Is the Tail wagging the Dog

[Killerbees]

I am working on an interesting problem with a fleet of diesel Pickups that tow for a living. The problem is they overheat. I am working on a aux cooler that will expand the heat rejection capacity.

The existing oem coolant-oil heat exchanger allows oil to preceed coolant temps by 20-40 degrees F at lower temps. The hard working vehicle sees a steady increase in ECT untill overheat in some conditions. The oil has been temped at over 340 at the filter near the boilover point of 260 ECT, 270 degrees at 230 ECT. I must have coolant boiling in the cooler! Pressure goes from normal of 55-60 psi, to 30 psi, disturbing image.

Typically a 15W40 is used, often synthetic. I am interested in understanding more about lubrication problems at these temps, specifically, if the hotter oil likely creates yet more heat (lubrication loss), in a cyclically deteriorating thermal loop. And also, how the reduced viscosity, affects distribution of flow within the passages.

Seems the oil is more of a coolant, than on many vehicles. It has under piston squirters, vital to cooling. I read one article that suggested that oil can move as much as 25% of the engines convection needs.

A few details: 2 thermostats, from 185 crack to 210 full open (bypass closed). Coolant flow is roughly 50-70 GPM, rpm dependent, oil (10 quarts) is around 10-12 gpm, a high flow system.

[ December 16, 2005, 10:43 AM: Message edited by: Killerbees ]

 

[kanling]

Sounds like you are giving this a thorough analysis. You are right that the oil makes a significant contribution to engine cooling.

For the oil, you could install an external oil cooler and install the biggest possible oil filter. That would give you better cooling and a larger oil volume to absorb the heat.

What trucks are these?

Geez, I'm also thinking of the transmission temps.

 

[Gary Allan]

I don't have a clue to your needs beyond bigger is always better in buffered cooling. I'm in the process of putting together multiple heat exchangers that will then be coupled to a thermostatically controlled airil heat exchanger ..but my application is not demanding. I'm doing it for the novelty of it. I should be able to unload the rad while keeping the oil temp pretty well dialed in @ 195-200F.

...but I have a question..

quote:

---

The existing oem coolant-oil heat exchanger allows oil to preceed coolant temps by 20-40 degrees F at lower temps.

---

Do you know the modality that the heat exchanger uses to allow this to occur? I can only limit the exchange to a preset limit. That is, I can inhibit oil cooling below 180F (or whatever I order the thermostat at) ..but I can't manage to allow a 40F differential indexed for anything. The only way I could manage that is to have too small an exchanger and run under extreme stress on the oil ..so that they could never match each other. Your description appears to simulate this under no load conditions or at least at, as you say, cooler temps.

The current NASCAR engine builder theory puts the cooling figure at around 40%.

 

[BlueWorld]

If this is a consistent problem it's pretty obvious whoever made the lease decision grossly under-speced the base powertrain.

You can find an oil that will take the temps, but if you don't upgrade the oil cooler(s) and increase oil capacity that's not going to help much.

An oil can be an effective coolant, but you need something to transfer the heat to.

Ditto on the trans temp question.

 

[Killerbees]

Thanks for the comments.

A little more. GM Duramax-Allison. Trans temps are well handled in 2 stage, radiator, then stack mounted cooler. They do climb with ECT's, a symptom of the rad load as expected. Within normal parameters, tranny temps are balanced nicely, typically under 190, but climb to 240 or so with the conditions described above. These are turbo-diesels, with a huge CAC that raises ambient 20+ degrees F, pre-radiator. The condenser sits in front of that, another 25 degree rise. On a hot day, it is a task to cool the rad. One of the earlier efforts focused on airflow and CAI with some limited success.

I have little information on the effectiveness of the oem cooler unfortunately, though I do like the quick oil heatup, to operating temps.

I have more-or-less estimated heat rejection needs at 250K BTU/HR, with capacity at around 200K. So I figure the right direction to go, with my hottest fluid being oil, is further system expansion, to the tune of 50K air-oil exchange. Now I need to implement it.

One thing I want to avoid, is having the oil cooler fighting the coolant stats. I need a little guidance to control oil temps thermostatically, to regulate oil under 230, yet never overcooled. The trucks like to run at 210 till rejection underwhelms heat creation.

 

[Killerbees]

I have looked into the NASCAR "brick" type coolers, that would handle 50K btu, but they are expensive, fluidyne comes to mind. One I looked at is 4"x4"x28" Any other sources of these radiator look-alikes?

 

[Killerbees]

I may have been misleading. The oil does not warm up ahead of coolant. It has the common characteristic curve of lagging the coolant. When under load, the oil pulls out in front by a large margin, as much as 80 degrees F. it appears as though, oil rise is pulling the coolant up. Sorry for the confusion.

I would like to use a sandwich adapter, but have an issue to address. Can I get one that will flow 10 gpm, without triggering the various bypasses? Obviously the more flow I can establish in the cooler, the better my exchange will be.

Also am concerned about the various thermostat options. I am not thrilled about a 10% cold bypass on an oversized cooler. That may be an issue in cold weather. Which thermostats have the least amount of cold bypass?

 

[Ken2]

I'd get a fan-cooled external oil cooler with a thermo-switch on the fan. I'd remove the oil lines from the radiator and just run them to the new oil cooler. Permacool has a thermostatic bypass valve for the cold oil to bypass the cooler.

I'd be sure the radiator and rest of the cooling system are 100%. I'd reduce your antifreeze concentration to 40% and add a product like Redline Water Wetter. I'd consider adding a substantial electric fan to the front of the radiator if the overheating happens during idling or slow speed operation.

I'd use nothing but 5W-40 synthetic oil. That will heat a bit less and will not be damaged by the heat as readily as conventional 15W-40 oil.

I'd also see if the ATF could be externally cooled and that removed from the radiator. (Just re-route the cooling lines to the new cooler and leave the radiator with unconnected cooler fittings).

Have you checked with a GM truck dealership, one that specializes in medium duty commercial trucks with this engine?


Ken

 

[Gary Allan]

Mocal makes this thermostat. You can order your desired temp. It can be had in fairly large line sizes 1/2", 5/8", 3/4" (8,10,12AN) ..but 1/2" should be enough for your needs, IMHO.

Since you didn't give a year and a model (I assumed a 3500 chassis) I had a hard time getting a filter number puked out of the Wix application guide. If I "guessed" correctly (it kept eliminating things I had already selected when I selected other things i.e. year, engine, model) you still have the 13/16 thread (this doesn't sound correct) filter. That would mean that you could use a Mocal sandwich, as well. 13/16-16 is the largest SAE thread ..with 18, 20, and 22 mm sizes for metric.

It has 1/2" ports. I don't know if it has an internal bypass. It uses a "waxstat" with a limit of 140C/284F ..it damages the waxstat above that temp (the unit is servicable) ...so cooling must be adaquate before adding this feature.

Hayden makes one ..but it is a 180F sandwich. It uses a bimetal spring to cover a port that bypasses the cooler circuit (or whatever you have hooked to the ports).

Permacool's sandwich doesn't come with an integrated thermostat. I has a pressure relief that, I believe, has a 2psi breaking threshold. It only has 3/8" ports ..but that really doesn't present any major issue in terms of volume capacity. Their thermostat is the one that bleeds 10% flow through the cooler continuously.

Any increase in sump size (with, for example, remote filters) will not lower oil temps. It will merely delay transitions in temp ..perhaps dampen would be a better term.

You should have ample room to use rail coolers of substantial size if frontal real estate is in short supply.

Since it appears that you're peaked out on rad sizing, I would increase the size of (or add auxillary) oil:water heat exchanger and then get the most square" of oil cooling that can be mounted to the vehicle.

If the duration of the event is short enough, then adding mulitple high volume filters might shave the extremes due to having more to heat.

 

[MolaKule]

I'm with Ken2.

Offboard and install separate oil coolers and have them each controlled by their own electric thermostatic fan system. I don't see how you could overcool the oil this way.

 

[kanling]

I also like Ken's suggestion to cut the antifreeze percentage in the coolant. You'll have more heat capacity that way. (Just change it a little more often to make up for it).

 

[the_oil_dealer]

yup, water wetter / borate nitrate and modified cooling system seems to be in order. Tow truckers make a KILLING, it shoudl be nooo problem for ya

 

[jsharp]

Adding an additional air to oil cooler - It would be a good idea to find a different airstream for the oil cooler instead of just stacking it in front of the radiator. Stacking them puts heat pulled out by the oil cooler back into the cooling system via the radiator and that's a problem you already have...

 

[1sttruck]

When I looked into it a couple of years ago it seems that the diesel engines in the Ford and Dodge pickups are used all the way up to class 8 vehicles (some drivers have said that you don't see those engines used much above 30k lbs), while GM switches to a larger 8L inline 6 above class 5. The torque wars is taking it's toll on soem of the designs.

 

[Killerbees]

The same cooling system is in the medium duties FWIW, they struggle also.

I am with Jsharp, I will not dispense into the stack, and there is room and sufficient static pressure to locate a cooler underneath in the free stream, so I am pursuing that. A fanned cooler is probably out due to complexity and cost. Kinetic energy is what I plan to use, and will move more air anyway. I just need to resolve my overcooling concern.

I have looked at all the sandwich adapters, and spoke to Eric at Mocal about a newer high flow application that hasn't been released yet. I may try to test one.

I will probably try to control to 200 F. Does the sandwich adapter flow much below stat temps? I really need to minimize that for warm-ups in cold weather I think.

 

[Gary Allan]

Does the sandwich adapter flow much below stat temps? I really need to minimize that for warm-ups in cold weather I think.

On which sandwich adapter? I would think that Eric already told you about the Mocal(s). A Hayden bypasses a variable % depending on visc/temp. A Permacool has no thermostatic element to it ..other then thick oil will open its bypass if the cooler presents too much pressure differential.

I think that your issue with handling the higher end problems take precedence over a few more minutes, more or less, to warm up.

I can understand the "simple" part of it in your equation being a fleet ..but you're in a ****ed if you do ..****ed if you don't situation in terms of cost. The cost of not doing it surely outweighs the expense by years of service life.

I don't think that you need any "high flow" thing designed for dry sump operations in race cars. 1/2" lines are not taxed with 10-12 gpm of flow.

 

[Steve S]

Probably needs a bigger radiator ,G.M.products don't give the buyers much for their money. Also are the drivers properly operating the vehicles?

 

[Killerbees]

As I like to say, in a 4 layer stack, the only thing wrong with the radiator is the intercooler. And the condenser. and the transmission cooler! LOL

It is the perfect storm that I am fixing for, the guy running over CGVW, up 8% on hot days, with high drag loads. His oil gets to 300 degrees regularly.

Thank you for all the help up to this point.

Do these sandwich stats have any record of reliability issues? I assume wax pellet is important to stick with.

Gary, the pics of the oil-coolant exchangers you show. Those are not going to expand capacity correct? If I understand what you are saying, then I should get the oil as cool as possible with a cooler, send it to exchange with the coolant, thereby providing the greatest benefit for capacity expansion, for the coolant. Is that what you are saying?

Interesting idea.

 

[Gary Allan]

Yes, essentially you're in a pickle with the radiator as well as the oil. You can't expand your radiator capacity due to everything that has to be there. Sure you can probably unload some of the btu's dumped in front ..but the rad is still going to be there ..and probably everything else too.

So you use your oil as an additional dumping point for excess heat. You can expand your oil cooling capacity quite a bit and fairly cheaply (with simplicity and high reliability). Once you have full control of your oil temp, you merely shunt more coolant heat to the oil via larger oil:water heat exchangers.

I don't have any situation like yours ..but I'm playing with this anyway. I like having lots of "insult reserve" designed into the cooling/lubrication package. I want my oil to gravitate to normalized coolant temps (around 100C) ..and I want the cooling system to have as much untapped capacity as possible. It's a win-win.

The only way that I would run into "trouble" is if I excessively cooled my oil to 180F (I don't have a higher spec'd thermostat) and my bypassed cooling circuit shunted too much heat from my engine and maintained it in a fuel enrichment state. It could also, if over done, slow my initial warm up. I naturaly wouldn't worry about that aspect of it ..if I was loaded to the gills and working the engine as full time as possible to squeeze the $$ out of it.

 

[Killerbees]

I like this.

Now if I could just find a cooler source for 50K BTU/HR at a reasonable price.

Found one guy in australia who can make them (NASCAR type coolers, 3.5" deep).