Oil tempurature issues or getting faked out?

[geddes66]

OK, I have a 9 year old engine bored and stroked to a 2007 with about 6000 miles on it. It has a type 3 cooling system on it. The oil temp. is running up to and over 125 centigrade. and tends to stay there, not dropping below 120. I checked the oil, in for about 2000 miles, is still very clear, and has not burned smell to it. oil pressure seems a bit low, 2 bar at 3k RPM. Oil pressure gets to 4 bar when cold.

Could the gauge be off, the sensor mismatched? Or is it really running this hot? could the engine be not sending oil through the stock oil cooler? Cylinder head temp gauge has its sensor glued to the wrong part of the head and tells me it is only 150 f. (By the way, does anyone make those under sparkplug sensors to fit the SMALL diameter sparkplugs yet?)
Thanks for all the help in getting my T3/bradley mix back for a 9 year sleep.

[Piledriver]

First: There is nothing special about thermocouples other than the wire they are made from.
(and the readout amp or display required to use them accurately)

Find a loop crimp connect that fits your plugs (12mm ID is a very common size) pull off the plastic bit, tightly twist the stripped ends of the TC wire together, and crimp the connector over the twists--- Instant under the plug thermocouple, just like you can buy.
(use decent ratcheting crimpers for best results, anything else is usually a waste of time if you value reliability)

Second: Its very possible your sensor (or sensors) are lying to you, unless you are using industrial grade bits.(few do)
The common dash filler automotive grade gauges can be off by 20 PSI or 50 degrees F easily.

Bruce2 or Marc noted this is often due to the sensor and heads being mismatched, at least for the electric senders/pressure gauge heads, even if they come in the same box...
Non-cold-point compensated TC gauges (very common) are only accurate if the readout head is at 72F.

They (IIRC) will read high or lower at a ~1:1 ratio depending on the temperature at the "second thermocouple" where the wires connect to the gauge.
A decent TC gauge will need 12v power to work. (EGT gauges are kinda relative anyway so 50F one way or the other is not really a showstopper---oil temp gauges are usually thermistor based and SHOULD be more accurate. Should...)

The typical TC CHT or EGT gauge is powered by the thermocouple itself... and arguable slightly better than nothing.
Again, for EGT, +/- 50F is ~OK, all 4 will read the same offset.

For CHT +/- 50F IS a showstopper, the difference between damaged heads or keep driving without worry..

A cheap mechanical pressure gauge and a long SS thermometer that can drop in where the dipstick goes may save you a lot of worry, work and expense.

Do not permanently install--- keep them in your toolbox, just install and use temporarily to check the accuracy of your dash fillers.
Std off the shelf units are reasonably accurate, at least close enough for a sanity check.

My DVM came with a K type thermocouple, and it is cold point compensated, and reads <1F off from NIST traceable setups I use at work, regardless of outside temps. You can buy dash gauges like that. You tend to get what you pay for.

The late Gene Berg once had a classic rant on his website that explained why you should never use an "automotive" gauge in excruciating detail.
Its one of the few things I agree with him on, at least as far as verify everything before trusting.

Not everything is poo...But a lot of it is. Always double check.

If you KNOW a gauge reads 50 degrees or 20 PSI high at a certain pressure or temp in the dashboard, its still somewhat useful for indication and trending purposes, you will translate it correctly with little though.

I just measure everything with known accurate tools to make sure its running right initially, then the tools go back in the toolbox, and the idiot light and dipstick will tell me ~everything else I need to know.

[geddes66]

Thanks Piledriver. I will do the SS thermometer to check the accuracy of my OTG. I fully agree, once you know the error it is easy to compensate in your head.

Exactly how does the VW choose to send the oil to the cooler or not? I heard it is some spring vs pressure setup and not a true thermostat.

[Piledriver]

Exactly how does the VW choose to send the oil to the cooler or not? I heard it is some spring vs pressure setup and not a true thermostat.

Its a very simple pressure based bypass system, when the oil gets hot, the pressure goes down, below ~40 PSI the bypass is blocked and all the oil is forced through the oil cooler. When the pressure is high, the oil cooler sees the same pressure on both legs, so sees ~no flow to speak of, maybe enough to get warm, but thats about it.

Even simple things can go wrong...worn relief bores and damaged/mal-machined seat for the control piston, restricted bypass to the sump at teh bottom of the bore, cheap oil filters guts blocking the passages etc.

Note that if you have a huge "high performance" oil pump and/or running very thick oil, things... may not go as the German engineers had in mind...but like the factory heat, when everything is fully intact and working properly, it's dead reliable.
More is not always better, particularly if one ignores how the system works.

If the motor is near stock clearances, a detailed stock pump is most appropriate.
(regardless of engine size, the oil pump flow only "sees" the bearing clearances)

Most aftermarket pumps fit poorly and suck air and leak oil internally where they plug in loosely, so their "biggie size" is usually a lame attempt to compensate for lousy QC. There are work-arounds for that stupidity.

There are some excellent oil system diagrams and discussion in the stickies, so I won't beat it to death (any more) here.

I'm far from a "stock" freak, but beyond Bob Hoovers HVX mods, the best oil system for 99% of engines is IMHO more or less stock.
(plus a full flow filter on a T1)

[geddes66]

I changed the oil to 30wt. I will see how the pressure goes. I have a T3 fan so I can't fit the big oil pumps.