Inconsistent 6.9 engine temp?

[diametricalbenz]

I took the 6.9 on a 836 mile trip unfortunately before the gas price decrease and noticed the temperature fluctuates between ~185 (just above the 185)and ~225 (halfway between the white mark and the 250F mark).
Even when it was cool (est 75F) out the temp would rise and then drop but not stay stable even at 60mph. Any ideas about what would cause this?

[magnumrick]

I had a similar situation on my 250c. I replaced the thermostat, cap, and added "WATER WETTER," to the new coolant. It dropped the temp noticably and stabilized it. I believe it is a "solder seal" product.

[250 Coupe]

You may want to check out this thread on the w116 forum, Michael is having the same problem.

Michael

[Emmerich]

I have a 6.9 and a 6.3 and they both act this way. I was worried at first because my Jeep (not really comparable I know) sits on 210, NO MATTER WHAT.

My 6.9 would go up and down depending on car speed. If I stuck around 100, the temp would start to creep up. It never got to the red though, and back around 80 it started to go down a bit, although once hot it took a while to come down fully. The 6.3 acts similiar but to a lesser extent. I once drove about 60 miles through Mississippi doing 110 and it never got to the red, this was in May or June.

I had the radiator recored and they said several tubes were plugged. I cannot see any difference in behavior since I fixed it so either thats the way the car works or my water pump is not putting out as much as it should. I tend to believe the first since the 6.3 acts the same and they are similiar blocks, plus the fact that if I had a bad water pump, it would probably have gone completely south in the 7 years I have owned it.

As long as you are not in the red, I think you are safe. I know one thing, both these engines put out some serious heat. Both trunk floors get HOT after a while from the exhaust.

p.s. I posted an illustrated step by step procedure for the 6.9 radiator removal and installation at www.m-100.info. Its got nice pics and hopefully is helpful.

[diametricalbenz]

Thanks for all the feedback. The car thermostat was changed a few months ago and did help bring the temp down significantly when it nearly overheated in stop and go traffic with a full complement of passengers and luggage to the airport. The water pump is new or at least newer. It's refreshing to know that the problems are common being that the temp fluctuates with the M-100's. I was just getting worried that I would be damaging the head should it have been run hot intermittently throughout the 15 hours or so of running time. And what a grand time it was!

As for the heat the M-100's are great at doing that. It's like a brick oven....or a locomotive fire grate.

Thanks for the link on the radiator removal I will have to read it over this weekend.