Compression too high?

moxnix · Posted: Thu Sep 11, 2003 11:22 am Post subject: Compression too high?

Did a compression test on the 1776 in my bus after some heating problems; scored around 160 in all four- this strikes me as pretty high?

brackish · Posted: Thu Sep 11, 2003 1:29 pm Post subject:

Maybe that compression gauge isn't to be trusted.

moxnix · Posted: Thu Sep 11, 2003 2:27 pm Post subject:

as far as I know... this thing will hit 250 degrees + on the freeway.

pogolo · Posted: Thu Sep 11, 2003 2:41 pm Post subject:

Sounds a bit hot, but within the acceptable range I believe. How fast are you driving? How hot is it outisde? Perhaps if you slow down your oil temp will drop. 75mph will run you pretty hot.

moxnix · Posted: Thu Sep 11, 2003 3:06 pm Post subject:

Admittedly, we've had a warm summer up here- but I drive 55-60!
I've developed a nervous tick watching that damn oil temp gauge...

JamesT · Posted: Thu Sep 11, 2003 4:01 pm Post subject:

Well theres your problem. If you work on your own VW, never install a temp gauge. It'll make you paranoid. VWs are aircooled, so they do get a bit hotter the the water boys, but it shouldn't be anything to worry about.
Still, you should check to see if the cooling tin thermostat is hooked up properly, if it isn't, set it up right or remove it completely. Make sure you don't have any major holes in your engine tin (2 cm diameter or bigger) and maybe change your oil. Having any debris in you oil will cause friction and make it run hotter.
-James T

Amskeptic · Posted: Thu Sep 11, 2003 7:54 pm Post subject:

moxnix · Posted: Thu Sep 11, 2003 8:05 pm Post subject:

On the last trip we took the dipstick was searing hot every time I checked it- and this on a engine with less than 15 k and in perfect condition by any outward apperance... perfect timing-- everything in its place... And trust me- I sweat the details
I ended up covering the gauge up , and slowed down to 45 when the pos pinged.

NeverHadaBeetle · Posted: Thu Sep 11, 2003 8:39 pm Post subject:

Yes. A reading of 160 total compression is too high for a stock engine. When I say stock I mean stock cooling setup. You need to lower the compression ratio to decrease the total compression of 160 to 130-140. This will require removing the engine, removing the heads, and installing shims to enlarge the combustion chamber. You could also upgrade the cooling system with a larger external oil cooler or a deep sump. In the meantime I would run high octane fuel, use synthetic oil, and drive easier. I use the oil temp gauge only for a base line as it is not always a good indicator of engine temp. However, I don't subscribe to the ignorance is bliss reasoning for not using them as they certainly don't harm anything. In your case the oil temp gauge has done exactly what it is suppose to do and that is telling you 250+ degrees is too damn hot. Something needs to change. Good luck.
_________________
"Well, we shot the line and we went for broke
With a thousand screamin' trucks
An' eleven long-haired friends a' Jesus
In a chartreuse micra-bus."

JamesT · Posted: Thu Sep 11, 2003 10:08 pm Post subject:

But ignorance IS bliss. these engines can take a lot more than we give them credit for. The thing that will probably end up doing the most damage to your engine is trying to change your driving style to keep it cooler. When you drive to keep it cooler, it will most use more gas, like driving to save gas makes your engine hotter. I prefer to keep it in running order, but not care too much about my driving style making the engine too hot or whatever.
-James T

moxnix · Posted: Fri Sep 12, 2003 6:48 am Post subject:

thanks, NeverhadaBeetle- Thats the response I was fishing for... Out it comes. Again

moxnix · Posted: Fri Sep 12, 2003 7:50 am Post subject:

So... Can anyone tell me how to determine how thick the shims should be?

NeverHadaBeetle · Posted: Fri Sep 12, 2003 8:16 am Post subject:

Nobody can tell you the shim size until you pull the heads off and get all your measurements for cylinder head combustion chamber volume and deck height. This will determine your current compression ratio. This is something you can do yourself, but you need to purchase a kit to measure all this. The kit is basically a syringe with plastic disks that allow you to check the volume of the combustion chamber. Once you have this information you can determine the size of shims you need to lower the compression ratio to your desired setting. The kit is available at most VW suppliers. Don't be afraid to do the work yourself, but don't hesitate to contact a good shop for assistance either. If you remove the engine and heads and allow a shop to do the measurements and reinstall the heads then it shouldn't cost too much since it would probably take them less than 2 hours. You would then reinstall the engine and save yourself some money while letting a professional handle the more technical stuff. A safe compression ratio on a 1776 in a bus would probably be around 7.5:1 or less, but this is obviously something everybody has an opinion about. A lower ratio leads to lower total compression and a lower operating temp for the engine. Unfortunately you also lower the power output of the engine so you need to find a medium that you can be happy with. Good luck.
_________________
"Well, we shot the line and we went for broke
With a thousand screamin' trucks
An' eleven long-haired friends a' Jesus
In a chartreuse micra-bus."

moxnix · Posted: Fri Sep 12, 2003 9:07 am Post subject:

OK, thanks. Thats what I figured
_________________
Ritterlich im Kriege, wachsam für den Frieden

ratwell · Posted: Fri Sep 12, 2003 10:41 am Post subject:

Look for an inexpensive kit like this.
_________________
'78 Westfalia CDN
'76 Doublecab
Read the Baywindow FAQ


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