Oil coolers--What Berg says! m

Dr. Clock and others,

Do you think that large openings in the inner fender panels on both sides just behind the dual air cleaners would have the same effect as an opening behind the rear license plate ? Could place screens to keep debris out. The reason I ask is that my oil temp gauge  goes up to 220-230 F.when I run at 70mph on my 1914 cc non stroker. If I slow down it drops fairly quickly to 200-210. But I don't want to slow down! Would there be different air pressures from the fender openings as opposed to the plate opening? Thanks for replies.

Joel

Joel,

 

I'd love to have somebody try this.

 

I keep thinking that a CB "turbo hat" instead of an air-cleaner, with a 2" take-off going into the wheel-wells, connected to some sort of flat air-box would be worth pursuing. You've got to keep tire-spray out of the engine compartment in the rain, but I can't help but wonder if this isn't the high-pressure zone we're looking for.

 

Do it and report back!

I'm having this done to my IM.

I'm having tubing running up from just in front of the rear wheel wells, so 'clean' air will enter from under the car and funnel up the two tubes and enter the engine compartment beside each air cleaner.

 

I think G.R's observation about keeping water spray out of the engine compartment is valid here: As long as the air 'entrance' is lower than the 'exit' there won't be a problem... Water doesn't run uphill.   A tab-pull lid from a soda can would make a perfect 'off set' spray deflector.

Air will only flow if there is a pressure differential.  In a conventional front-engine car, if you have a sealed engine bay, air coming through the front-mounted radiator will only flow as long as the engine bay remains at low pressure.  However, without any escape route, the engine bay soon fills up with air, until the pressures on both sides of the rad are equal.  At that point, air no longer flows.  Just that simple fact seems utterly amazing to me.

 

When we make "inlets" and outlets" for the engine bay, we think we know the direction air will flow.  Absent the use of a manometer or magnehelic gauge, we're guessing about air flow direction.  Remember that air flows from high to low pressure.  That applies to meteorology as well as aerodynamics.

 

Hood vents in a standard, front-engine sedan are openings designed to exhaust air from the engine bay.  Outside and inside pressures need to be considered prior to effective placement.  Every car has different areas of high and low pressure, both on the outside of the body/hood, and inside the engine compartment.

 

I am removing the entire body of "rear hatch", which is the compartment used as an engine bay in most Speedster replicas.  Only the trunk lid will remain stock, but I am removing the fiberglass under the grill, and replacing it with either a grill or louvers, depending on the results of road tests.  The compartment will be completely open, with only a supporting rack and a heat exchanger/rad.  One of the three Water to Air intercoolers will be placed in the trunk with one or two puller fans on top.  If sufficient air can be evacuated with two rows of louvers, that's what will be used.  If not, a powder coated grill with 70% open area will be used.

 

If you decided to place a 4" air tube running from the engine bay to a wheel well, air would follow pressure, moving the air from high to low pressure.  I don't know enough to predict which direction the air would flow, but one of the gauges mentioned above would tell you which direction so you would at least know what to call the tube: inlet or outlet air.  I would think the engine bay is high pressure, but much of what I have learned seems counter intuitive to a shade tree guy like me.  

 

Engine bays in our replicas with VW a/c engines may have several different air pressures inside, with a large variation, depending on distance to/from the fan, carbs, deck lid, etc.  A scientist would figure out what data needs to be logged, and which tools he needs to measure relevant data: head and oil temps at different engine rpm's, ambient air, grades, etc., which measuring devices to measure pressure differences, then road test to determine the optimum way to reduce under hood temps.  Much of science is a compromise, i.e., the way to cool a drag car doesn't help a rally or road car.  What our group would benefit from is the optimum under hood temperature reduction for a daily driver that sometimes sees track use.   

How about retiring, Stan, and starting a new industry?  Seems to me there's a lot of room for innovation.  

Joel, first of all, are you sure of that gauge calibration? Bring a pot of boiling water out to the car, and after pulling the sender, and adding a ground to the sensor body, immerse the sender and take a reading. Bringing the sensor and gauge inside doesn't seem very practical. Please don't burn yourself! I'd also verify with one of those instant-read meat thermometers.

 

If, in fact, it is accurate, I wouldn't worry about it. If the temp kept climbing at 70 mph, I'd worry. But since it goes up a little and hovers in a slightly elevated temp, no problem, unless that temp is 250 or more. I actually like 200 or so, that way you are 100% sure all the moisture is driven out. My .02.

Air is flowing all the time in the engine compartment. Moving, stopped, whatever. It's being sucked down the carbs or blown out the bottom by the fan. 

 "I would think the engine bay is high pressure, but much of what I have learned seems counter intuitive to a shade tree guy like me."

 

Jim, I thought the engine compartment (with the engine running) is a low pressure area?

I admit I have limited knowledge in this area, but here goes.....

 

1.  engine off-outside engine bay and inside engine bay air pressure is equal

 

2.  engine running (low speed)-draw from fan and carbs creates a low pressure area causing air from the higher pressure area (outside the engine bay) to be drawn into the engine bay.

 

3.  engine running (high speed)-draw from fan and carbs increases dramatically creating a much lower pressure area in the engine compartment and to compensate the pressure difference more air is drawn into the engine compartment.

 

Now comes the problem-if there isn't enough openings to allow enough air into the engine compartment to satisfy the needs of the fan and carbs there will be an 'air deficit' in the engine compartment and bad things, such as overheating, will start to happen.

My mechanic and I are thinking that air will only be drawn up the tubes he's installing  and into the engine compartment when the difference in air pressure becomes great enough.

How well this will work is the question, because I don't know if the space below the car is a high or low pressure area.  I'm thinking it's a low pressure area and if it is there won't be a lot of air flow into the engine compartment, unless there is still a significant difference in 'low' pressure between the underside of the car and the engine compartment.

 

Joel:

 

Before you get lost in these lofty posts of Thermodynamics ( a subject I, admittedly, had to take twice before I passed it) and/or Laminar Flow (a subject I'm thoroughly familiar with), get yourself a dipstick thermometer and "calibrate" your dash gauge with it.  If your gauge is anything like mine, it could be way, way off.  In fact, I reset the operating range on mine just to get the needle to point straight up under "normal" conditions.  That was done with a specific value resistor (found by trial and error) in parallel with the sender.  Once there, I used a dipstick thermometer to find out what was going on and made a couple of small, discreet marks on my gauge glass to tell me where "normal" ended and "worrying" began on the gauge.

 

Danny's idea of using a cup of hot water is good, but it's a single data point and artificial compared to actually running the car and knowing what's going on under different circumstances.

 

Unfortunately, my favorite thermometer once came from Mainely Custom by Design up in Berwick, Maine, but Dave has closed up shop and retired and I don't have a ready replacement for his high quality stuff.  One would think that a meat probe might work in a pinch.  I just measured my "Mainely" dip stick and from the coller that sits on top of the engine dipstick tube to the end of the probe is 6-3/4" exactly.  Get a probe longer than that (preferable with temperature numbers on it rather than "rare ", "medium", etc. and adjustable to calibrate it for 212°F) and put some sort of stop on ot to keep it from going in too far and you should be all set.

 

Anyway, my point is, you may be worrying about a red herring........

    I also have a Mainely Custom thermometer. A fine (although expensive) instrument, that gets hot as a pistol waiting for the needle to slooowly read maximum temperature...gloves, handkerchief or rag is recommended for extracting it from the dip-stick tube.

    Whereas my wife's digital meat thermometer instantaneously reads oil temperature. I was initially skeptical on how accurate a less than five dollar item from WalMart could possibly be...but I compared the two side by side in a cup of boiling water and got the exact same reading!

 

    So, if someone is hankering for an authentic Mainely thermometer give me a 'dialog' and we can hash out purchase price...but bear in mind that it was initially expensive, and now that Mainely Custom is no longer in business, this item could qualify as a 'rare collectable'!!!  

 

 

Just curious about oil temps. I use a Dakota Digital temp, gauge to monitor my CB 2110.  I installed the sender on the engine in the rear oil pressure relief valve with a special purpose fitting for this. My temp. varies from 190 to 215. I have an identical sender tapped into the mini add-on sump. When i use this sender on my gauge, it scares the crap out of me! It goes from 190 to 250. The dilemma is: Is the first one telling me my cooler is doing OK but needs to be bigger to get the second temp.range lower? Or do I even worry about what the second temp.range is after the oil has went thru the engine and done it's job?

 

About negative air pressure. Rusty Smith and i tested our cars inside the engine compartment and found that both of them were giving negative pressure readings.

We used a water manometer and registered 1 to two inches at above 3000 rpm both at hi-idle and on the road. Both of our cars are really sealed up perfectly in the engine compartment so that air can only enter thru the "Hibachi grill" . Rusty's had a slightly higher negative pressure. Upon close inspection we determined that the right and left areas where the air actually enters the engine compartment from the fiberglass "rain guard" attached to the underside of the the engine lid was smaller.

than mine. Not a lot but we both felt that this particular area is barely adequate at best. We opened his engine lid approximately 3 inches and did another hi-idle test at 3000rpm...Voila....no negative pressure!

I too am really curious about the usefulness of those vents in front of the rear wheels being discussed. I've trying to think of a device that could be temporarily attached in the area to measure negative pressure (or positive). Just sticking my manometer tube out there may produce a venturi effect and give false readings. Anyone have any ideas?

Also, once those vents/ports were installed in front of the rear wheels it may totally change the characteristics tested with the manometer originally!

I am really interested in this topic.......Bruce

 

 

 

You may be onto something here, Gordon.

 

I mean, all of those numbers can be confusing and, at the very least, hard to read in a Speedster on the road.

 

My gauge has no markings at all other than two plain little green blocks at both ends.

 

Why not add a few significant marks mid-scale and label them accordingly:

 

 

- piece o' cake

 

- uh-oh

 

- cause for mild worry

 

- start panicking

 

 

Bruce, your temperature differences between the two sending units is startling.  I expected there would be a difference, but not as much as 35 degrees!

Using something like a Mainely dipstick thermometer in conjunction with readings from both sender locations may give you an idea as to which sending unit location is the more accurate.

I am honestly OK with using only the typical VW oil temp sender location, right next to the distributor.  Supposedly, this is the temperature of the oil running through the oil gallery and directly feeding the bearings.  Theoretically, it should be cooler than the sump, because it's coming directly from the oil cooler and ahead of the bearings.  The oil in the sump is after the bearings and splashed down from the crank/rods and bottoms of the pistons and should be hotter.  I'm not surprised at 35°F difference.

 

In this engine design, that is pretty much the only oil temp reading I care about and seems to be the choice of VW/Porsche designers, too.  Keep the bearings within designer-defined operating temps and they will survive - and so should the rest of the engine (Within reason).

 

 

Cylinder Head Temps are a whole different thing, should be monitored differently and mean something different as well.  We're talking just oil temp here.

 

The various oil temp 'ranges' defined by the VW/Porsche designers are important, but due to the aircooled nature of the engine, you have to expect them to swing around a lot during normal operation.  The old rule of thumb is anything under 220°F at the bearings is OK, and anything over 230°F is getting pretty bad - if you're pushing over 240°F stop the engine before the bearings sieze by overheating.

 

So......I use the same oil temp location that the VW/Porsche designers use for the gauge,  and use the best means I have to calibrate that reading on my gauge.  However, that means that I'm using (with a dipstick thermometer) a probe location that is hotter (measures temps on the hot side of the bearing oil flow) than the gauge sender location to calibrate the gauge.  THAT means that, for any temp reading on the gauge, the actual bearing temp will be slightly lower, and that's a GOOD thing.  I'm OK with THAT, too.

 

I also keep it simple on the gauge face, by choosing NOT to have to have a numerical scale on the gauge (almost impossible, given my budget, to make the scale accurate).  I prefer to have a simple bar scale and note, as Mitch alludes, a safe operating range and a "danger zone" and that's it.  

 

I do like Mitch's defined ranges, though.  Thinking seriously of making up some gauge face rub-ons to make it show his ranges.......That should really upset the "Porsche Snobs"!!

 

Carl!  What brand of Walmart meat thermometer are you using?  If it works well and is el cheapo, it should be fine for the rest of us (and I have the same issues with my Mainely Custom dipstick as you've had).

Gordon, I am afairly new member and have been following a number of your responses to various subject matters...I stand in awe with your knowledge as you seem to be a veritable cornucopia of very usable information for us replica guys. I very much appreciate you sharing your knowledge and it makes the MADNESS so much more tolerable! Cheers!

 

Gordon, feel free to use the labels. I won't make any intellectual property claims.

 

Come to think of it, no one has ever claimed I had any intellectual property.

 

 

 

 

Gordon...I tend to agree with you that the oil temp Before it gets to the critical engine parts is most important and keeping that down is paramount. Question: if you install the temp sender in the same outlet that the oil pressure sender is, how do you get the thermocouple bulb of the temp sender to have adequate contact with the oil flow in that galley ? I have seen "tee' fittings etc. but no real effective way to achieve actual bulb contact. Granted...it may, by conduction, be reading the correct heat but maybe with a lag. This is the only reason I chose to install my sender in the rear pressure relief valve plug. I'm a little disappointed in the oil temp's I'm getting with the original oil cooler and an external (72 sq in) cooler and fan in in the L/R fenderwell. Granted...I'm within in std s. even when I'm driving in Hot Calif weather and really stand on it but I don't have a margin of confidence.

What do you think about that DTM Fan Shroud System? I see they are advertising in Hot VW again this month.

No comments/suggestions from anyone on how and where to mount my manometer in front of one of the rear wheels?     I appreciate and enjoy everyone's comments here......Bruce

 

So I'm thinking' to add maybe just one more marking...SHTF now put the fire out!

Bruce, can't you just duct tape the manometer tube to the body for testing?

Dutch wrote: "I stand in awe with your knowledge as you seem to be a veritable cornucopia of very usable information for us replica guys."

 

Got you snickered too, huh?

 

My wife claims that I'm just full of BS.

 

Wives are so practical........

 

This nonsense started out much younger:

 

Bill....Yeah I could but my concerns would be if it turned out to be like a venturi and gave me a negative pressure reading because of the air flowing by it. Sort of like taking an air hose and air nozzle and  blowing at almost a right angle across another hose end. This creates a vacuum in the second hose from the venturi effect. By the way, this is how I get a siphon started to drain the gas out of a tank. Totally tasteless Ha Ha! Anyway I hope you see what I mean. If the tube tip faced up,down, or rearward it could give me these readings. Facing forward it could give me a positive pressure reading due to air velocity. So it's possible in this case that there IS a negative pressure in this area but due to the air going by, this could be nulled out. These are some of my thoughts. i could just go out and try all four positions and see what I get but then that data may be skewed because of the above. I am thinking of some sort of "diffuser" to attach down there in which I could could insert the manometer hose. Does anyone have any suggestions? Do we have any aerodynamic engineers out there? I thought of using two manometers in two different positions and get simultaneous readings as well. I'd like to collect this data on the current car I have because the next one probably will be a wide body and I want to put those ducts in. I think they look so COOL and why not make them functional. Especially since it seem that there is a problem with getting enough air into the engine compartment already. Although I don't have it, that big hole in the firewall in front of the fan is just plain ugly and looks like an after thought to solve a serious problem. After a year of working on my car I am still happy and pleased with what VS delivered to me. EXCEPT...That hole and insufficient sealing at the rear of the engine compartment adjacent to the tail lights. Hot air is sucked up easily there. Both are easily corrected......Bruce

Bruce, I don't think the DTM shroud would have that much impact on oil temperatures.  It would, I think, reduce your cylinder head temperatures.

I had an oil cooler similar to yours and mounted in the same place.  This time around I'm going over the top with two Setrab coolers and fans, mounted in the front of the car.

 

Also, would a air scoop over the hibachi grille help? Maybe facing backwards. Or something like this?

Last weekend I completely sealed my engine bay. Taking it out for a 45 minute run on the freeway on an 82 degree day my dipstick thermometer read 205 degrees.

 

Something interesting that I noticed - When I stopped to check the dipstick temp I noticed the deck lid grill was very cold to the touch. This indicates to me that there is an enormous amount of airflow through the grill and it most likely is not enough.

 

My next test will be propping the deck lid open on an 80 degree day and noting the temp. My guess would be 195 degrees - and if that is the case then I will be cutting the center out of my deck lid and putting a screen there under the grill.

 

Continuing my support of the never ending speedster cooling saga...

Rusty,

Hmmm...Now that's a very, very, interesting observation.

 

You may be on the verge of writing the final chapter on this 'Cooling Saga' 

Carl, how long is the probe on the WM digital?  Thanks, Art

I know this is a well worn subject... My engine tin and seal had many large gaps allowing hot air to be sucked in from the bottom. I fixed all that this last weekend. Up until now I have not been able to drive that car in 80 degree weather. A 45 minute drive would have resulted in 220-225 degree oil temps so it has mostly sat during the summer - which has been... a bummer.

 

I have discussed and tossed around ideas with other members but until I thoroughly sealed my engine bay nothing could really be accurately said. I now have a platform from which I can establish a solid baseline for my engine and I plan on trying some things to share with the rest of you who have a 2110 engine.

 

My goal is to be able to drive in 105 degree weather and the engine temp run in the 215-220 range. Is that possible?

Art:

 

Word has it (from a dialog with Carl) that the Walmart probe is about 6-1/4" long - about 1/2" shorter than a Mainely Dipstick - so he extends it a bit by putting a stop of some sort on the wire at the right length and then pushing probe and wire down into the stick tube to the right depth.  I would suspect that the probe is long enough as-is, but haven't bought one yet.

 

From Carl; The thermometer is TruTemp #3516, and reads from -40 to +302F

Art,

The length of the digital probe is 4 3/4"

The length of the Mainely (specifically for a type1 engine) is 6"

 

I extended the digital probe by tightly coiling a stiff copper wire around it and Gorilla taping the top of the wire (above the oil level) to the probe So it wouldn't, couldn't, slip into the sump...Not very elegant, but it does the job!

Carl, I hope you don't drive with in in...

Heavens NO, Bill...

I don't have ultimate faith in Gorilla Tape!

 

Although I think the Mainely thermometer could possibly replace the dipstick since it has a tight fitting rubber grommet to tightly seal to the tube opening.

...And a sense of humor too As the Aussies would say, Good On Ya Mate!

Hi Rusty - I have a temp issue with my 1915 as well, and would like it to run cooler. Did your engine bay have an opening behind the Dog house to let air in? If so did you seal it up and then it ran cooler? WHere did you get the dipstick thermometer? Thanks!

Rusty are you running an oil cooler on that engine? If so what brand and where is it mounted? Thanks again.

Hi Dutch,

 

My car doesn't have the hole in the firewall like the Vintage cars have. I am currently running an EMPI 96 plate cooler with a stated 1000cfm fan. It's mounted in the rear driver side fender well. I was told that the EMPI cooler that I am running isn't efficient and to buy another higher quality cooler. I bought the dipstick thermometer from Mainley Customs but they are now out of business.

 

Anyone have any suggestions on coolers?

One thing that hasn't been mentioned yet is the type of engine case.  If you have an aluminum case, like I do, your oil temperature will be slightly higher....somewhere in the 10 degree F range.

Cooling these engines can be a real head scratcher sometimes.  When I owned my IM the first time my engine (2110) had a 911 style shroud and inexpensive external oil cooler mounted above the transmission. With this type of shroud the stock oil cooler had to be taken off and the in/out oil passages blocked off.

That means all my engine cooling was handled by one aftermarket oil cooler similar to the one Rusty has installed on his car.

The engine should have overheated while driving on the highway in really hot weather, but it didn't.

I remember driving along at 60 mph, in 100 F degree temps, with the oil temperature gauge sitting at 210 F degrees.

 

Like Rusty, I had spent a lot to time making sure the engine compartment was totally sealed, and a section of the fiberglass under the grill had been cut way to clear the big 911 fan.  This allowed a lot more air to enter the engine compartment, compared to what I have now (stock hood/grill).

Everybody who knows says, "Setrab".

 

Henry generally puts 72 plate EMPI coolers in the wheelwell for those who ask for it, but I'm running the 96 plate EMPI. The 96 plate hangs out the bottom of the fender unless you modify it (I did).

 

IM's come without holes in the firewall. I added some- I wish I hadn't.

 

Your heads and exhaust will make a huge difference in general temps.

 

Ron is right about the case. I'm not sure why the AL bubble-tops run warmer but they do.

My Speedster is a VS and unless I'm totally whacked there are no holes in my firewall and I have a stock doghouse cooler.

I just ordered a Setrab and after it arrives I'll get it installed along with a remote oil filter. I'll see how much cooler mine runs.