Overheated but temp OK?

[magicmike]

91 Vanagon stock engine. I just broke down on a long hill near yosemite. (Near Mi Wuk Village) 96 degrees outside. Couldn’t hold 4th , then couldn’t hold third, then dropped to second, sputtered and stalled. Waited 20 min then it started again but similar story. Temp needle is just above the light but no warnings. Heard a bit og subtle gurgling in the engine bay but no leaks. Could it overheat without the temp guage showing its overheated? Any ideas? Appreciate any help. Thanks!

[Ahwahnee]

I'd (visually) check the coolant level in the tanks, especially seeing if the pressure tank is still full. The left one:

[DanHoug]

[Wildthings]

Dribbling some water on the engine block or heads will give you an idea of how hot the engine is. If the water balls up and dance around like crazy that would show that the block is above the boiling point for whatever altitude you are at.

An IR guns is a very helpful tool to have around as well.

[Wildthings]

Did your fan kick on? Hard to heard the lower speeds over the other sounds of the vehicle, but when the fan kicks on high it sounds like a prop plane taking off. When you turn the heater on and it dump tons of heat into the cab, that is a pretty good indication that the engine has enough coolant for the radiator to be able to do its job. The heater(s) can be used to bring down the temp if need be if the fan isn't kicking on or the cooling system isn't up to its job, though at summer temps the heater(s) will roast you pretty quick.

[magicmike]

Thanks everyone for the responses and knowledge.

So I checked the coolant level and it was fine. The temp light seems to work fine when you turn the key. I let it rest for 40 minutes then it started up and drove ok. I started thinking it’s an altitude thing. The issue started at about 4000 ft elevation (my van is normally at sea level). Anyway, I kept driving - It’s a big hill up Sonora Pass and it didn’t have much power in the 3500RPM to 4000RPM range. It liked being around 2100RPM to 3000RPM. I climbed like this to about 7000 ft elevation, then in a really steep section, I had to go all thecway down to first gear and then the issue happened again- sputtered and couldn’t even make it in first. I pulled over, let it rest, then looked in the repair manual and noticed an altitude adjustment (CO?)in the fuel system. It was an allen head- I tried turning it clockwise 1/4 turn. Started it up and it drove ok once again. I made it up and over Sonora Pass (9000 ft elevation). Then got down to 395 which is more flat. Driving to Mammoth on 395 it still felt unusually underpowered on the flats and especially on gradual climbs. I messed with the adjustment screw taking it back to it’s original setting and also counterclockwise a 1/4 turn. I can’t really tell if it is making a difference or not. I’m kind of stumped. Any ideas? Is this typical Vanagon behavior in hot weather + high altitude + steep grades? Any other things to check?

[djkeev]

I'd check compression.

You might have burned a valve or piston edge.

Look at the plugs, are they healthy?

Your wires could be jumping spark before the plug?

Moisture in your distributor cap?

Cap & Rotor burned or center carbon shot?

Clogged air filter?

Catalytic convertor clogged or it came apart and clogged the muffler?

Just spitballing here on hot stressed potential engine problems

Dave
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[Igeo]

That's tough terrain you are on. Sonora is the steepest grade in the Sierras- up to 26%. Then 395 to Mammoth and Bishop has several grades, and your elevation is all high enough to sap power. If you are used to sea level power, then the loss of HP at elevation can be disconcerting. The adjustment on your throttle body will have no effect on power by the way. You might want to replace the fuel filter though. If it's restricted, that could create the issue you are having. Sit in the hot spring down off Benton Crossing Road and relax.
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[sbw]

Summary: Your '91 will already have a fuel tank with a larger outlet and probably a different arrangement of filter(s) and pump than my '84, so the work I had done after a similar problem may not apply. But you might check carefully whether your fuel tank outlet is partly blocked by debris, or the fuel lines or filters are not clear, or the fuel pressure regulator is tired.

At high altitude, high outside air temperature, and high power, you're pumping a lot of fuel with a hot pump, back to a hot engine compartment, and then back into the fuel tank. That increases the temperature of the fuel in the tank. Then as the pump sucks the hot fuel back out of the tank, the suction might cause the fuel to vaporize before reaching the pump. And the pump can't pump vapor. All of that is my not-at-all-expert opinion, based on a very similar experience I had:

I was traveling east to west along I-80 through the mountain states in summer, 2018, in my '84 Westy with a GoWesty waterboxer and manual transmission. It was very hot, over 100F sometimes, and very high, up to 9K feet. The engine temperature and coolant level were fine, so I drove up long grades as usual, with the pedal to the floor and down shifting as needed.

During long climbs, the engine would miss slightly, then worse, then it would lose power and stall. After a rest, it would start up again, but the problem would return after a time.

Along the way, I replaced spark plugs and wires, fuel pump and filter, and more I can't remember. The problem persisted. In the end, I finished the trip through western Nevada and over the Sierra Nevada at the Interstate's minimum speed limit. A light touch on the gas pedal seemed to be the key to keeping the engine running smoothly. I had forgotten that I-80 from Reno to Donner Pass isn't very steep, so that went OK.

I took the van to Peninsula Automotive in Campbell, California. They couldn't reproduce the problem in cool weather near sea level, but they said they could hear the fuel pump cavitating in some circumstances. They recommended replacing the fuel tank with a later model with a 12mm outlet (like the one in your '91). I grudgingly agreed, even though it felt like a big expense given we weren't certain that was the cause. That also eliminated a change in diameter of the fuel line around the fuel filter and fuel pump, can't remember the details on that. They also replaced the fuel pressure regulator because it wasn't holding pressure after switching off the engine (and pump).

I haven't had to drive in >100F above 9K feet since. But the fuel pump is noticeably quieter ever since. And the problem hasn't returned, even on several climbs over the Grapevine in both directions. That's not as high, and it wasn't as hot.

I think it's worth your time to ensure the fuel can flow freely from the fuel tank to the pump in extreme conditions, if you can.

[Matt Wilson]

For a watercooled vehicle, you can use some quick thinking and crank the heater full blast if you fear you are overheating, just roll down the windows and suffer. It may let you limp it and cool it down quick without breaking something.
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[magicmike]

Thanks everyone for the thoughtful responses and ideas. Just got back to civilization.

Update: After backpacking in the Sierras, van started right up and ran fine though a bit underpowered as I drove through Mammoth area. Then I drove south on 395 to Los Angeles and it ran totally normal. Outside temp was about 80 degrees). No more lack of power. Engine temp consistently below the warning light.

The symptoms it had while going over Sonora Pass with hot weather, high altitude and a steep grade sounded exactly like what SBW described during his drive in high heat and high altitude.

Hard to believe my van can go from stuck on the side of the road to running fine just with a little rest and a change of altitude. But I’m glad it got me where I needed to go. Thanks again everyone!

[Wildthings]

You may have had a tank venting problem. Vacuum is the lack of pressure and pressure is what is needed to push the fuel from the tank to the fuel pump, so if your tank has a vacuum because the ventilation system isn't doing its job you might not have enough pressure in the tank to force the fuel to the pump, this would be exasperated by heat and elevation. We should of had you loosen the cap when the problem occurred to see if that cleared the symptoms up.

[oceanair]

Let's talk about air density and altitude, two factors.

Hot air is far less dense than hot air. Imagine a box of air and how many molecules of oxygen there are in it when it's cold and how many fewer there are when it's hot. Then the same principal happens when you move from sea level to 9000 feet, far few molecules per given volume.

These two factors are compounded especially at 100 degrees. I am guessing that our underpowered vans with such a high density altitude was the issue.

Using a density altitude calculator, 80 degrees at 0 feet is the same as 1300 feet. of altitude. 95 degrees at 9000 feet is the same air density as 13550 feet. Imagine walking up hill at 13500 feet... low power

Need oxygen to burn and there was little of it.

https://wahiduddin.net/calc/calc_da.htm
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[danfromsyr]

Generally speaking, an engine loses three percent of its rated power for every 1,000 feet of altitude gained. This means you could lose as much as 20% of your vehicle’s horsepower if you drive it from sea level to Big Bear Lake (with its 6,750 elevation)
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[sbw]

@oceanair, do you mean to say we should expect our Vanagons to stumble and die above a particular density altitude? I agree we should expect lower power at high density altitude, but it never occurred to me the engine might just fail.

Anyway, the engine starts back up and runs OK after a rest, even at the same density altitude. That suggests the failure might have a different cause, like a poor flow of fuel from the tank to the pump, as I believe my van had.

In my earlier experience with my van, it ran great at high altitude. It even got higher mpg.

That mirrors my experience as a pilot: I've done a lot of flying in underpowered aircraft with carbureted piston engines, sometimes at density altitudes above their service ceilings. It can be a challenge to climb to those altitudes, as the engine loses power as the air gets less dense. But once at altitude, the plane turns in higher speeds, even at much lower horsepower, because the less dense air produces less drag.

I believe a Vanagon can run well at very high density altitude, if the fuel can flow smoothly from the fuel tank to the fuel pump. I know I'll have to down shift and go slowly up some grades with the pedal on the floor, but I don't expect the van to sputter and die. I may be wrong, but until now I haven't heard anyone suggest that effect at high altitude.

[Wildthings]

If his problem was caused just by altitude and heat then every Vanagon owner who drives in the same conditions would experience this and there would be Vanagons parked along the sides the road cooling off near every high pass.

[oceanair]

Sputter and die -- no... it should not.

If you're not perfectly tuned, with no vacuum leaks, strong ignition, plugs, wires and coil... it will all affect running under those ow oxygen conditions...

Be sure ignition and vacuum lines are perfect, as well tuned as possible. Clean fuel filter too...
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[smirby]

I can add a corroboration/additional example from just a couple of days ago. The problem as described above fits perfectly my situation: high altitude (and climbing) on a super hot day but the engine not even close to overheating.

Symptom: Loss of power in a way that was NOT ignition related (tach didn't bounce down to zero), no "stumble" or rough running indicating a bad spark plug or even an injector.

Diagnosis/solution: let it cool on the side of the road (oh my god it was hot out there), for at least 15 minutes. Eventually removed cover from fuel pump area (Canadian van with gas heater, so there is a large protective cover that blocks your view of the fuel pump). With this cover off (and the much longer wait while that was done), the van started and ran fine for the remainder of the trip home - including an even higher (slightly) mountain pass climb.

I agree that this should NOT happen, and suspect that my fuel pump may be marginal in these kinds of extreme conditions as it is now almost 35 years old (tank and fuel filter are five years old).

Wish I had read this before it happened, as at the time I had only the vaguest idea of what was going on. These accounts definitely reflect exactly my experience and (eventually) the van ran fine and I was able to complete my trip.

By the way, the last couple of hours of the trip were in even hotter (by 5 degrees - all the way up to 43C) conditions but at sea level. The van ran perfectly. And the cooling system kept it running fine despite an hour long tailback behind a traffic accident, so air flow was particularly bad. I was super impressed with the ability to NOT overheat. I did run the rear heater - an argument for keeping it - and that helped keep the engine temperatures down. It made life in the van a living hell (49C) for a while, though...

...r

[smirby]

[magicmike]

Interesting discussion- Drove the van home from L.A. to San Francisco andvran perfectly. After reading everyone’s ideas, I feel like SBW’s description of the problem being fuel system related might be what my van was experiencing.

I do think I have some sort of fuel tank venting issue with my van- even in normal everyday use at sea level, when I come to a stop at a red light, after a few seconds, I hear a clunk soundcwhich I believe is the fuel tank sort of popping/ expanding after having a lot of suction- hard to explain but I’ve heard of this on another thread and never found a solution. It has a louder clunk if I have less fuel in the tank. Perhaps this suction issue doesn’t affect normal driving but at high heat, steep hill and high altitude, it may be the cause of the sputtering and dying my engine was doing over Sonora Pass. Anyone heard of this issue?