temp gauge fluctuations

[plowking35]

I have been experiencing fluctuations with my temp gauge this week. I have been losing coolant since late last fall, not a lot, but enough to cause the low coolant light to come on about every 2 weeks if left unchecked. I cant see where coolant is leaking, so that worries me. The temp will stay at 195 till I come off an off ramp. Then it will go up to 210, but as soon as I accelerate, it will go back to normal. The low coolant light also only stays on till the temp gets around 180, and then it goes off. Any ideas?
Dino

[More Power]

The coolant level may be low enough that a slug of air momentarily makes its way to the temp sender, which then reports an incorrect temp.

In any event, I suspect once you repair the problem causing the coolant loss, your erratic temp readings will disappear as well.

Carefully examine all areas of the head gasket joint between the heads & block, water pump weep hole, all hoses and related fittings to determine if a slow coolant leak exists. Coolant will evaporate if the leak is slow enough, and may not cause a drip.

Once a slow leak has been eliminated - If the coolant surge tank isn't overpressurizing, you may have a bad head gasket or cyl head crack that allows coolant to find its way into the exhaust. Be sure to check the oil for evidence of coolant in the oil.

Don't imagine a worst case scenario till you've eliminated the more likely and less costly possibilities.

MP

[plowking35]

The truck has been using about 1 pint of coolant a week since November. Once last week the temp gauge soiked to 230, and then immediately went back down to 195 or so. The temp gauge has always been rock steady at 195, until that spike last week. Now it fluctuates like I reported earlier. The oil is clean, no evidence of coolant. But also no evidence of leakag anywhere. A new duramax may be in the offing, I really dont want to sink alot of money into this engine.
Thanks for your help.
Dino

[ucdavis]

1) A good radiator shop can do a pressurizing test & find the leak. That's the easiest. Look for a shop that does a lot of custom work (hot rods & such).
2) If you are sucking in air, the oxidation in your coolant system will be accelerating. Shouldn't let this last too long.

[plowking35]

The truck is parked until monday when it gets traded for an 04 3500 x cab with LLY duramax and allison. I cant see dumping several thousand into the engine, or even more on a replacement. I can still get good money for it. The dealer has the truck in stock and its exactly what I need for the business, plus 0% and I need another write off. The 6.5 has been very good to me, has never let me down, and even tho it only has 92K on it, it has 100's of more in hours due to snow removal. It has hauled around 10K since day 1, and much more than that during the winter. I think what killed it was towing a 10K backhoe last Sept about 100 miles, I had to pull alot of hills , and she got warm several times, never overheated it, but well over 210 many times.
Good luck to the rest of th 6.5 owners, time for me to head to the duramax side.
Dino

[a5150nut]

plowking35
Congrats on the new truck. If I were you though, I would be looking at exaust temp and boost gages for the new truck. Might prevent towing damage........

[plowking35]

Yes the gauges are the first add ons.
Dino