..............therefore, not relevant.

If you filled the head, the temperature will not climb to abnormal levels.

Good deal then. I have not had my thermo out since I rebuild my cooling system sometime after I purchased my SD.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Brian,

You were right on! I drove the car 15 miles and found all of the tubes were warm, including those to the auxiliary tank.

My biggest question/concern is that since I changed to Zerex my radiator temperature is close to 100 C with just regular driving. It used to be more like at 80 C. I noticed this change before replacing most of my coolant system (radiator, water pump, gaskets, thermostat, and radiator overflow tank). After replacing all this it is still the case! The system holds pressure well (I tested it up to 14 PSI, which it maintained). Is this problematic and is there any reason why this is happening? I am in central CA along the coast, where the temperature is fairly moderate (15 C or so).

__________________
dannyf
1984 Mercedes 300 SD 214 K miles. Runs on WVO ~ 22 mpg over 8 K on WVO
1997 VW Passat TDI 156 K miles. Uses biodiesel and diesel. ~ 41 mpg
1996 Mercury Villager gasser. ~ 20 mpg

How did you obtain the data on the radiator temperature?

What's the temperature of the coolant in the head (the gauge)?

Did you say you replaced the t stat? If not I would do it. If you did I would suspect the wrong temp stat.

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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.

Sorry for the mistake. It is not the radiator temperature I was referring to, but the standard temperature gauge that is showing 100 C or thereabouts. This is a new therrmostat, but the old one was also showing higher temperatures after I moved to Zerex. Not that I think it is the Zerex, but perhaps something that I did to the system when flushing? I still have the old thermostat. Not sure if its worth draining everything and replacing it to see? Would rather not, but.....

__________________
dannyf
1984 Mercedes 300 SD 214 K miles. Runs on WVO ~ 22 mpg over 8 K on WVO
1997 VW Passat TDI 156 K miles. Uses biodiesel and diesel. ~ 41 mpg
1996 Mercury Villager gasser. ~ 20 mpg

Get one of those infrared temperature guns. I used one to check my cooling system the other day.

Point it at the temperature sensor at the thermostat housing, it should match the gauge.

Mine was at 180*F which matched the gauge reading of 80*C. (close enough)

You can also check the temperature difference of coolant going into the radiator and out.

My problem was a plugged radiator. I had a local shop clean it (it took three times to get it clean) and for $58, it was well woth it. My SDL now runs at 80* on the dot.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

The SD has behaved, sporadically, in similar fashion. No real defined pattern to investigate. I'm hoping it's just residual air in the head that hasn't fully reached the expansion tank.

The SD has not shown the symptom again after about 500 miles of driving.........but, it's also been quite cold........so, I'll need to wait for warmer temps. for a definitive answer.

Drive it for a few weeks and see if this behavior disappears.

Thank you for the replies. I will keep an eye on my temp. gauge over the next few weeks and see if it gets lower. I will also look for the IR temp guns, but, given a new radiator and many other new components, I sure hope nothing's plugged

__________________
dannyf
1984 Mercedes 300 SD 214 K miles. Runs on WVO ~ 22 mpg over 8 K on WVO
1997 VW Passat TDI 156 K miles. Uses biodiesel and diesel. ~ 41 mpg
1996 Mercury Villager gasser. ~ 20 mpg

I drove the Merc today and, sure enough, the temp gauge was high again, it hovers around 100 C with very normal driving in very moderate temperatures. While I do not have an IR temp. gauge, I did feel the tubes leading to my WVO tank. They are hotter than I ever remember them feeling before, as is my WVO tank. Since my WVO tank is in the trunk, the heat seems to be distributed throughout the entire system and it does have me worried, but at this point I trust my temperature gauge and new thermostat. I am hopeful it is a bubble somewhere in the system but I have some trouble believing its just that since it is so hot all the way to my WVO tank in the trunk. Wouldn't an air bubble block heat flow or eventually just go away?

I have been running my system with the cap on tight. Would running it with the radiator cap loosened for a bit change things and better allow excess air to escape? I assume with the system depressurized I would start boiling off fluid if I did that for too long.

Maybe there is some material that got kicked loose somewhere in the system and is blocking something? Again, if that were the case I would not expect it to be so hot all the way back at my WVO tank.

I'll welcome any thoughts while I keep driving and hope it goes away...

__________________
dannyf
1984 Mercedes 300 SD 214 K miles. Runs on WVO ~ 22 mpg over 8 K on WVO
1997 VW Passat TDI 156 K miles. Uses biodiesel and diesel. ~ 41 mpg
1996 Mercury Villager gasser. ~ 20 mpg

I ran mine with the cap loose once and lost about a gallon of coolant in 5 miles.

Excess air will escape with the cap on tight.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Any air that escapes through the radiator cap would have to make its way into the reservoir first, and this would show up as low fluid in the reservoir. That is, air that took up space in the engine has been displaced by coolant from the reservoir and vice versa. Is the level in your reservoir getting any lower?

Running with the cap loose will allow the coolant to boil at lower temps since the pressure in the system will be much lower. Loss of coolant will lead to higher temps. Running system as designed is best. Perhaps sending unit is bad? Not sure how voltage affects temperature indicator, but you might check that as well.

__________________
mjk

'84 300SD 119KMi (Liesl der Diesel)
'84 300D 326KMi when the oil left (former parts car)
'82 300SD 253KMi (new parts car)