Do synthetic oils run hotter or

[schwartzworld]

am I headed for cooling system trouble?

About a month ago I changed the oil from 15W40 to 5W40 Mobil One Synthetic. At that time the outside temps were in the 40 to 60 degree range. When I had the 15W40 in it, the scangauge showed the water temp going to 193, thermostat opening and the temp settled to 188 to 190 and never much higher. Oil temp is usually 5 to 7 degrees higher. This is based on driving at 65 MPH. Now with the 5W40 and it being 70 to 75 degrees outside, the water temp went up to 200 to 205 and stayed put, never higher. Oil temp was 207 to 210. This was also at 65 MPH.
I checked the coolant level, right where it's supposed to be, system has pressure, no residue around the cap.
Oil level is correct.

SO,
First thought was the oil and it being synthetic, holding heat, doesn't see right.
Then I thought the thermostat was stuck closed. It was replaced a year ago. If it was stuck close wouldn't the temps go even higher?
Then I thought, well, time for coolers? How could this happen with just changing the oil weight?
Then again, could it be normal? I don't think that's my luck.

Help

Fred

[2 stroker]

Fred
Your your temps are fine. I hope when you replace the t/stat it was with a Ford t/stat because when they fail, they fail open.
My deltas run ECT 192-194* EOT 198-200* and the highest that i have seen is ECT 218* EOT 228* pulling a 14k 5er up a 7% grade 6 miles long in 90* weather. These motors like a 5w40 Syn oil
2 stroker

[Term3]

The dealer I go to puts in 5W40 oil year round when you request synthetic.

[schwartzworld]

Originally Posted by 2 stroker

Fred
Your your temps are fine. I hope when you replace the t/stat it was with a Ford t/stat because when they fail, they fail open.
My deltas run ECT 192-194* EOT 198-200* and the highest that i have seen is ECT 218* EOT 228* pulling a 14k 5er up a 7% grade 6 miles long in 90* weather. These motors like a 5w40 Syn oil
2 stroker

Yep, Ford thermostat. One thing I've learned from this forum is to always use Ford parts. Good to know that they fail open.

I guess I'm just confused. I'm used to seeing the stat open and the temp drop a bit. I was surprised to see it keep heading up and stopping.

Thanks for the info

Fred

[PGreenSVT]

That coolant temp seems a bit on the high side to me. I'd change thermostats just to make sure. On a 75* day I wouldn't expect to see ECT's over 200* just putting around empty. For sure it isn't the oil causing it.

[schwartzworld]

Originally Posted by Term3

The dealer I go to puts in 5W40 oil year round when you request synthetic.

Your lucky to have such a good dealer. Mine refused to hear anything about 5W40. They said 15W40 or I could loose warranty coverage. I know, they can't do that but they make life difficult for a diesel owner. I had an independent shop do the Mobile One change for me. I have to say that the truck has never run better. The MPG even went up too.

[schwartzworld]

Originally Posted by PGreenSVT

That coolant temp seems a bit on the high side to me. I'd change thermostats just to make sure. On a 75* day I wouldn't expect to see ECT's over 200* just putting around empty. For sure it isn't the oil causing it.

Here's where I'm concerned and confused. Today it's 40 degrees out (nice how our weather goes from 75 one day to 40 the next). I took the truck out and the thermostat is opening. The temp went to 193, stat opened, temp went to 190 and varied between 190 and 192 while on the freeway at speed of 65 to 70 mph. When I got off the freeway and even stopped, the temp went to 188, I've always seen that, no concern there. Getting back up to speed the temp went back to 190 to 192.

So, why at higher outside temps does the truck run hotter? Am I looking for something that I shouldn't be concerned with? I've read too many posts here about the coolers plugging up and coolant changes.

One last item. When I got home I popped the hood to check the coolant level while the truck was running. It was sitting at the minimum level. When I shut it off it went up to the maximum level. Any issues with that?

Thanks for the help

Fred

[bismic]

Are the vent lines properly hooked up to the degas bottle?

[schwartzworld]

Originally Posted by bismic

Are the vent lines properly hooked up to the degas bottle?

Where are those? I see the lines on top, where are the vent lines?

Thanks

Fred

[Term3]

He means the small diameter hoses that comes out by the EGR cooler and goes to the degas bottle plus the one that comes from the top of the rad to the degas bottle.