Engine hot on highway runs

[coonhunter]

I know that this topic has been covered many many times, but I wanted to create my own post to help keep me motivated and get much needed input on what I am doing.

The problem I have is that with runs down the highway above 65 mph for more than 30 minutes, I start to get a flicker from the save my bug dipstick. I can slow it down to below 60 and the temps will go back down and everything seems fine. I noticed this several times, but always attributed it to the 100+ outside temps, and just drove slow. Last night it was around 85 outside and humid, so I should have had no trouble. So here I am, looking for answers and documenting my progress.

To start, what I am driving:
-1968 Baja
-1835cc
-stock heads
-40idf webers
-engle 110 cam
-doghouse fan shroud, chrome, but it does have directional vanes and seams well enough made.
-dual cannon exhaust
-I do not know the compression ratio
-235/75-R15 rear tires
-VR1 30wt oil
-009 distributer @ 28deg total advance


So far, I have pulled the cooling tin off to check for any air blockage or poor fitment issues, and I found none. I am going to buy an IR thermometer so that I can get some actual data, which will help with the process. Right now I do not have any temperature gauges.

In a past post, it was suggested that I am turning my fan too slow at a given speed because of the large tires that I am running. At 60mph (per GPS) I am turning 3200rpm (per auto-meter tach), which according to other posts that I have read, that does not seem too out of the ordinary.

Things I am considering right now:
-Larger than stock crank pulley to compensate for large tires/low rpm at cruise OR using a 356 pulley to speed up the fan.
-Switching to a type IV oil cooler

Questions:
-What else should I look into to fix the problem?
-Does my speed/RPM ratio seem ok, or am I really spinning the motor too slow?

I should have some actual temperatures tomorrow evening as I will get a temp gun tonight and drive to work tomorrow.

Any help is appreciated, I have thick skin, so let me have it!

Thanks in advance.

[Brian]

Your tires shouldn't really be hurting you unless your r&p was a 3.8. Are you concerned that you're overheating just by the dipstick triggering the idiot light? Go on a long run and use your IR gun to measure the case, it won't give you an accurate reading of oil but will give you a good start. Measure at the galley plug under the distributor, the drain plug and the valve covers.

60@3200 seems fair and you should be getting good cooling to the heads which is your real concern.
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'68 Baja Truck
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[74 Thing]

What is your ring and pinion and fourth gear? You may not be turning enough rpm, it could be your jetting/tuning as well.

What size is your crank pulley? Most aftermarket are 6 1/2", but there are 7" pulley's out there as well. The easiest thing to do is put your pulley at TDC then put a piece of tape on the alternator pulley. Then turn the crank pulley one full revolution and count how many rotations the upper pulley makes. I am guessing it is somewhere around 1 1/2. By increasing the lower pulley to 7" and running a smaller pulley or a belt that runs lower in the alternator pulley you can get over two turns at the alt per one rotation at the crank. Make sure you fan is up to it!

Your shroud and crappy exhaust are not helping.

[mikedjames]

The Savemybug dipstick switch comes on at quite a low temperature.

I think it would be on solid on my bus in the same circumstances as I run at 65mph and 230F.

Your engine is larger than stock with stock cooling. It will run hotter than stock if it is producing more HP with the same efficiency.

Either buy a "proper" temperature gauge or throw away the savemybug .. it tells you the engine is properly warmed up sometimes...

And if it worries you fit an additional oil cooler.
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1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
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[rockurob]

Stock generator/alternator pulley 4 1/4" dia
356 Pulley 3 3/4" diameter
I just ordered and received the 356 Pulley halves and
hub from Pelican Porsche parts for
my 73 Thing
I also have 235/75/15 rear tires
using this calculator with my 4.125 R&P
am turning 2800 rpms at 65 MPH
http://johnmaherracing.com/calculators/gear-ratio-calculator/
I have not installed, but plan on before any
long trips..... for my Thing appears to run a little on the
warm side at highway speeds in 4th gear..... no problem
with city driving .... thus I have been avoiding
longer highway trips this summer
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61 Rag Project:
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[coonhunter]

I don't know my ring and pinion, or 4th gear ratio for that matter, I do know that 4th gear at 60mph = 3200rpm. According to the calculator, I should have some really low gears (numerically high).

I don't see the point in the tape on the pulleys, wouldn't it be easier to just measure the two pulleys and figure up the ratio between the two and then just figure up how much of an increase in fan rpm you would get by changing pulley size?

I will measure the temp tomorrow, I would have to kick myself if everything is the right temperature.

[74 Thing]

Different belt sizes and where the belt rides in the pulley determines the crank to alt pulley ratio so you need to measure your starting point and then the changes to see if you are increasing the fan speed or not.

[Brian]

yea, if you use a 356 you'll need a 900 belt. which is nla and 905 is the next size up
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Wash your hands

'69 Bug
'68 Baja Truck
'71 Bug
'68 Camper

Only losers litter

[rockurob]

[slalombuggy]

You are pushing a brick through the air. Bajas are big and dirty when it comes to aerodynamics so your engine is working more than it would in a regular Beetle, which generates more heat. I'd be concerned if it kept going up or stayed the same when you slowed down but since it drops, your cooling system is working OK. Fans will only push a certain amount of air and then they "stall" meaning they won't push any more. Speeding up the fan will only work to a certain degree and then you'll have to adjust your driving style.

brad

[coonhunter]

Good thinking slalombuggy. I am searching for a fastback, it should be a little more aerodynamic and work better at speed. For now I am content to drive a little slower IF I know that is really the best solution.

[MURZI]

What are your jets?? If your jetting is not dialed in, it will run hot. With my 1835 which was exactly like what you are running, in my baja, I used 52/130/200 28vents with 40 hpmx's. 13.0 afrs ....with a 010 distributor.
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2276
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[PumaVW79]

[74 Thing]

You can determine the ring and pinion by turning the input shaft (crankshaft) while in gear and the wheels rotation...from thesamba...

One way to determine the gear ratios is to put it in 2nd gear and count the number of input shaft turns needed to cause one turn of the axle. If the brakes drag, you have to compensate for that.

8 turns = 3.875:1
8½ turns = 4.125:1
9 turns = 4.375:1"
Marvin
PS if one wheel remains on ground then it's 4, 4-1/4 and 4-1/2 turns

[coonhunter]

Looks like I have some homework to do. Thanks for all the replies.

Working the numbers backwards, based on 60mph=3200rpm; I have a final drive ratio of 4.58. Assuming a fourth gear of 0.89, that would make my ring and pinion 4.12.

If I have the time, I will pull my jets tonight and look. I assume the 13.0 afrs is your air fuel ratio. I will not have the ability to measure that, but at least I can pull the jets and get your input from that.

If I ever have to pull the top end of my motor off, I will measure my compression ratio, but for now that is just one bit of information I do not have. I wish I did.

Thanks everyone for your help.[/u]

[Alstrup]

Your tach is a little off from the sound of it. Even if you have a 4,375 R/P. you should be doing about 104 kph (64-65 mph) So maybe you should check it against something else. The difference does not sound as a lot, but it is a huge difference for a relatively small engine.
A couple of things.
1. As noted earlier, you may be running a tad lean in the lower midrange.
2. The allways popping up venturi ring on the fan shroud does aid in better airsupply to the fan, thus helps with better cooling.
3. The addition/swop to a type 4 cooler in the stock fan shroud WILL NOT help you. That mod only helps if the engine spins faster than approx 3500 rpm. And even then it is minor due to the metered amount of air going through the cooler.
4. The tell tale dipstick may be a little off too. Check it against boiling water.
5. 100 degrees C. oil temps would not surprise me in a 100 F. ambient. and it is STILL not too much. Its getting close, but not alarming. I use to say no more than 105 C. on sustained high speed autobahn cruises in hot weather.
6. The addition of a larger lower pulley will aid in cooling the engine better all over. but you need to be carefull not to overrev the fan. 6000 engine rpm with the large pulley will equal about 6800 with a normal pulley.
7. With the IDF´s you may or may not have decent vacum out of the factory outlets. you shouldcheck before making the next step. But the addition of a SVDA distributor, or a CB Black box 9if you do not have any usable vacum signal from the carbs, can also help in reducing cylinder head temps so you get under the magic 100 C. on cruise, also in hot weather.
8. Of course an addition of an external cooler will help reduce oiol temps. but if you are actually overheating the cylinder heads the colder oil will not do that much of a difference apart from make you think that the engine is fine.

Soo, at the end of the day I guess you do have a little home work to do before you start making decissions.

Hope this helps.

T

[coonhunter]

Thanks Alstrup! I will find something to compare it with. I have been looking at the venture ring. It was quite cool today, maybe 78 during my drive home 75mph and my oil measured 180. I may not have as big of a problem as I think I do. I should know for sure soon.

[coonhunter]

Just checked my jets:
Idle 50
main 115
air correction 200
vents 28

I see my mains and idles are off from yours MURZI, should I consider changing them?

I am at about 3000' elevation if that changes things.

I have so much to learn! Part of the fun I guess.

[richparker]

Buy a IR temp gun from HD, they are only like $20. Then when your light flickers go back there and shoot it with the temp gun, with it running and get some real measurements. When I shoot my oil temp sensor with my gun it's always with in a few degrees of the gauge.

I'd try:
55 idles
120 mains
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[jberger]

What are your oil pressure and head temps? I would be more worried about those than oil temp.. Pressure drops with high temps and seats drop as well...