Rob Edwards

So we found a good way to stress-test a 928 radiator at Sharktoberfest- the method involves tossing the keys to your car to half a dozen people and redlining the car up and down the street before you're sure the thermostat is fully open....

After the last test-drive, the car came back trailing a small puddle of coolant off the passenger side end tank, not catastrophic, but a seep all along the length of the tank. Bit of a bummer given this is a dual cooler radiator with less than 1500 miles on it.

Greg pulled it yesterday and took it to his radiator guy, who diagnosed an overpressure-induced failure of the gasket on the passenger end tank. He said the crimps were stretched up on both end tanks, worse on the passenger side. Pulled the PS tank, new gasket, recrimped both ends, good as new. $177 all in. Easy peasy.




So having a look at the factory coolant flow diagram, if the thermostat is completely closed, the pump is recirculating coolant through the block, into the water crossover, and then either back through the pump or out the deadheaded radiator circuit. I’d guess the cross sectional area of the upper radiator hose outlet is greater than the sum of the cross-sections of:

1. the overflow hose on the DS rad end tank to reservoir
2. The overflow hose on the water crossover-to-the-reservoir, and
3. The bypass passage in the rear T-stat housing of the water crossover that feeds the pump

Obviously I’ve never measured, but I’d guess the WP is spinning about the same speed as the crank (?)

So 6000 rpm of WP output is creating the greatest pressure in the deadheaded radiator hose, and there is insufficient ‘alternative’ flow within the engine to mitigate that pressure. (Heater valve is present but is closed, no circulation through the heater core back to the res...) I'm sure the overflow hoses were jetting coolant back to the reservoir, but perhaps not enough to increase the pressure there so the radiator cap didn't blow off pressure?

Any of you fluid dynamicists wanna weigh in on this hypothesis?

Lizard928

Bummer!

But I have to admit, the car was a blast to drive!

One point of interest, while the rad only had 1500 miles on it, how long had it been in storage?
it's possible that the seals had partially dried up before you even got it.

Rob Edwards

Not a clue how old it is, it was one of the $800 specials that Roger did back in 2/11, it sat for a year before I even put it in the car in 2/12. And I still hadn't managed to install Greg's trio of oil cooler hoses that required the radiator swap in the first place, they've been sitting in the garage for 2+ years. Just as well, made it easier to pull the rad...



Might have been a partially dried out seal, might have been incompletely warmed up, whatever, I'm not worried about it. Perhaps we'll learn something about the coolant flow in these engiens in the process. Besides, I easily had $177 worth of fun on Saturday!

Lizard928

Oh I will most certainly agree with that last statement you made!

If we did that on a road like you did up here. There would damn near be a swat team surrounding us in minutes.

Rob Edwards

Did what?

Bigfoot928

did you set up a collection bucket for the tires and fuel used? You are a better man than I am if you didn't have a collection bucket....

Rob Edwards

Nah, the SEG's on everyones' faces post-cruise was payment enough.

GregBBRD

The "old school" radiator repair guy I use said that the tank had been lifted off of the seal from overpressure. Actually had "bent" the tabs out, when this happened.

It was so severely "lifted" that he did not feel that he could just "push" it back down and re-crimp it, but needed to actually remove the tank and replace the seal.

His exact comment was: "Well, you know it didn't leave the factory with the tank like this."

Turned out that the "cold side" had also lifted some, but he was able to just reseat that tank and re-crimp.

I guess Rob needs to make sure the thermostat is actually open, before spinning it to 7,500......and then make sure it is still open, before everyone that can turn the key beats on it like a redneck beats on his wife.

And it is simply an amazingly fun thing to beat on. I did a 2,000 rpm in 3rd gear to 7,500 "romp", with Roger in the car.....that had us all laughing, out loud. It didn't take many seconds or much road to accomplish this....even with the tires spinning some, at 4500!

It is a beast!

soontobered84

So Greg, when do you start working on Roger's stroker? Or are you already?

GregBBRD

I'm really excited about trying this manifold on a "Roger box".

And I did add in the extra pieces inside his transmission, when I rebuilt it, that will make this possible.....

Randy V

How much time will it take to return to stock configuration for biennial SoCal smog inspections?

That's one of the reasons I've stayed away from modified induction on my car.

PorKen

I reckon one of the two thermostat springs is for overpressure.

I noticed on my '88 that the aftermarket t-stat that I replaced had a much higher overpressure spring tension.
At the time, I thought the higher overpressure limit might not be a good thing.


OEM, left, also has a much larger seal disc = easier to push/keep open?

Lizard928

Ken,

Did you make it home without any tickets?

There were LOADS of revenue collectors out on the way home. I had a V1 which saved a bunch...... But I know you didnt have anything in your car........

PorKen

No probs. I have a Passport 8500 X50 (black) mounted just about the dash.

All the bears I saw had their KAs on full time, so it was pretty uneventful.

Except for the occasional 1/4 mile pass to clear slowskis, I went just 10-over most of the way, anyway.

Speedtoys

The revenue collectors, are there collecting from the revenue donators.


Two way street there.


I counted probly 6 in my 350mi drive home.