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Vapour Lock??
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sam_w
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PostPosted: Tue Aug 08, 2017 4:57 pm    Post subject: Vapour Lock?? Reply with quote

I have been driving my 'new' 74 white t
Thing quite a lot recently.
I went to Things West in Chino/LA and back(1000 miles), to see friends and relatives in Vancouver BC (2500 miles) and camping in Big Sur (400 miles)

It has gone well most of the time, but I now realise that a standard Thing without external oil coolers or temperature gauge, do not like going at 65 + in 100 degree heat. I have been stopped three times, and I thought it was a fuel blockage. I have installed a fuel filter I can see between the pump and the carburetor, and now I see that there is no gas, even with a full tank.

2 questions,
1) what is a safe speed in a standard 74 when the air temperature is over 100 degrees Fahrenheit?
2) What can be done to prevent/ameliorate vapor lock, beside just waiting?

BTW The 74 Thing is fine and I have just gotten 2 new rear axles, easier/cheaper than replacing the boots!
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mondshine
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PostPosted: Tue Aug 08, 2017 6:03 pm    Post subject: Re: Vapour Lock?? Reply with quote

Sam-
"By the book" maximum and cruising speed is 68.

Image may have been reduced in size. Click image to view fullscreen.


However...I would never risk that in 100* ambient.

Keep in mind that oil temperature is directly related to RPM.
High RPM = high oil temperature.

CHT is directly related to load.
High speed = high load (especially with the top down).

So you are fighting both factors at freeway speed, more so on a very hot day.
Without any instrumentation to tell you how hot the engine is, I would keep it under 100 (Km/Hr that is Confused ) 60-62 MPH would be a safe maximum with an intact cooling system on an engine in good condition.

Just my opinion; worth what you paid for it.
Good luck, Mondshine
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Wildthings
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PostPosted: Tue Aug 08, 2017 8:10 pm    Post subject: Re: Vapour Lock?? Reply with quote

Set your timing back a few more degrees in hot weather. 26 BTDC at 3500+ ( rpm hoses off) should cool the engine a bit. Running a thinner oil like 5w40 or 5w50 can drop the oil temp as well. You can insulate the fuel line if you are actually getting vapor lock. Make sure your thermostat flaps are fully in the open/hot position.

Verify that the fuel pump is sucking well, if one of the valves is not sealing well the pump will not suck well, adding some FI cleaner to the tank may help the pump work better. When you remove the inlet hose to the pump and block the nipple with your finger you should feel strong suction when you run the engine, minimal suction would indicate the pump needs help. Any air leaks on the suction side of the pump may show themselves more as the temperatures get up there.

Alcohol laced fuel will give worse problems as the temperature climbs as well. Running premium may help even if it is not ethanol free.

Your jets may be partially clogged from letting the engine sit for long with alcohol laced fuel in the tank. This will cause the engine to run hot. Removing the main jet and clearing it with a toothpick may be required.
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YDBD
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PostPosted: Tue Aug 08, 2017 8:50 pm    Post subject: Re: Vapour Lock?? Reply with quote

Another option would be to install an electric pump up front near the tank to force fuel to the engine compartment.

Or maybe your fuel pump diaphragm is weak/worn out...just a thought...
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sam_w
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PostPosted: Wed Aug 09, 2017 8:25 am    Post subject: Re: Vapour Lock?? Reply with quote

Thanks for the suggestions, I will try not to drive on the freeway when it is over 100, BTW Redding was 116!
I did find that it was OK when I drove at 55, so that will be my cruising speed in the heat.
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carsdlt
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PostPosted: Sat Aug 12, 2017 11:46 pm    Post subject: Re: Vapour Lock?? Reply with quote

Also try the "tennis ball trick" (look it up if you don't know) Cool
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Bruce
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PostPosted: Sun Aug 13, 2017 1:59 am    Post subject: Re: Vapour Lock?? Reply with quote

Wildthings wrote:
Set your timing back a few more degrees in hot weather. 26 BTDC at 3500+ ( rpm hoses off) should cool the engine a bit.

Retarded timing like that will make it run hotter. The only time retarding the timing helps is when your fuel's octane is too low for the engine. Presumably, the OP's engine is stock, and stock engines are fine on 87 octane.
Set the timing according to VW's specification.
Wildthings wrote:
Running a thinner oil like 5w40 or 5w50 can drop the oil temp as well.

5W-50 oil isn't "thin". Tar like that will cause the oil cooler to be bypassed. Causing high oil temps.

Start with an xW-30 oil, see how that works.
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Wildthings
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PostPosted: Sun Aug 13, 2017 3:11 am    Post subject: Re: Vapour Lock?? Reply with quote

Bruce wrote:
Wildthings wrote:
Set your timing back a few more degrees in hot weather. 26 BTDC at 3500+ ( rpm hoses off) should cool the engine a bit.

Retarded timing like that will make it run hotter. The only time retarding the timing helps is when your fuel's octane is too low for the engine. Presumably, the OP's engine is stock, and stock engines are fine on 87 octane.


Have you actually tried that to see? Didn't think so.

Quote:
Set the timing according to VW's specification.
Wildthings wrote:
Running a thinner oil like 5w40 or 5w50 can drop the oil temp as well.

5W-50 oil isn't "thin". Tar like that will cause the oil cooler to be bypassed. Causing high oil temps.

Start with an xW-30 oil, see how that works.


Again have you actually tried a 5w40 or 5w50 oil? When I tried a bunch of different oils weights a few years back I found the oil temperature was more dependent on the first number than the second.
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sam_w
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PostPosted: Sun Aug 13, 2017 10:31 am    Post subject: Re: Vapour Lock?? Reply with quote

multi-grade oils are easy to understand. the first number is the viscosity when cold, the second when hot. As you worry about oil temperature when hot, 5-30 is probably correct.
i used to use 20-50 in an old engine that had a flickering oil light when hot. lower viscosity will give more volume of oil, and we all know that Things are really oil cooled.
I think i will add a gauge.
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Last edited by sam_w on Sun Aug 13, 2017 11:31 am; edited 1 time in total
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Wildthings
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PostPosted: Sun Aug 13, 2017 11:29 am    Post subject: Re: Vapour Lock?? Reply with quote

sam_w wrote:
multi-grade oils are easy to understand. the fist number is the viscocity when cold, the second when hot.


Except that you will not see many people going to a 5w50 oil if they are experiencing low oil pressure because it will not bring the pressure up as much as 20w50 or 40wt will.

What I was taught 45 year ago by one of the lubrication engineers who worked for Exxon when they were developing their multigrades is that the oil pump will tend to see a 10w40 oil as a 10wt oil and the journal bearings will tend to see a 10w40 oil as a 40wt. When I did my testing I found no difference in the oil temperatures for any 5wxx oil, a 5w30 oil ran at the same temps as a 5w50 oil, which tends to support this theory.
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Bruce
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PostPosted: Tue Aug 15, 2017 11:15 pm    Post subject: Re: Vapour Lock?? Reply with quote

Wildthings wrote:
Bruce wrote:
Wildthings wrote:
Set your timing back a few more degrees in hot weather. 26 BTDC at 3500+ ( rpm hoses off) should cool the engine a bit.

Retarded timing like that will make it run hotter. The only time retarding the timing helps is when your fuel's octane is too low for the engine. Presumably, the OP's engine is stock, and stock engines are fine on 87 octane.


Have you actually tried that to see? Didn't think so.

I'm not dumb enough to do that. But I have seen the exact same effect when a friend had a defective distributor that wouldn't advance enough. His Lotus white car had a rear apron that turned brown in a few days.
Here's what happens when you overly retard the engine. The whole burn event happens later in the cycle. So much later that the burn is still happening when the exhaust valve opens, putting the burn into the exh port and exhaust. When you dump all that heat into the exhaust port, the head temps soar into the sky. This is what causes dropped valves. Do what you want with your own engine, but don't tell others how to wreck theirs. If retarding the timing that much had such a magical effect, it would be in the manual VW published.

Wildthings wrote:
Running a thinner oil like 5w40 or 5w50 can drop the oil temp as well.

Bruce wrote:
5W-50 oil isn't "thin". Tar like that will cause the oil cooler to be bypassed. Causing high oil temps.

Start with an xW-30 oil, see how that works.


Wildthings wrote:
Again have you actually tried a 5w40 or 5w50 oil? When I tried a bunch of different oils weights a few years back I found the oil temperature was more dependent on the first number than the second.

Yes, as a matter of fact I have.
I have made many road trips deep into Mexico and Central America, and am always looking for ways to reduce the need to do maintenance along the way. Like using a Pertronix so I don't have to dick around with points and a timing light. Before one trip, my buddy gives me some high end Euro synthetic oil and tells me I should be good for 10k miles on it. I didn't pay much attention to the viscosity, 0W-50 when I poured it in. Soon after I set out, I was stumped as to why the engine was running oil temps 20 hotter than normal. By the time I got to SoCal, I clued in. The -50 oil was causing higher oil pressure (as indicated on my gauge), and this caused the stock engine's oil cct to BYPASS the cooler. I dumped that high quality tar and put in my normal 5W-30 and saw the oil temps drop back down to normal.
Most likely, those lubrication engineers you talked to from Exxon didn't know anything about VW's oil cct and cooler, because almost no other car uses an oil cooler like ours.
As sam-w said, the first number is the viscosity when the oil is cold, the second is when it's hot. In order to earn a -50, a 5W-50 will be roughly the same viscosity as a 20W-50 when hot.
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Wildthings
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PostPosted: Wed Aug 16, 2017 3:27 am    Post subject: Re: Vapour Lock?? Reply with quote

Sorry, but for someone who pushes the use of 0w20 oil to come out and claim that they didn't check that the viscosity of the oil they were pouring in was 0w50 is a little much. Better come up with another story.

As for timing, Colin (Amskeptic), whose opinion I will take any day over yours runs 26 in his buses with either Type 1 or Type 4 engines and loves to show how low his engine temps are while crossing Death Valley on the hottest days of summer.
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YDBD
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PostPosted: Wed Aug 16, 2017 12:16 pm    Post subject: Re: Vapour Lock?? Reply with quote

soooo...vapour lock anyone?
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mondshine
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PostPosted: Wed Aug 16, 2017 5:56 pm    Post subject: Re: Vapour Lock?? Reply with quote

Sam-
re: "vapor lock"...
Is it possible that your fuel pump pushrod is temporarily seizing in the plastic fuel pump mount?


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