Overheating Problem - Found The Problem?

Was it overheating in town or on the highway? Single or dual carbs? What weight oil are you running? Engine size? Do you know the oil pump gear size? What cam is in the motor? Valve sizes? Porting? Exhaust tubing size? Is there a full flow oil filter? Extra cooler? Have you provided more air intake into the engine compartment than just the grille in the deck lid?

Could be as simple as you are running way too lean on gas/air mixture.

"had my mechanic check the compression ratio"

Just curious - to check compression ratio - you have to take engine out and remove heads to check volume capacity.  Not part of a normal winter tune up (a compression check is but not the compression ratio).  To go to that extreme did you know what temps were before adding the cylinder shims? Did you try adding extra oil capacity (extended sump) and/or an added external cooler?

 

ALB mentioned other needed details.  Plus aftermarket shroud? Proper size cooling fan for shroud (width)? 

The engine really heated up on a summer day on a long steep grade up into the mountains, but it overheated running on flat ground on a hot day as well.

 

I've been through a long list of things over several months and none checked out or helped.  This is the only item that seems to have some merit.

 

It's a 1915 from Vintage Speedsters (builder unknown) with dual 40's, mild cam, stock heater boxes, 10-30 oil, full flow oil with external cooler, don't know the valve sizes and porting, but probably stock, more air was provided to the engine compartment.  

 

Raby's pointed out that there is a difference between CHT and oil temps and that's why I installed the TC CHT and an oil temp gauge.  

 

I'm hopeful this decrease in compression ratio will help, the question is: how much might it help?  

Cole000what's the latest on your overheating---did you get it sorted out?

 

You were smart to not stop at an oil temp gauge and installing a Cylinter Head Temp gauge.  My CHT saved my engine two years ago while climbing the Tehachapi mountains East of Bakersfield after the Morrow Bay event 3 years ago.  The CHT gauge indicated a rapid rise in CHT and I immediately shut it down suspecting something was  in the fan.  Sure as hell that's what it was!  I had left some paper towel in the engine compartment---the oil temp didn't rise noticably although in time it would have risen but the CHT gave me an immediate reading and more than paid for itself many, many times over. 

 

Odd, the engine ran cool from Morro Bay and past Bakersfield so it was fine even with that paper towel in there but the climb up the mountains plus the paper towel was enough to get the engine hot.  I'll never be without a CHT in a Speedster!

I have a dipstick thermometer that I tested and was accurate.  The notoriously inaccurate temp gauge went further to the right than I had ever seen it, so that was what alerted me.  From then I checked it often and it was 230 plus all the time in the summer.  

 

I have the external cooler and we checked the thermostat, it was working correctly.

 

After my mechanic and I checked everything we could think of (including running it with the engine lid open to give it maximum air) we suspected it could be compression ratio, a cheap way to get more HP at the expense of running hot.  

 

So now I wait for summer to see if it's fixed.

I had a similar problem with my 2276.  I thought my dash oil temperature gauge was accurate, until I checked it with an oil dip stick gauge and temperature gun.  When  my dash oil temperature showed 180 the dip stick gauge showed 210.  On a couple of occasions my gauge hit 240.  I can only imagine what the real oil temperature was.   My engine is now out and apart for inspection.  Interestingly enough, my heads never got anywhere near being hot.

 

Cole- What weight oil are you putting in that thing?

10-30

I have a wire grill cover over the fan intake on all my Vws to help keep leaves trash and even mice out of it.   A mouse can make a whirling noise and knock out a gen/alt bearing   A paper towel could realy do your rings in and make a engine that will not crank hot because of low compressin caused by piston ring tencion falure. They can be replaced and it lives on. hope thats not the case on your problem

Wolfgang asked a question that you didn't answer.   (look for his posting above)   To check compression, the engine must be removed, the deck height measured and the heads cc'd.   Did you mechanic do this?    Did he add shims to reduce the compression?  

Sorry, yes, my mechanic pulled the engine, removed the heads and measured everything.  Compression was 9:1 and he reduced it to 8:1, which he estimated lost about 8 HP.  

 

I found a chart on the Internet that showed if you go from 8:1 to 9:1 you would gain 3% HP and so Im assuming that's about what I lost.  I don't know how many HP I have in a 1915, but assumed no more than 100?

 

We also installed a temperature compensated CHT and an oil temp gauge, so when summer rolls around again I'll have a better idea of what's going on.

I'm surprised because VS 1915's just have bigger pistons and cylinders; the rest (heads and cam) are stock. Try a heavier oil too; at least 30W; I use Shell Rotella 30W. And yes, lowering the compression ratio will definitely help in lowering your temps as well as allowing you to use lower octane gasoline.

A 30w will run cooler than a 10-30w?

Once it reaches operating temp I think it will perform the same; but until then the 10w-30 will lubricate better.

My bad, I meant 40 W. Since my car is in the tropics (no real winters here) I went with the VW Manual recommendation for tropical climates. Some mechanics even recommend 50 W, such as Harley Davidson oil.

Remember that when VW originally wrote those recommendations, multi-grade oil was more expensive and being an economy car, they were for the cheapest route to do the job (protect the motor), which a single grade does adequately. With a single grade oil there is a period right after start up where the bearings aren't being lubricated as well as they could be; a multi-grade (especially a 10-xx or even better a 5-xx) is thinner at start up and flows through the bearings to protect parts sooner than a single weight (especially a 40 or 50w) will. With a single weight oil you'll get fantastic pressure (especially before the motor warms up), but for proper heat transfer and protection the motor needs the oil to flow through the bearings, lifter bores and everywhere else. This doesn't happen when a motor is cold and it has 40 or 50w (and to a lesser degree, 30w) in it. When not up to operating temperature, single weight oils are like tar, far too thick to protect the motor properly until the motor is warmed up. I worked at a friend's VW shop for a short time (4 months?) in 1980 and everything just looked a little more tired at rebuild time in motors that were run on heavier single weight oils. I'm guessing that if we'd charted mileage, motors fed a steady diet of multi-grade would have generally lasted a little longer. But that's only a guess....  

 

My other point is that VW aircooled motors are pressure dependant for oil cooling (there is no thermostat for the oil cooler) and in some motors a heavier than needed oil (single or multi-weight) can bypass the cooler until it gets hotter than it should. The passageway to the cooler closes when pressure rises above  about 45psi. This is to ensure faster warm ups, and heavier than needed oil will disrupt this function. It's generally accepted that oil pressure (when a motor is warmed up) is in the proper range when it's approximately 1/100th the rpm (8-10 lbs at idle, 20 lbs at 2000rpm, 30 lbs at 3000rpm...) and oil that is too heavy  will create too much pressure when warm, bypassing the cooler and causing the motor to overheat. If extended highway running creates higher than acceptable oil temps and you're using a heavier weight oil something needs to change. If your oil temp gauge is accurate and oil temp regularly gets above 225' F, it's too hot. An extra cooler (with thermostat for shorter warm ups) would work, by why go to the trouble and expense when the solution is so obvious? And yes, I know that some bigger motors need extra oil cooling, but that should be done only after everything else is addressed.

 

Re VW's recommendations for different ambient temperatures; listen to what the motor's telling you. You may find that it's happier with a thinner multi-grade than you think. I think the perfect oil would be a 0w-30 zddp (zinc and phosphorus) rich, hydro-cracked (or even full synthetic); too bad the market's not big enough for anyone to consider it.

 

This all assumes that the motor has the proper oil pump (for most motors 30mm gears are too big! too much hot pressure, remember?), there is adequate air intake into the engine compartment (will cause overheating at highway speeds) and the engine compartment is properly sealed off from exhaust heat and spent cooling air.

 

Sorry for the long winded piece; I had a lot to say....Al

Don't apologize for the length of your post,   Well Said!!!!  (or in this case, written)

That is a very illuminating post; wonder if 10W- 40 would be a good alternative, then. Thanks for sharing your knowledge!

You could try it, noting your pressure at various rpms when the motor warms up...

 

PS- an easy way to tell if the motor's too hot; spit on the case. If it sizzles, it's too hot...

We all have our opinions on oil.........there have been COUNTLESS threads on this...

 I recently tried a little switch from 50wt. to 40wt.,all I got was lower idle & cruise oil pressure and 5 degrees higher engine temps (per Manly dipstick). I went back to 50wt.,and will stick with that. I do have performance motor with no thermostat and it is in Hawaii,so it is tropical. If I lived in a colder climate,I may consider a multi grade,however VW engine do run hot and the oil WILL thin out,the thicker oil will resist the viscosity change with heat more than a thin oil.  The VW engine is small,there is TONS of splash lubrication inside the engine,since the cam is actually under the crank and the heads do not need oil pumped up into them like every other car,so the need for "cold flow" is over rated for this motor IMO. Just let her warm up for a few minutes before rippin' it to 6K rpms!