Is it possible to have cool oil and hot heads? I run a 1776, 8.3:1 cr, std cooler, z9 in the guard, an extended sump and a secondary cooler above the trans. I posted a few months ago as the engine never seemed to get above 70 deg even when being driven hard for 2hrs on nite runs, I fixed that by insultaing the 2nd cooler, now in summer the insulation is off and the oil runs at 85deg in brissy on a warm day yet the engine still "smells hot" and the dipstick is hot to touch, the temp sender is taped into the back rite side of the case,
could the oil be running cool and the heads etc hot? Is it better to get a head temo guage? and what temp should this show? any help would be great!

It is possible to be overheating without audible pinging. For a start, the cylinders receive pretty much NO cooling from oil with the stock setup and the heads receive only supplementary cooling. The accepted practice for measuring head temperature is a thermocouple under the N03 exhaust stud, but as to the actual figure you should expect... If you could measure a healthy stock engine you'd have an idea, but, with an 8.3:1 CR you're probably running hot; depending a little on how hard you drive it. To run this high a CR you have to accept that your engine life will be shortened and you WILL need to have your heads checked well ahead of the stock reccomendation (100,000km.) Dropped exhaust valves are an age old problem in the VW engine.

its best to have both a head temp and oil temp gauge and only rely on them for relative values.

Head temps = Engine load - throttle to the floor up a steep hill in 4th gear will make head temps skyrocket.

Oil temp = RPM - Higher RPM equals more internal friction and more heat that is created and tranferred to the oil from bearings, piston rings, etc.

There is some overlap as there is oil cooling on the backside of the pistons from oil sprayed from the crankshaft as well as oil from the rockers reaching the valves.

Also remember that higher RPM will spin the cooling fan faster which will definitely affect head temps and oil temps (oil cooler in the shroud).

The place where u can mount the head temp sender (called a thermocouple) is underneath the sparkplug (usually no 3) as it is the closest to the combustion chamber, which is the bit that you should be most worried about.

Running a higher CR can actually reduce heat and increase power at the same time because you are increasing efficiency. You will also get better fuel economy & less carbon buildup.

however running 8.3:1 CR with a stock cam and stock ignition timing will probably make it run hotter and reduce overall engine life as 70 autostik said.

I have both Autometer oil & head temp guages. They work like a see saw with each other. On the expressway early in the mornings on my way to the track, I'm lucky to get oil over 70d & the head guage doesn't read at all. As soon as I get onto a huge hill, stick it into nuetral at about 120kph & coast down the hill, the oil temp will drop & the head guage will start to come up, get to the bottom of the hill, stick it back into gear & the head guage will drop straight back down again & the oil guage will come back up. Im now using a power pulley to get the temps up to acceptable levels. In traffic the head guage will rise & u can actually see it doing so, but as soon as u get going again & give it a few little blats to 4000rpm the head guage comes back down again. On the track it takes about 6 to 7 laps to get the oil to 100d & thats at around a consistant 4000rpm to 7000rpm. Head guage will rise as well but takes even longer. I'm running a wing as well as a type 4 doghouse oil cooler 7 also a Mazda Rx7 cooler above the gearbox with no ducting or fan. These low temps have only happened since I put the RX7 cooler on, before I could do 100kph on the F3 & the oil would easily hit 110d plus, now I can do 120kph & not see it go over 80d on a cool day & 90d on a hot day, huge difference.
Also I didn't use the head sender under the spark plug, I heard they are crap, I have the head tapped where the sheet metal screw goes & the oil temp sender is tapped into the case where a universal oil filler would normally go.
regards
Jak

I just took it for a serious run(brissy to northen nsw, 1.5 hrs) and the temp guage ran 80 at 100km/hr, 85 at 110km/hr and 90 at 120km/hr, thats with a 110cam and 009 dizzy, I also stretched its legs for a bit, and it got up to 97. I will have to get a head temp before next weekend when I do the run again.

[Edited on 31-12-2002 by BiX]

I think he means tapped Barry, drilled & tapped into the case.
Jak

sorry tapped, into the back of the case, about 25mm up and about 45mm from the right back side of the case. the sender is pointing foward into the sump. The other option is in the extended sump?

It sounds as though u have your sender exactly where I have mine, I can't think of a better place
Jak

Heh heh heh - NOW i understand. I just thought he mightnt be reading properly.....

Well now I have my engine up and going I am running head temp on num 3 and oil temp from a tapped sender in the rear of the block.

Head temp 350 - 400 F max so far. It really does move quickly when you put your foot down.
Oil 70 - 85 depending of what I am doing.

This is with 8.1 : 1 cr and a type 1 cooler in a dog house.