Remote oil coolers (followup)

Question 1: Where is the best (read; most reliable here) place to monitor engine temp? Some say cyl. head and some say eng. oil. Also, what is a safe temp range for these two methods?

Both: Read the oil temp read at the top of the oil gallery (where the normal VW temp sensor goes) and then get a 4-cylinder cylinder head temp set-up and place the sensors under each spark plug or, at the very least, #3 cylinder (usually the hottest, except when using a 911-type shroud and then the hottest are 2 & 4).  The two temps, while related, are quite different and change at much different rates.

Good rule-of-thumb figures:  

Oil Temp:  180F-220F

Cyl Head Temp:   275F-375F

Question 2: Has anyone ever installed an accurate magnahelic vacuum gauge (H2O) or H2O manometer in the engine compartment to measure if there is a negative pressure at maximum operating conditions? It seems that many owners are putting extra holes in the engine compartment, hood, etc because of perceived airflow restrictions.

Yes, it's been measured and there is (on a closed engine cover with no additional fan inlet hole in the firewall) a negative pressure going on when at speed.  That's why many of us have cut holes into the firewall in front of the fan inlet to provide more cooling air - the carbs seem to take care of themselves once the fan in satisfied.

On the Bergman "New and Improved" 911 fan shroud:  If it had been developed by Jake Raby and had his wealth of research and testing behind it I might consider one.  Probably still wouldn't buy one, but would at least consider it.  Why risk your engine, when you could install an OEM VW set of tin-work for 1971 or later (for much less $$) and forgetaboudit?

I agree that a 911 type fan shroud looks awesome.  I loved the way mine looked, but I would never buy another one.  There are better things to spend my money on...and I've found most of them    But, if you really what one, go for it.

Two gauges that are important in an air cooled engine, especially one that has been hopped-up, are a CHT gauge and oil temperature gauge.  The wire for a CHT gauge, which gives you the temperature of the heads, usually attaches under one of the spark plugs (usually #3).  The wire for the oil temperature gauge can be attached in a number of locations. Mine is attached to a sending unit just below my lower crank pulley

It is important to have both gauges because you can have high CHT temps, but normal oil temps, or normal CHT temps and high oil temps.  In my case I had normal CHT temps, but my oil temps were through the roof.

Here's the temperature numbers that I follow:

Oil

180-220 F  normal

220-240 F  warm

240+     F  HOT

CHT

325-375 F normal

375-400 F warm

400+     F HOT

To answer your questions-

1- head and oil temps tell you different things, so it is best to monitor both. Cylinder head temps are best monitored from under a spark plug (usually #3) for most real time response. Some heads have a boss for a f.I. temp sensor (which can be used), but all that really tells you is when the head (and engine) gets to operating temp. The gauge needs to be (temp?) compensated and the ones that are are not cheap. The VDO units are not accurate for this reason. 300-350' is not unusual for cruising head temps, with the occasional blast to 400. If your engine is always up around 375-400' then something is wrong.

Oil temps don't seem to vary all that much due to location; the oil moves so quickly through the engine (a stock engine will recirculate it's 2 1/2 or 3 quarts of oil 3-4 times a minute) that whether you install your temp sender at the stock oil pressure location or another place in the block makes little difference. If you can get your engine to normally run 190-200'F, that would pretty much be ideal. Short blasts that take it up to 220-230 (as long as you're not doing this all the time) won't kill it as long as the temp comes back down shortly after backing off.

2- A simple manometer to test engine compartment vacuum- anchor one end of a 15 ft. piece of aquarium airline tubing (1/8"?) to the fan shroud (by the coil is fine), have a helper sit in the passenger seat with the other end of the tube in a clear glass of water (easier to see what's going on) and see it there's a difference in the water level in the tube as the car is idling with the engine lid open and then closed. Watch what happens around town, and then during a cruise on the highway, again, with the engine lid closed and then open. A 15 or 20 minute drive on flat highway with it open and then back with it closed will tell you a lot, not only with the water level, but head and oil temps should confirm.

 Wildbill found a short piece of pool noodle worked well, and he discovered that while just putting around at the beach, oil temps came down noticeably with the engine lid open.

Some guys will add an extra cooler to deal with the high oil temps (the symptom) and not bother to figure out what's actually causing the problem (not enough airflow to the engine). Yes, the cooler will alleviate the hot oil temps, but if the heads are still too hot....it's going to eventually crap on you somewhere, and when it does, new heads aren't cheap, especially if they've had a bunch of porting work done to them, not to mention the towing back home and the inconvenience. The hole in the firewall is an easy way to ensure there's enough air getting to the engine compartment.