TheSamba.com :: View topic - What is ideal engine oil temp and where to measure it?

Sat Jun 06, 2015 4:14 am

The engine that came with my sandrail sadly had the stock thermostat and flaps taken out of it (Why do people do that!!?) and It looks like it costs about 2-300 bucks that I don't have right now to restore them.

I do have a digital oil temp gauge of unknown quality and I have a candy thermometer that I can stick down the dipstick hole.

I've read that oil temp should be between about 180º and 220º but oil temp measured where? My oil temp sender is screwed into a T fitting with the low oil sensor and reads about 30º lower than thermometer down the dipstick hole.

With no flaps in place I find that temp at idle doesn't get above about 120º so I've been partially blocking the blower intake to get higher temps. If I keep it about half covered I seem to get a max temp of about 190º at idle that drops to about 170º when actually driving, but the dipstick temp will be right up at 220º

My question is, which temp should I trust? Do I open up my blower when the digital temp gauge hits 190 or do I let it go up to 220º knowing that the oil pan temp is going to be more like 250º?

Also, instead of partially blocking the blower intake port would I be better off partially blocking the oil cooler? (stock doghouse)

Sat Jun 06, 2015 4:24 am

Yes, 85-100C is a good range, but a sensor off a tee won't have a constant flow of oil over it and will give dodgy readings. Ideally you want to be measuring where the oil is constantly flowing over the sensor, but that can be tricky. Measuring in the sump, assuming the oil is moving around, is not a bad compromise, but you need to be aware that a sensor in the oil drain plug is in a pretty hazardous location. Sensors in the relief or bypass plug locations give impressive, but often meaningless results (again because oil is not constantly passing over them.)

Sat Jun 06, 2015 4:43 am

You measure oil wherever it is hottest. Trust the oil temp in the dip stick.

Normal oil temps are 210*-220*F and perfectly save. DO NOT worry until you see above 230* stop driving if you see above 235*-240*. DO not confuse normal 180* water temps of a water cooled engine with normal oil temps. 180*F oil temp are too cold. Oil must get hot enough to boil out acids and other water condensation. If you don't believe me then ask the oil companies directly how to use their products.

Blocking off the fan air intake is a bad idea. You are robbing cooling air the also cools the heads.

Sat Jun 06, 2015 12:51 pm

Quote: If you don't believe me then ask the oil companies directly how to use their products.

Oh, I believe you. If it didn't I wouldn't be worried at all (like whoever put together my engine) and would just let it run wide open all the time.

Quote: Blocking off the fan air intake is a bad idea. You are robbing cooling air the also cools the heads.

My theory was that since the stock thermostat flaps controlled temperature that way it would be a safe thing to do as long as I had a way to monitor oil temp so I would know if I had the air flow blocked too much.

But, now that I think of it there probably isn't a very strong correlation between cylinder temps and oil temp since the cylinders are 'dry' save for what gets splashed on the backside of the piston and could probably get crazy hot without heating the oil very much.

Now, obviously in an ideal world I would have thermostat flaps, but since this isn't that world would you say that its more important to have hot oil or hot heads? Would a reasonable system be to partially block the oil cooler to control oil temp and leave the head air flow on full blast?

Sat Jun 06, 2015 1:21 pm

Keep hunting for flaps a d thermostat ... The number of engines in the USA without flaps you would expect there to be hundreds of junk boxes all across California with flaps and thermostat sitting in them.

If you block the fan off you also block the oil cooler whick increases the risk of forgetting to uncover it and then overheating.

The same engine in a bus may well run at 250F on a hard freeway drive and panic sets in at 260F .... dipstick oil temperature with 210 to 220 degrees being normal. My bus engine survived 500 mile daily runs with oil at 240-250F and lasted 40000 miles before I rebuilt it because of oval crankshaft dowel holes.

I now have an external oil cooler with a 180F oil stat in a sandwich plate fitted for a long drive south in France and the oil now has difficulty reaching 220F. I have gone back to 20/50 oil to get it to run hotter.

Sat Jun 06, 2015 2:54 pm

what the other posters have said.

our bus reads 180F in the sump around town. On the highway it is a function of load and ambient temp. Your sandrail is light and unless you are full power racing for an extended period I would not expect to see it about 210 F to 220 F.

The question where to put the sender cannot be answered in less than a discussion and with much more information needed. There are two questions that need to be asked of any oil - (1) what temperature does it begin to lose lubrication abilities (2) what temperature does it start to degrade permanently.

If you measure it in the sump you are measuring it before the oil pump picks it up. If you measure it after it leaves the oil cooler you will know what temp the oil is being delivered to the oil galleries, and if you measure it somewhere else in the case you may be measuring case temperature. On some engines, like my bus engine, part of the oil recirculates to the pump after it has cleared the oil cooler. This may lower temperature going to the bearings but it does nothing for oil spraying off the piston skirts to cool them and then dropping back to the sump along with the oil coming back off the heads and cylinder walls. We therefore chose to monitor the sump because on our engine that is where the oil is hottest. Your oil pressure gauge will also tell you a lot about how hot the oil is by what pressure the engine is holding.

In the image below, if you follow the dotted green line, you will see the path some of the oil takes on a late T4 case where excess cooled oil is bled back to the pump. Questions like this are hard to answer without much more information so generally my answer would be at the wet sump. If you were a Porsche with a large dry sump my answer would probably be at the bearings.

Sat Jun 06, 2015 3:37 pm

if your blocking the fan inlet (I do NOT recommend doing this) you best get some head temperature gauges. The heads will heat up much faster than the oil, you may have dangerously high head temps with moderate oil temps. don't depend on a high oil temp to warn you that the heads are too hot.

search the want ads and get the correct thermostat set up, do not cover the fan inlet unless you are monitoring head temperatures!!!!!!

180F is a good cool oil temp,( Measured in sump) you don't need boiling temp (water 212F) to remove water from the oil, water will evaporate out at lower temperatures than 212F and figure the sump oil temp (one of the most frequent measurement places on our motors) is NOT the highest temp the oil sees, the thin film of oil flowing over a very hot cylinder head is much hotter than the oil in the sump.

On some of my stock VW's it is difficult to exceed 180F some times for oil temp (sump), yet I don't worry about being too cold. If I pull hard or it is a hot day I see 220F in my Bug. (stock 1600 DP)

Sat Jun 06, 2015 4:56 pm

Thanks for the advice. I've never blocked the fan completely, just restricted it since that is easy and seems to be essentially how the thermostat flaps work. I agree with the point about oil temps not giving much info about cylinder head temps, which are what control the thermostat flaps if I understand correctly. (Radiative and convection inside the heaterbox working on the actuator)

I will keep looking for some affordable thermostat parts.

Knowing now that the oil sump is a good place to check oil temps My next experiment is to figure out how exactly sump temp relates to my T temp gauge since its not really practical to put in an temp sender in the bottom of my oil pan. (Unless I tapped a hole in the side of it? hmmm)

Knowing that my rail will probably run cool anyway because of its light load perhaps its fine the way it is given that my temp gauge seems to run about 30 low from sump temp and my gauge usually runs 50-60C with the fan wide open which could mean my actual temp is pretty close to 180º

What about leaving the heads in full blast and restricting air to the oil cooler?

I also have a scientific grade thermal imaging camera that I can use to look at external heat distribution which may be interesting. I was planning on taking some pictures today but I had the valve covers off last night and one of the gaskets cracked so I'm down until I get a new gasket.

Sat Jun 06, 2015 6:02 pm

Quote: is NOT the highest temp the oil sees, the thin film of oil flowing over a very hot cylinder head is much hotter than the oil in the sump.

You are correct but my concern after mentioning splash off the piston skirts, cylinder walls, and heads, was how he will measure that? What kind of sensor will fit in that thin stream? That ultra hot oil will first collect in the sump and that is the only place he can measure that film as close to the moment it was its hottest for which his candy cane sensor (dipstick) is fine. That is my humble opinion, others may feel different.

Sat Jun 06, 2015 11:03 pm

I would point out that VW used to block the fan with the thermostat. The non-fresh air engines had a ring over the fan inlet. When cold it was shoved in all the way and severely restricted air. When warm it functioned as a Venturi ring, and likely improved cooling over nothing at all (VW went started adding a Venturi ring again with the fuel injected late Bugs.)

Sun Jun 07, 2015 1:26 am

Quote: I would point out that VW used to block the fan with the thermostat. The non-fresh air engines had a ring over the fan inlet. When cold it was shoved in all the way and severely restricted air.

I just had a radical idea....

What if I bought one of those Mexican thermostat actuators, mounted it horizontally below the heads on the right side of the engine and hooked it up to a cable or a linkage that opened and closed a disc over the fan inlet? If I used a lever type linkage I could precisely adjust how far it opened the disc so In theory I could calibrate it to any temperature I wanted and the linkage should be easier to fabricate than one to move two sets of flaps.

For that matter......what if I just mounted a generic $10 water cooled thermostat in the the same set up? The open at just about the same exact temp as a VW one and with a linkage I could translate 1/4" of movement on one end into a couple inches on the other which would be all that I needed.

Sun Jun 07, 2015 2:42 am

RE: Where to measure?

With an IR gun; under the distributor, the distributor, the stamped case number (t1 case), the oil drain plug, the valve covers, the heads, the carb(s), the manifold(s), the filter (if there is one) and transmission.

Sun Jun 07, 2015 8:58 pm

Aerindel wrote: Quote: I would point out that VW used to block the fan with the thermostat. The non-fresh air engines had a ring over the fan inlet. When cold it was shoved in all the way and severely restricted air.

I just had a radical idea....

What if I bought one of those Mexican thermostat actuators, mounted it [u]horizontally below the heads on the right side of the engine and hooked it up to a cable or a linkage that opened and closed a disc over the fan inlet? If I used a lever type linkage I could precisely adjust how far it opened the disc so In theory I could calibrate it to any temperature I wanted and the linkage should be easier to fabricate than one to move two sets of flaps.

For that matter......what if I just mounted a generic $10 water cooled thermostat in the the same set up? The open at just about the same exact temp as a VW one and with a linkage I could translate 1/4" of movement on one end into a couple inches on the other which would be all that I needed.

don't over think this, get the right parts, them Mexican thermostat are no good, they can fail leaving the thermostat flaps closed!!!! FRIED MOTOR!!! the bellows type thermostat originally used if it fails will fail OPEN, and allow full cooling.

Your messing with the cooling system, don't rig it like a hillbilly, rig it like a german engineer would and you will be rewarded with long engine life and the upmost in reliability. do it wrong and you can destroy your engine fast!!!! you have no idea what your head temps are, and you can have dangerously high head temps for a long time before the oil gets hot, you over heat the heads and out pops the valve seat!!!!

a quick search of the classified ads finds a supposed complete set up for $150 to $120 including the flaps and springs an pushrod! a single used working GERMAN bellows type thermostat as low as $30! do it right

Remember no Mexican style thermostat, that fail closed when the wax inside them leaks out. it is the hot expanded wax which fights the spring on the thermostat, opening the flaps, note the spring is rigged to close the flaps, the wax leaks and the spring keeps the flaps closed all the time!!!!! the stock bellows type has no spring to pull the flaps closed, rather the bellows is compressed when cold and if the bellows leaks, it expands, allowing the flaps to open, it is a fail safe design.
I'd run no thermostat rather than the Mexican style one, its failure can destroy an engine, not so with the bellows type.

Don't block anything for now, and in the mean time save some bucks for purchase of the correct parts. the correct parts are fool proof and work. want ads have lots of them for sale.

example.....
http://www.thesamba.com/vw/classifieds/detail.php?id=699610 (no affiliation with ad owner)

here is a link to the search I used....
http://www.thesamba.com/vw/classifieds/search.php?...ton=Search

Sun Jun 07, 2015 9:50 pm

I get your point and I basically agree, but I suspect if the thermostat cost as much in proportion to other parts the germans would have used something else. I mean, I could buy a pair of brand new heads for what it would cost for a new german style thermostat and flaps. I'm sure its worth it, don't get me wrong, I have a great appreciation for the stock design but we are running out of certain parts for it and are eventually going to have to figure out new ways of solving the old problems with current production parts. Not saying that I know how to do that but I may give it a shot, I have the tools to measure temps anywhere I need to so I should be able to safely experiment.

Edit:

Quote: a quick search of the classified ads finds a supposed complete set up for $150 to $120 including the flaps and springs an pushrod! a single used working GERMAN bellows type thermostat as low as $30! do it right

Looking at that link I see that its just the flaps and linkages you get for $120, you have to buy a thermostat for another $120

I do get what your saying about the fool proof nature of the german style. I lost a truck engine when a wax thermostat failed and I didn't notice my temp gauge redlining until it was too late.

Hmm...it just frustrates me when everything else on a VW engine is pretty cheap and easy to find new or rebuilt, except for the freaking thermostat system.

Sun Jun 07, 2015 10:25 pm

Aerindel wrote: I get your point and I basically agree, but I suspect if the thermostat cost as much in proportion to other parts the germans would have used something else. I mean, I could buy a pair of brand new heads for what it would cost for a new german style thermostat and flaps. I'm sure its worth it, don't get me wrong, I have a great appreciation for the stock design but we are running out of certain parts for it and are eventually going to have to figure out new ways of solving the old problems with current production parts. Not saying that I know how to do that but I may give it a shot, I have the tools to measure temps anywhere I need to so I should be able to safely experiment.

Edit:

Quote: a quick search of the classified ads finds a supposed complete set up for $150 to $120 including the flaps and springs an pushrod! a single used working GERMAN bellows type thermostat as low as $30! do it right

Looking at that link I see that its just the flaps and linkages you get for $120, you have to buy a thermostat for another $120

I do get what your saying about the fool proof nature of the german style. I lost a truck engine when a wax thermostat failed and I didn't notice my temp gauge redlining until it was too late.

Hmm...it just frustrates me when everything else on a VW engine is pretty cheap and easy to find new or rebuilt, except for the freaking thermostat system.

there is a complete set up, flaps and thermostat currently listed in the classified section for $125 there is a used working (IE non expanded at room temp) thermostat for $30 currently listed for sale. If you need everything, it looks like $125 will do it, if you only need the thermostat then $30 will do it.

sure it is some bucks for the complete set up, but you will never ever need to replace a leaky radiator, or have to replace old coolant hoses on a Bug. it is just one of the expenses you have with a car, the Bug has some unique parts that water cooled cars don't, But the Bug also does not have a lot of parts that water cooled cars have.

it better you run no warm up system than have a system that if it fails will melt the motor. Unless you have a head temp gauge, your playing russian roulette in so far as using a wax type thermostat. also there are USA made bellows reproduction thermostats available new, pricey, but a lot less than the replacement radiator for my 1991 truck that blew out. (plastic side tank blew out) My 1961 Bug has had one thermostats fail in the 35 years I have had it. Not to bad! and the failed thermostat still allowed my engine to receive full cooling. with no radiator to fail, the bug wins!

Sun Jun 07, 2015 10:39 pm

Quote: it better you run no warm up system than have a system that if it fails will melt the motor.

I can't argue with that.

Quote: it is just one of the expenses you have with a car, the Bug has some unique parts that water cooled cars don't, But the Bug also does not have a lot of parts that water cooled cars have.

I guess that is a good way to look at it.

Mon Jun 08, 2015 4:43 am

You guy are over thinking again,OPEN motor compartment in a sand rail
No flaps needed,in a lite ass buggy, been doing this for 30+ yrs ,just take it easy /idel around till warmed up :wink:

Mon Jun 08, 2015 12:24 pm

Quote: You guy are over thinking again,OPEN motor compartment in a sand rail

Its seems to me as though this would mean it would have more problems getting up to temperature than an actual bug, not less and would need the flaps that much more.

Quote: been doing this for 30+ yrs ,just take it easy /idel around till warmed up Wink

So what kind of engine life have you gotten? is it a myth that running cool wears engines out quickly? It would be interesting to hear from someone who has done' it for a while. I've only had this rail drivable for about six months and still have less than 300 miles on it.

Mon Jun 08, 2015 1:30 pm

I use to run with a power pulley and still only managed to get the oil temp 100F over the outside temperature if I tried. In western WA that meant it never got the oil up to 200F and I did have the expected moisture mess inside the filler.

Mon Jun 08, 2015 5:01 pm

T-stat and flaps DO NOT work in a sand car, if you try to use them you will fry your engine