Perhaps Boyle's Law gives a hint . . . the relationship between pressure and temperature . . . and we need to take care when talking of "dry" or "wet" air as influenced by ambient temperature.

There are few places here in Oz, where alpine winter temps vie with your annual winter survival . . . but for some years back in the early 70s, I was supplying clinical services for a bunch of hospitals up in our Blue Mountains. Bought a brand new Japanese car, which proceeded to make my life hell. It was a great sporty vehicle but, pushed hard in very cold weather, it would suddenly choke itself to death after about 20 minutes of hard driving. Standing with engine off for 5 minutes, car would re-start with no problem until 20 minutes later, it would die once again. Dealership checked and re-checked, but in the relative warmth of their workshop, could not replicate the problem, nor explain it.

Eventually solved by a regular delivery driver on the road, who pulled over as I coasted to a halt, pulled off the air cleaner and pointed to a veritable donut of ice, perhaps as thick as a large, thick coin . . . and which extended out from the central choke tube of the carburetor almost to the outer rim . . . a strangling by accumulation of solid ice.

First, the cause . . . then, a range of solutions. First, ALL air contains a proportion of water vapour, largely fixed in relative volume despite notions of "dry" air but influenced by variances of temperature and pressure. If Boyle's Law is perhaps better remembered for massive temperature increase when an enclosed gas is subjected to great pressure . . . the corollary is equally true . . . the greater the vacuum enforced at the carby by continuous full throttle in sub-zero conditions, then a corresponding and huge drop in local temperature results . . . and the water vapour freezes out as described.

The solutions ranged from (a) backing off and driving more sedately (never!) . . . or (b) waiting at the roadside while engine heat soak quickly thawed out the iced carby . . . or (c) remove air cleaner, unzip and aim warm liquid at offending ice! Turned out there was a further option . . . (d) sold car; bought Mk1 Jag, much modded with triple SU carbs; and never again had same problem.

The example of what specific areas of an aeroplane need de-icing and why seems appropriate . . . again, Boyle would be delighted for, no matter how cold the air outside, good old suction . . . the negative pressure over the aerofoil wing that produces uplift . . . can be guaranteed to lower the surface temperature even further. I understand that if the ambient air temperature is -30C at a given altitude, this suction effect can produce a localized wing surface temp of -60C just aft of the leading edge (seeking further independent verification).

If, as Mikey says, this SC is doing little hard work in compressing the air and its inherent water vapour during a careful, significantly sub-zero drive, then not only the intercooler but I suggest, induction vacuum may be freezing out that water vapour as solid ice . . . which later melts under heat soak, then run where it may, only to re-freeze in a place where it could cause grief. Bizarre . . .? Sure, but it fits both the science and my experience. Proof seems to lie in what OP found.

However, it's a big snag that [JagV8] points to. Why only the SC and not its NA siblings? I fear I have only added part of the answer . . .

Cheers,

Ken

 

Hi Ken-

What you experienced was carb icing. This is a very well understood and common occurrence on older carb equipped cars. I'm no stranger to it as would anyone who grew up with such cars and (as always) thought they knew better than the designing engineers and threw away all the stupid hardware under the hood that didn't contribute directly to going fast.

In addition to an early '70s V8 powered car that I erroneously meddled with, I found that my Norton Commando 750 carbs would stick open unless the engine had been well warmed prior to setting off. Very exciting.

Any modern day aviator flying a piston powered aircraft is well versed in 'carb heat' for the same reasons. EFI engines have a heated throat at the throttle body valve to prevent such icing. I've read about owners disabling the heat thinking that it will contribute to performance and am waiting to read about one who moans about 'a stuck gas pedal' as a result.

NA engines don't suffer the hydrolocking issue as there is no supercharger that might (under the perfectly wrong conditions) heat the air just enough to melt any airborne moisture as it passes through nor do they have intercoolers in which said water vapour might accumulate (and under the same perfectly wrong conditions) freeze because they are being actively cooled. If I were a type R owner and lived in an area were hydrolocking was possible, I'd find a way to keep the intercoolers above freezing conditions. Blocking airflow?

 

Yep, agreed. Perhaps a case for temp sensor controlling a rad blind or intercooler heating wrapper?

Or, as suggested earlier . . . finish each such drive with a short period of idle down to allow engine heat soak to melt any ice formation and ensure such is ingested and exhausted before shutdown? Good project for a timer?

Cheers mate,

Ken

 

I ran a 2001 Millenia S for 12 years including annual pilgrimages to Alberta in winter in temperatures down to -37C. Never experienced any freeze up. This engine had air cooled charge coolers.

 

JagV8: I own 2 03 STRs. They are identical and bone-stock in every way. Neither of them have had any real issues. An occasional coil failure in both and the under-the-supercharger-hose failure in the blue car.

The white STR froze on Thursday after an hour and a half long drive at -20 C. I accepted this as built up condensation that could only occur during a long drive. However... needing a way to heat up the white car, I drove my blue STR to a friends house to borrow a "salamander" diesel space heater. It was a 20 minute drive on super icy roads on a frigid night, again close to -20 C. When I got there, I just shut the engine off, not having learned any lesson. About 3 hours later when I left, I stuck the key in the ignition and it cranked for about 2 seconds and stopped solid, exactly as the white car had done before. I am willing to bet anything I have the same ice build up.

So I now have the first two cases of the year, both within a few days of each other and both still waiting for me to defrost them today. I am thinking that I will get a little more scientific today and investigate the source of the water in the blue car and see if I cant find traces anywhere.

 

How about a switch to turn off the SC Pump?

Although this might cause an error code.

 

As they say in Newfoundland, 'whale oil beef hooked!'

There's a new one. Look forward to seeing what you find in the blue car.

 

Another one? At the same (rough) location? I second Mikeys response!

About turning off the intecooler pump, it may set a code if the conditions are right. i had mine fail on our STR a few years ago. Threw a code and RP. I cleared it to make sure that was the actual problem (if it came back) but it also was just heading into our winter deep freeze. The code never came back until it started to warm up again. I think it measures some type of temperature difference between IAT 1 and 2 (or something like that). Due to extreme cold temps, the difference between the two never tripped the code. I guess that supports the idea of intercoolers being below freezing under the right conditions.

Now, I have experienced a frozen starter a while ago on the STR. They had plowed our parking lot here and left the wonderful 2 foot wall of snow behind the cars. The wife left for work and backed over it. She must have picked up tonnes of snow and packed it in everywhere. When she got to work she also had to drive over a pile of snow to park. Car wouldn't start for her when she went to left. Was actually -42C that day. BUT, unlike the issues above, the car didn't try to start and then suddenly stop. You could hear the starter try to do something, but then it actually got frozen/stuck ON. Instantly drained the battery. I had to pull the relay to turn it off. Just had to get it towed home into the heated garage and let it thaw out. Had to get a new battery, but started/ran perfect after that. Now, not the same thing as here, but ya, ice can be a pain.

 

I could believe two cars in a couple of days because both
cars were in the same geographical region and subject to
the same weather.

The thing about the S-Type and X350 is that they are both
front breathers whereas the X308 grabs its air from the RHS
wheel well.

What about the effects of EGR and the breathers? Both of
them bring warmish, perhaps moist air or at least gases.

What if the coolant preheat circuit at the TB was not working,
or the auxilary pump that circulates the coolant in that circuit
is on the fritz, or the egr valve is on the fritz? Then the warming
effect of those two would not be present.

 

Yes! EGR and PCV will bring exhaust gas which of course includes H2O.

SC pump disabled will indeed likely bring a code and RP (and yes it knows via IAT2 not reporting as expected).

Sorry to hear another STR was affected - but kinda helps (hopefully!) with figuring this.

I didn't know about the 4.0 SC (not used in the S-Type) having a different air intake. Useful to know.

Now... why hasn't WinterJag suffered? (Er, not wanting it to occur!) Why haven't more 4.2 SC front air intake cars suffered?

I'm finding Mikey's explanation much more plausible... but... why not when the cars were younger?

 

Is the EGR different on a 4.0 SC car? On a 4.2 the EGR, if working properly, is allowing quite hot gases to pass into the elbow below the TB.
It is way too hot to touch on a warmed up engine.

 

So the official verdict: cylinders 5 and 6 were completely packed with ice. I dont know an exact volume, but I would estimate a few hand fulls. 5 and 6 are sequential in the firing order so it makes sense that both would be on intake stroke at the same time, thus allowing water to fill the cylinder. I spent a very long night with a space heater warming the engine back up to temp and using the starter to shoot out the liquid water. It cranks freely with no weird noises so I hope it runs well. I have yet to get to the blue car, as the white car turned out to be a much larger fight than I thought.

 

On 2nd thoughts I think EGR is irrelevant.

Still interested in answers to post #20.

Also, in what mode was the climate control? Auto or what?

 

After reading all this now I'm getting nervous every time we start one of our cars! Again, based on all the theories here, I should have already had this issue over the years and combined kms over winter. Don't worry JagV8, You all will be the first to know if I ever do suffer from this!

 

Someone in another thread mentioned having removed the (top) engine cover - which I suppose would not help in cold weather.

So that's another thing to mention if a frozen engine has it removed.

 

Hi guys, I just wanted to pop in and share my experience with this problem. The last two days last week were very cold, around 0F (-20C) both days. Thursday was fine for my XJR, as was driving to work on Friday. I work nights, so I got to work about 3:10PM and parked, everything was fine. I got out of work at midnight and the engine is frozen solid. I didn't know that at the time, all I knew was that it wouldn't crank. I tried jump starting in and that didn't work either. Got a ride home and came back Saturday afternoon, after 8" of snow. Tried again to jump it with the same results. Gave up and had it towed to the local European performance specialist. They're great, I've been going there for years. The 100% do not bullshit you. They were rather stumped, but eventually removed the plugs and got water to squirt out. Then they drained "a lot" of water from the crankcase. They weren't sure of the exact amount, but more than a cup, probably about two was their guess. The car is fine now.

However, most of the treads on this subject seem to think it's most likely to occur after long drives and immediate shutdowns. I drove 14 miles in 20 minutes and let the car idle for 5 minutes because I was early and didn't want to go inside and deal with the people on first shift. This, to me at least, makes the suggested remedies a bit questionable.

 

So one thing occurs to me.

When you have an air compressor (like for air tools, and other pneumatic applications) it's often needed to periodically drain out the condensed water that settles in the bottom of the tank.

A supercharger is more or less an air compressor.

And there's an interesting point raised in this article Winterize Your Air Compressor | Compressed Air System about the dew point of air. "When the temperature of compressed air or gas lowers to a certain level of coldness – generally referred to as the dew point – where it can no longer hold vapor, the vapor turns to liquid, which in turn causes condensation on a compressor system."

So that's temperature, other thing to consider is vapour pressure.

When you compress air to a certain pressure, the moisture in the air changes from a gaseous state to a liquid state. Same thing happens when you reduce the pressure (i.e. a vacuum) then you can make water boil at room temperature; turning to gas.

So there's a few things to consider here...

Is the compression of the super-cold air by the supercharger causing condensation to build up in the intake?

Is the warming of the cold air by the supercharger and intercooler causing the condensation to form?

I don't think it's temperature alone, otherwise you would see this happening on naturally aspirated cars.

I think it's a combination of pressure and temperature...

If you're driving cautiously through snow and slush, you're not really getting on boost at high revs which makes the charge air hot, but there is still going to be a certain amount of compression happening, even with the bypass valve open...

 

Engine running, there's some amount of vacuum so you'd expect the air to dump some water (small amount, when so cold) all the time. It must not normally freeze or we'd have had every cold-region SC engine (maybe every NA one too) with this every year.

With the SC not really doing much (bypassed) it's not altering the vacuum but does provide extra intake where water might condense out and maybe freeze. OK, so that may be why NA engines don't suffer.

A cup of water is a lot.

What's changed? Why now?

Old cars? (why would it matter?)

Very odd atmospheric conditions? (are they?)

Engine cover removed? (Does it matter? Maybe)

 

Thanks for the great additional info. Very helpful.

Most of the cases reported so far have been of a long drive, no idling period type so I presumed those conditions were the most likely to induce the issue. Seems not. I wonder if you'd recall the driving cycle(s) of the car prior to the final one where the engine locked up. Gradual build up of ice with no melting period?

 

The age of the cars could be a factor. More wear means lower compression, for example. Not sure how that would fit into the equation, but it's one change from new. EGR passages are also prone to carbon clogging with age, so that's another age-related variable.

I bet the lack of the engine cover is another variable. That would change the underhood heat distribution, both while driving and at rest.