running hot and erratic temp. gauge

[yuke]

My 300 SD was running at a constant 100 c. I took the thermostat out and tested it which seemed to be opening fully. Ran it w/o thermostat and seemed to run too cool not reacning 80c which Im told is s.o.t. So I drilled 3 holes in the outer ring of tstat to get more flow thru radiator and at 1st seemed fine never getting above 80c but on a long road trip after 2hrs. highway speeds my temp gauge started to rise above 100 c and then erattically bounce around 100 and above but never in the red zone. I will change the stat out with a 160 one when I get home but wondering why my temp. Gauge was fluttering. Any one else have a problem to what I described. I hope my problem is in thermost as trying to avoid pulling radiator and having it flushed and cleaned. I got the idea for drilling the holes from a diesel giant writeup he uses one with 2 holes in winter and 5 holes in summer I went in the middle with 3 holes as a test I might go to 5 holes but know it will give me longer warmup times and then be too cool for winter.

[cooljjay]

I wouldn't drill holes in the thermostat.....that is a totally band aid fix.....

First you should see if your temp gauge is even working right, by using a inferred gun to check the temp of the system. Then move on to the other things that may cause a spike in temperature, bad fan clutch, low coolant, wrong coolant, bad cap, bad radiator....etc....even by putting in a high temp thermostat....you are simply macking the real problem

[yuke]

Thanks for the response cooljay I am going to look at it closer when I get back from my road trip. Do you really think a bad rad. cap could make it overheat? I will put a new themostat in and see what happens. Oh by the way I liked how you fixed your oil cooler hoses also fixed mine the same way working out real well.

[rscurtis]

The radiator cap has nothing to do with temperature, it merely increases the boiling point with the use of pressure. A lower-temperature thermostat won't help either if the cooling system is working at maximum capacity. Don't rule out an erratic sender or a tired radiator.

[tangofox007]

Originally Posted by yuke

...but wondering why my temp. Gauge was fluttering.

Checking for a tight, clean connection at the sender would be a good place to start in resolving that issue.

Originally Posted by yuke

I will change the stat out with a 160 one when I get home...

That's a alot like fixing a leaking roof by using a bigger bucket.