TheSamba.com :: View topic - Cylinder head temperature -- 1600 DP in 65 beetle

Tue Mar 20, 2018 7:58 pm

Cylinder Head Temperature (CHT)

Some time back, I put a CHT gauge in my 65 beetle. It had a 1600 Dual Port engine in it when I got it, and I always worried that with the bigger engine, the air inlet provisions may not be adequate. After I installed the gauge it always seemed to me that the CHT was pretty high at about 390 driving around town and over 400 at 60 mph, but I didn’t really have any idea what it was supposed to be, so on I went. I prop the deck lid (rear) open a bit in the summer, about enough that the bottom edge of the lid aligns with the bumper. When the weather cools off, I close the lid. Sometime around mid-November, I was in kind of a hurry to get across town, so I was running 65MPH+/- on the freeway and out of the corner of my eye, I caught the CHT gauge flashing, meaning it was over 450F. By slowing down to 55 I could keep it about 440F. I was complaining to a buddy about it one day, and he suggested we put the gauge in his 74 beetle, as it has a similar engine, at least theoretically, and his is original VW. I bought a spare sensor and hook-up wire. We put the sensor under number 3 spark plug (same as mine), and did a temporary gauge install in his car. Before we did the swap, as a baseline, I had run my car at 65 mph for some distance. I had the deck lid propped open as I felt the more nearly matched the air inlet area of his 74 as it has all the extra louvers in the deck lid. In this baseline test, my car ran a CHT of 390-410F (with 45-50F outside ambient), and we did the same with my friend’s 74. Low and behold, his CHT was 80-100F lower. I started messing around a little with timing and carb jetting. Got a few degrees improvement, but not much. I checked the gauge by immersing the sensors in cooking oil along with a known “pretty accurate” thermometer, and the gauge checked good. Within 5-8F of the thermometer from 200F to 450F. I decided to take the engine out and see what I could figure out. I thought perhaps I had the wrong fan (narrow instead of wide?). One thing I knew was wrong was the sheet metal that wrapped around the bottom of the cylinders. My engine had type 3 cylinder tin (marketed as “cool tin”) and I wanted to change that. Here is a paragraph from an August 1970 VW service bulletin discussing type 3 cylinder tin, with translation:

“Die neuen Leitbleche durfen nicht in Typ1 - oder typ 2 - Moteren eingebaut werden, da sie bei deisen Moteren die Kuhlwirkung verringern.”

“The new baffles should not be fitted in Type 1 or Type 2 engines, as they reduce the cooling effect of low - heat engines.”

I also wanted to check out the operation of the thermostat and the vanes inside the cooling fan housing that it controls. Checked the fan, it was the right part. I inspected the thermostat and vane system and found that it was not opening quite all the way, but very nearly. Didn’t think that would be it. I also took off the oil cooler. I didn’t think that would affect CHT that much, but still, it is part of the cooling system. There was a definite problem there. The engine builder had globbed some red RTV on the seals—way too much—which squished into the inlet and outlet when the cooler was installed and bolted down. I would guess flow area was reduced 80% or more. Oh—and it still had a small leak at the seal, as can be seen in the pic.

I knew that needed to be fixed, but I did not think that it was the cause of CHT over-temp. I wanted to change out the cool tin, which means remove pushrod tubes which means pull the heads, so off they came. The heads were aftermarket, and although I did not think that the heads themselves would be responsible for the CHT problem, but, since they were off, I decided to take the heads down to the local VW parts shop and compare to real VW heads, if he had any. Turns out he had two sets of NOS heads, one set from VW Brazil and one set from VW Mexico. When I looked at those, I thought maybe I had found the problem. There are air passages thru the head casting for cooling air to pass, and the open area thru the VW heads was multiples of the aftermarket heads. The first two pics are old head, the next two are of a new VW Brazil 040 head. I bought the new heads.

I put the engine back together with the new heads (which included new valves and springs), new oil cooler, new correct cylinder tin, plus the two rear air deflectors that had never been installed, plus various other parts like seals and gaskets. Buttoned it all up and hit the road, with the hood propped open (like the previous test). The outside ambient was about like the previous test (45-50F) but this time the head temp settled in around 300-315F at 65 mph—around 80-90F cooler, and close to my friend’s 74. I attribute this difference mainly to increased airflow thru the heads. One disclaimer: The sensor in all cases was under no. 3 sparkplug. I know that at that location the head temp is much lower, but I have no data on any other locations. My guess, based on the visual difference of the air flow area thru the heads, and the data, is that all (or at least most) of the cylinder head is running cooler now, but I can’t prove it. It is also possible that part of the change is due to replacing the type 3 under-cylinder tin with correct type 1 tin, and restoring full flow thru the oil cooler. I should also say that the car ran fine with the old heads. Had I not installed the CHT gauge, I would have been unaware, at least until a failure. However, I am much happier with 80-90F lower CHT.
These tests were done with the engine cover propped open, for reasons previously discussed. I also tested with the deck lid fully closed (similar speed and conditions). This adds 20-30F to the CHT. My long-range plan is to have louvers added to the engine cover so I can leave it closed in the summer.
A couple of other bits of info: I measured the combustion chamber volume on new and old heads—about the same. My calculations yield about 7.5-7.6 compression ratio. The engine is a stock-ish 1600 DP with a VW Brazil AS 41 case and was built with mostly aftermarket parts otherwise. I had previously replaced most of the tin with original VW parts, including the fan shroud and the movable vanes, thermostat (original Wahler) and all the linkage. When I got the car, it had the “36 HP”-shape dog-house shroud, no thermostat, no vanes, and all aftermarket tin. I did the thermostat and tin upgrade at the same time as I added the CHT gauge, so I do not have CHT data with the old fan shroud and tin, but I do know that cool weather warm-up and drivability was greatly improved with the new set up with the thermostat and shroud vanes.
One last thought—this is a description of my experience with my car. In no way is this intended to insult or disparage other people’s experiences or ideas. I share this only in order that it might help some other folks that are having similar issues.

Tue Mar 20, 2018 9:44 pm

That engine's builder was a hack.
Nice write-up & good to hear that the gage & sensor were tested.
Not having the same issue, but do recall that most of the OG heads I handled from the mid 70s-on had blocked air passages similar to the heads you pulled-off above.
Back then I did have some irritating overheating issues while using the same T3 "cool tins".

So, guessing that your old heads were chy-knees?

Wed Mar 21, 2018 4:38 am

I never had a CHT but had an oil temp on my old stock 74 bug, I use to prop the lid open like you said, It would always lower my oil temp on the highway at least 20 deg, and it had all the extra louvers in it!
Some people cut the lid behind the license plate for extra air flow.

Wed Mar 21, 2018 11:04 am

I don't really know where the heads came from--no "made in XXX"--but I do know they were not VW. Don't want to name names, but I have seen them around. From what I have seen, the engine builder was interested mostly in low cost, and was either not skilled or was in a hurry or both. I am not sure I would insist on VW heads in future builds, but I would want to look at whatever I plan to use before I write the check. Or I guess "swipe the card" nowadays.

Interesting to hear that the oil temp also drops when the deck lid is propped open, but it makes sense. I plan to add an oil temp gauge in the not-too-distant future.

Thanks for the comments.

Wed Mar 21, 2018 1:36 pm

Very good and detailed write-up, along with clear photos. Glad it has a happy ending.

Did you happen to measure your piston deck height when you had the heads off?

Wed Mar 21, 2018 4:16 pm

Plugged up heads run hotter folks. I have been saying this for years. It would be nice to know how much of the change was from T3 tins or the heads.

Dan

Wed Mar 21, 2018 5:46 pm

I did measure the deck height, with a depth micrometer. As one might expect, it was not exactly the same everywhere. About 1.5mm, some places a bit more, but I don't think it ever got to 2.0mm. Or in inches, .060 min, but not .08. I would say .060"-.070". Maybe .075".

I agree that it would have been nice to know how much was the T3 vs T1 tin, and how much was the heads. And even how much was the clogged oil cooler, but since I only wanted to take the engine out and back in once...

Wed Mar 21, 2018 6:20 pm

the oil cooler seals had 0 effect on the CHT.

Good work!

Wed Mar 21, 2018 9:39 pm

Agreed! I have experienced +400* F oil temp without the heads being too hot.

Good info and it all makes perfect sense!

Sat Nov 02, 2019 7:13 pm

I dont believe that is any conclusive results to say the heat was caused by the cool tin. It was the HEADS. I would like to see the engine with proper heads. . I have not ever found them to work worse than stock. My head temps are 240 to 260 with cool tin. On my 2007 engine with aluminum case. So no conclusive results to me. And that is in a bus.

The way if you look at cool tin they work with those heads would cause the engine to run even hotter. The cool tin meter the air around the cylinders and put more air to the heads by design. So if the heads veins were plugged off the air would have no place to go. I would try them without the veins plugged and I think you will be shocked to see that they do work.

Sat Nov 02, 2019 8:37 pm

my guess would be Autolinea GO1. Similar results were achieved in the HVW mag test with the same issue.

Ive found original 041 castings as well as GO3, GO4 with the solid chamber design will run hotter than the earlier thin chamber. If you notice on the 040 heads there is a slot cut in the fin right above the plug. This provides direct cooling to the plug itself that later castings seem to have left off. I got 50* cooler readings after modifying 041 heads with simple drillings between the fins.

Cool tin work fine when sleds are not able to be used.

Sun Jun 07, 2020 5:56 am

Hi
From reading your post, besides the sealant in the oil passage, there is one glaring problem with the engine before your rebuild.
The deflector tins are just that, they deflect the COOLING air around the bottom of the engine without these, of course the engine will run hot as the cooling air will pass straight down under the car and not cool the bottom of the barrels.
Who ever did the rebuild, either forgot, didn't care, didn't know.
Regardless of anything else you did if you had not replaced those cheap pieces of tin the car would have run hot.

The best way to keep aware of the cylinder temp is the installation of egt system, thermocouples are cheap as are a few op-amps and a micro-controller. Any electronics shop could build you one cheap enough.

Sun Jun 07, 2020 6:37 am

Strategically drilling the plugged up passages is cheaper than buying new heads. Be careful to not ruin a good set of heads. For the side fins I install two metal cutting blades in a $20 on sale HFT Sawzall, cleans up the flash quickly.

Dan

Wed Apr 26, 2023 9:18 am

MY guess is that the issue was the oil cooler plugged up then the head ports being restricted. I dont know if I would have made them that open. I think the small castings will help release the heat I would have made the holes a little smaller. Just a bit. Similar to the newer AA head design and the Panchito heads from CB.

IMO from experience We changed to cool tin on a performance engine back in the 80s. or early 90s. I dont remember which one it was But it might have been in the 1776 turbo and noticed head temp dropped a significant number. Just from changing the tin under the cylinders without any other changes. Removed the engine to freshen it up and put the cool tin under there (type 3). You need to think a bit....would VW admit their engineering was wrong.....Lawsuits would run up the flag pole.
If you look at the cool tin and evaluate them the metered hole for the cylinders. gives enough air for them to reach maximum cooling for a type 3. providing more air to the heads. This was for minimal air flow of the type 3 fan. When you open up the head ports you are allowing more air to move through the head giving it more ability to dissipate heat. the cool tin do the same principle. and form the air around the head. through more of the fins. The sheer principle of that has to work. More air flow removes more heat. But having those small castings also gives heat a place to transfer from. It is a balancing act. I would have not opened up the ports quite so much and left the cool tin on there. That is what I do now and have really cool running engines. no Detonation even when I floor it on a very hot day. sometimes over 100 degrees. with 8.25 to 1.

Wed Apr 26, 2023 9:22 am

Dan Ruddock wrote: Strategically drilling the plugged up passages is cheaper than buying new heads. Be careful to not ruin a good set of heads. For the side fins I install two metal cutting blades in a $20 on sale HFT Sawzall, cleans up the flash quickly.

Dan

I like how you left a little more of the casting on there. gives the heat a bit more surface area to release from. The other guys heads I think he did a bit much. Run those with type 3 tin and your golden. IMO...

Wed Apr 26, 2023 10:32 am

Type 3 tins belong on a type 3 engine with a type 3 cooling fan. They were designed to work together. VW said so and I personally have no reason to doubt their engineering.

If you do as most have done in the past and still do today, throw away 2/3 of the type 1 cooling system then perhaps the type 3 tins could partially make up for some of those missing parts... that to me would be the only thing that would make them viable to use on a type 1 engine.

Wed Apr 26, 2023 11:28 am

I think the redesign of the type 3 lower cooling tins had more to do with lack of sled tins underneath the engine. It just dumps straight out on a Type 3. The underside on other T1 based engines was much more shrouded to direct airflow.

I have no problem with T3 cooling tins on engines with the underside exposed to open air… like T3 engines, buggies, rails, etc. I think it is a good thing. But, I would not run T3 cooling tin on engines will fully shrouded undersides, like bugs and busses… it is redundant in those applications.

Wed Apr 26, 2023 11:55 am

A couple of comments: I did not modify the heads that were on the engine when I bought the car. Those were aftermarket heads. I bought NOS VW Brazil heads. I could also have bought VW Mexico heads, but I thought the Brazil heads looked a little better overall. But, the VW Mexico heads were also much more open for airflow than the aftermarket heads.
I changed the "Cool Tin" (Type 3 VW} back to the original OEM VW parts for type 1 engines, because the consensus on the forums seemed to be that the type 3 sheet metal was not as good for the type 1 engine, and, VW put out a service bulletin stating that type 3 sheet metal should not be used on type 1 engines. I quote that service bulletin in my original post from March of 2018:

“Die neuen Leitbleche durfen nicht in Typ1 - oder typ 2 - Moteren eingebaut werden, da sie bei deisen Moteren die Kuhlwirkung verringern.”

“The new baffles should not be fitted in Type 1 or Type 2 engines, as they reduce the cooling effect of low - heat engines.”

I recently got another translation:

"The new baffles must not be installed in type 1 or type 2 engines because they reduce the cooling effect on these engines."

Either way, VW seemed sure it was a bad idea.

It has been 5 years since I made these changes, and so far so good. Usually I have no difficulty keeping the CHT below 350, maybe a bit above under extreme conditions. (very hot day, high speed). Oil temp always below 220.

Wed Apr 26, 2023 2:04 pm

You have a winner!