ARX and engine coolant temperature

[jhenle]

I have just started the rinse cycle after running almost 3000 miles with ARX in the oil. So far so good, but I have a question.

The engine is a VW 2.0L (Jetta, '98) with 142000 miles on it. Runs great, doesn't burn oil, oil comes out pretty clean every 4-5000 miles etc. I decided to do an ARX cleaning though. The oil from the cleaning phase came out very dark, and I just did the change yesterday for the rinse using Mobil Clean 5000 (same as first phase).

Today I took it for a 200-mile drive, all highway speeds 65-70mph. I noticed that throughout the whole drive, the engine coolant temperature would stay unusually low, at 160-170 degrees vs. the usual 180-190 degrees. This is a drive that I take every week, same conditions, and I know my car very well including temperatures etc. I have never seen the coolant temp stay so low for such a long time. The levels of all fluids are OK, the engine runs as usual ( like buttah) and there was nothing else unusual.

Could ARX in the rinse phase do that? And how?

 

[eoghan]

I have not used auto rx so you can dismiss my musings, but I would reason if the stuff is doing what it is supposed to do "cleaning out deposits" then one could conclude then that the oil is getting to parts that it was not getting to before and cooling them,, also the deposits would "hold" heat in the engine also because the oil was not able to reach and cool the parts like it is supposed to do.

Oil does not just lubricate it also cools the engine!!!

 

[Gary Allan]

You probably have an oil:coolant heat exchanger. While your thermostat should be holding setpoint temp, if there was an insulating layer on some surfaces that was removed, you could be sending some heat out a whole new door.

I'd check your thermostat if you can't reach normalized coolant temp.

 

[duaneb9729]

I noticed the same thing with my '97 jetta with a 2.0

 

[mechtech2]

Probably a coincidence.
You have a thermostat and the heat exchanger won't affect the running temp. It just helps heat/cool the oil , as I understand it.
Your thermostat should be replaced. Check it? It's a waste of your time. When it's out, replace it with a good quality one.

Your coolant temps seem too cool for good street efficiency to me anyway. Fine for racing or track use, but not for gas economy at cruise.

 

[Gary Allan]

The heat exchanger won't alter your coolant temp. It may alter when it reaches it withing certain limits. For example, while I'm at/near 195F very quickly, I don't exceed it for the same 12miles/20 minutes that's considered the normal warm up period. Now a VW with aluminum head will be shedding more heat sooner ..so the both should heat quicker (the oil lagging a bit).

..but under sustained operation the coolant temp should be normalized.

btw- when I took true readings on my 195F stat'd Mitsubishi, the actual operational temp varied from 180-185F as seen by the temp sensor. It never reached 195F.

 

[jhenle]

Well today after doing some driving around town, stop-n-go, I did reach the normal temperatures rather quickly. But with the slightest bit of highway driving the temp drops by 10 degrees or more. It's crazy.

 

[Gary Allan]

Not that this is necessarily the case, but as was suggested,that would be a symptom of a partially opened thermostat. It's fine under stop and go, but once the coolant volume and cooler air across the rad ..

I would be happier if it was on the upside by a tick or two around town (fan normally cycling) and normal on the highway. Then again, this may really be what's going on. The gauge may be off just a bit.

 

[BearZDefect]

If this is new then I think the thermostat isn't closing properly. Over the summer you didn't notice it, but now that the air is cold, cruising at moderate speed overcools the engine significantly.

If you can, change that thermostat before the real winter cold sets in.

 

[JMJNet]

It is a 98, t-stat can be bad at that age. Heck, anything can go bad after more than 10 years. Things don't last forever????