Towing Mods: how hot can we safely get a D24T?
 

In one month I'm towing a 3,000lb Catalina 22 sailboat over the infamous "grapevine" mountain pass in southern california, with a peak altitude of 4,160 ft. My goal is to prepare my 1984 760 diesel in advance such that my engine survives this difficult task. My brakes and suspension are already heavily upgraded, so I'm *only* worried about engine cooling issues here. The boat trailer also has excellent and brand new brakes. The car is also factory rated for towing this weight.

Anchored off Santa Cruz Island this January, after towing to the launch ramp with a 740 Turbo:
http://d24t.com/attachment.php?attac...1&d=1374605491

Goals
-calculate EXACTLY how hot she can run, and monitor closely such that I pull over before damage occurs
-modify the car to maximize the margin of safety
-plan a safe driving strategy
-have an awesome trip sailing with my dad in the California Delta

Engineering starting premise
The engine will be fine as long as the coolant remains in the liquid state. Therefore, I will estimate as accurately as possible the true boiling point, and not allow the engine to get within 5 degrees Celsius of this value.

Please no comments about how I'm "over-thinking this." I'm an engineer, and I enjoy solving problems this way.

Cooling concentration and pressure considerations

I tested my cooling system for pressure handling with a bicycle pump, and tested the concentration of antifreeze with a float hydrometer.

It turns out the cap is opening at 10psi, and I'm at 30% antifreeze. Both are way below spec. My Zerex g-05 ethylene glycol based coolant is rated to boil at 128C with 15psi of head pressure at a 50/50 ratio.

To raise the concentration, I'm going to replace coolant with pure antifreeze according to this formula:

(0.3(3-a)+a)/3=0.5
where a = antifreeze volume replacing current fluid
0.3 = current concentration
3 gal = system volume
0.5 = desired concentration

This suggests I need to replace 0.86 gallons of coolant with pure antifreeze to get up to a 50% mixture. To raise the opening pressure, I ordered a new 16psi radiator cap.

I will also be cleaning out the radiator with degreaser, as my radiator is still clogged with oil from the oil cooler blowing. I'll also be adding a VERY VERY large external oil cooler using aircraft grade hardware.

I still need to open up some basic chemistry textbooks to estimate my final boiling point. I'll be using a 16 psi radiator cap, but on the mountain pass at 4,160 ft I'll be at 12.7 psi ambient pressure (2.1psi below sea level pressure) so I need to consider this factor as well. I'm guessing the boiling point will be somewhere around 125C, allowing me to safely run up to 120C.

Edit: Boiling point estimate
Based on this PDF, a good rule of thumb is that 1 psi of pressure raises the boiling point by 3 degrees F. Therefore, based on my coolant specs I expect my boiling point will be about 127C at 4,160 ft with a 16psi cap and a 50/50 mixture. Therefore, I can safely run up to 122C, and will set an audible alarm at 120C for the climb.

Driving Plan

I'll try to hit the pass at the coldest possible time, which should also have the least traffic. This means hitting the summit right before sunrise, which means between 5am and 6am where it should be under 70F even on the hottest august days.

In a reply on my "Ebay radiator" post, 745turbogreasel said to us 1/4 box of Cascade dishwashing detergent to clean out the radiator. I had used Tide in the past on my 1957 Mercedes 180D and it worked fairly well. It did take several flushes with clean water to get all the soap out. I removed the thermostat to make sure the flow was good.

The oil cooler is an excellent idea. I put a small Volvo turbo oil cooler on, using the Volvo sandwich plate attached below the oil to water cooler so I get the benefit of the heat exchanger plus the air to oil cooler.

I'm thinking if this engine can pull a Pinzgauer it can handle the boat.

I already flushed about 10 times with laundry soap, and it now drains clear... but it seems to mysteriously still run warmer than before! It's a 11 month old Nissens radiator. I'm going to try removing it from the car, and soaking internally with purple degreaser as commonly done with Volvo intercoolers. I'll also be cleaning out a used mid-90s Volvo intercooler to install at the same time.

Any idea what those things weigh? I'd imagine the Pinz has lower gears and a vastly superior cooling system. I've come to the conclusion that the D24T Volvo cooling system is crappy for some reason, because it runs much hotter uphill yet makes much less horsepower than the Volvo red block engines in the same car. Maybe the red blocks flow water at a higher rate or something. Even with a brand new radiator, tropical fan clutch, new thermostat, and cast iron water pump I can hit 116C uphill with my D24T. A stock red block turbo making 50% more horsepower with a smaller radiator and a less efficient engine would never get over 100C under the same conditions. The same tropical fan clutch also kicks in at much lower temps on the red block despite the same thermostat opening temps, suggesting much better heat transfer to the radiator in the red block.

Any pics of your car? The ponton is one of my favorite cars, I've always wanted one!

I find if I drive to keep the EGT below 1250, the temp behaves quite nicely no matter how long a hill I'm pulling.

IMO gauge sender placement and something in the design not allowing the head to reject heat fast enough are working against us.I think having the cooling system configured in such a way as to have a constant out flow at the back of the head may help.

As far as the car half of the cooling system, it's the same as a 960 which works great, even with a v8.

Meth injection to keep EGT down might be an effective approach.

Interesting, I've had an EGT gauge installed for years but haven't drilled and tapped for the sensor. I'll go ahead and do that this weekend. Is a metal plate over the EGR port an okay mount location?

My temp sensor is actually an aftermarket digital one mounted to a vacuum pump bolt. My handheld infared thermometer says that the head has relatively uniform temps, always at the same level as what the digital one on the vacuum pump bolt reads.

1957 Mercedes 180D pictures.
 

The 180D is the first diesel I started working on about 7 years ago and it's the one that got me hooked on diesels.

I only have a few pictures of this car but it gives you an idea of the before and after. It's not perfect but it's my daily driver and is perfect for getting around town and for short trips around Reno. I have driven it over Donner Pass on I-80 to Sacramento and it never went slower than 50 mph in the steepest sections. On flat ground I can run 65 - 70 mph all day long!!

http://i1180.photobucket.com/albums/...dwithRiley.jpg

http://i1180.photobucket.com/albums/...ps6899d705.jpg

Beautiful. I think it's a close tie between a matte black Ponton and the 300 Adenauer for classiest looking car ever made. In my book, yours wins since it's also diesel. The performance doesn't sound too bad either, it's a rocketship compared to my Isuzu Trooper which takes similar passes at only 25mph. I've done Donner Pass only once, in a 1983 760 Diesel but remember that it was formidable- very steep and high altitude.

If you ever want to sell it contact me!

I'd think so, but I used a non EGR manifold.
20 minutes well spent for sure, it helps you track heat generation and economy in real time.