]

My 83 300D runs at 80-85C and loves it.

Thin oil helps the turbo spool up faster. IMO stuff like keeping the ALDA hoses clear and the valves adjusted do more for keeping these in tune.