6.9 in a bus needs radiator. Upgrades?

Luke_IDI

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First post on Oilburners, though have been lurking for a year or so since I bought this school bus. It's a 1987 International S1700 with a n/a 6.9 in front of an Allison AT545 transmission. The bus only has 56,000 miles on it, but the enormous copper-brass radiator (probably original) is totally rotten and I am fed up with chasing leaks. These radiators are upwards of $700, and I want to be sure I get the right one for my future needs. I'm here to ask for advice on how much cooling capacity I might need to cool my IDI. It's currently bone stock, but I have an ATS 088 turbo kit I'll be installing at some point, and would like to be able to use this platform to play around with turbos generally in the future. My performance improvement goals will be geared toward efficiency, while also producing enough power to comfortably cruise this thing at 65 or 70 mph (a rear end re-gear is definitely in the plans). The radiator I currently have is this one:


As I have been googling replacements, I find that many of the later model buses have split radiators where an intercooler would fill the other side of the radiator frame, like this one, for example:


Any idea whether a split radiator would be sufficient? How many rows I would need in a split configuration? I like the idea of being able to place an intercooler next to the radiator core in this way, as getting intercooler piping to run in front of the radiator would actually require cutting away some of the fiberglass cowl/modifying the grill of the bus (which is surprising, given the amount of room everywhere else, but true). Moving the rad support back would be a huge project as it is entangled with the front leaf spring mount. I can't imagine these split radiators would not have enough cooling capacity, as it seems they are specified for buses with larger engines, e.g. a DT466. But I'm on a limited budget and need to get this right the first time. Thoughts?

Thanks,

Luke

Edit: The AT545 is a notorious heat producer, and though I plan to add an external oil to air cooler before the oil to water cooler in the radiator, I need to factor this into my decision as well.
 

danno

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I’m running a champion aluminum radiator like many in the forums and I have no cooling problems anymore. I’m running a stock turbo from a ‘93 IDIT on my ‘86 with some intake mods and a 4” exhaust.
 

Big Bart

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First post on Oilburners, though have been lurking for a year or so since I bought this school bus. It's a 1987 International S1700 with a n/a 6.9 in front of an Allison AT545 transmission. The bus only has 56,000 miles on it, but the enormous copper-brass radiator (probably original) is totally rotten and I am fed up with chasing leaks. These radiators are upwards of $700, and I want to be sure I get the right one for my future needs. I'm here to ask for advice on how much cooling capacity I might need to cool my IDI. It's currently bone stock, but I have an ATS 088 turbo kit I'll be installing at some point, and would like to be able to use this platform to play around with turbos generally in the future. My performance improvement goals will be geared toward efficiency, while also producing enough power to comfortably cruise this thing at 65 or 70 mph (a rear end re-gear is definitely in the plans). The radiator I currently have is this one:


As I have been googling replacements, I find that many of the later model buses have split radiators where an intercooler would fill the other side of the radiator frame, like this one, for example:


Any idea whether a split radiator would be sufficient? How many rows I would need in a split configuration? I like the idea of being able to place an intercooler next to the radiator core in this way, as getting intercooler piping to run in front of the radiator would actually require cutting away some of the fiberglass cowl/modifying the grill of the bus (which is surprising, given the amount of room everywhere else, but true). Moving the rad support back would be a huge project as it is entangled with the front leaf spring mount. I can't imagine these split radiators would not have enough cooling capacity, as it seems they are specified for buses with larger engines, e.g. a DT466. But I'm on a limited budget and need to get this right the first time. Thoughts?

Thanks,

Luke

Edit: The AT545 is a notorious heat producer, and though I plan to add an external oil to air cooler before the oil to water cooler in the radiator, I need to factor this into my decision as well.
Keep researching but here are some thoughts.

1) Some folks who put on intercoolers on their IDI trucks have had issues. Meaning the air going in the engine was cooler at the cost of heating up the radiator. Causing heat issues when climbing hills towing. For some it was a problem.
2) These trucks have large radiators but really need the capacity for hill climbing while towing. Cutting the cooling in half may be problematic.
3) Folks without a intercooler are not having issues but watch their EGT’s and let up once they get to 1,100*. Keep in mind most are only boosting 8-12psi so intercooling is not required and has less effect than say at 12-18psi of boost with twin turbos down at the exhaust manifolds. Also keep in mind the engine compartment is quite large, the grill and radiator are quite large, and there is a lot of space around the exhaust. So your engine can shed heat faster than a new truck with a smaller compartment that is stuffed to the gills.

The challenge
1) Can you run a heavy and loaded bus on half a radiator?
2) Will intercooling make a substantial temp difference at 8-12 psi?
3) Can you install the intercooler so it does not send hot air at or block air to the radiator.

With so many on this site not intercooling and not overheating, I would choose a bigger radiator over an intercooler. Then if I had issues with over heating revisit the intercooler.
 

Black dawg

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Keep researching but here are some thoughts.

3) Folks without a intercooler are not having issues but watch their EGT’s and let up once they get to 1,100*. Keep in mind most are only boosting 8-12psi so intercooling is not required and has less effect than say at 12-18psi of boost with twin turbos down at the exhaust manifolds. Also keep in mind the engine compartment is quite large, the grill and radiator are quite large, and there is a lot of space around the exhaust. So your engine can shed heat faster than a new truck with a smaller compartment that is stuffed to the gills.

The challenge
1) Can you run a heavy and loaded bus on half a radiator?
2) Will intercooling make a substantial temp difference at 8-12 psi?
3) Can you install the intercooler so it does not send hot air at or block air to the radiator.

With so many on this site not intercooling and not overheating, I would choose a bigger radiator over an intercooler. Then if I had issues with over heating revisit the intercooler.

This is not what I have seen over many trucks I have owned and been around/worked on.
A turbo 7.3 with the fuel maxed out on a stock pump will have heating issues.

Intercooler does add to this, with reducing airflow to the radiator, and increasing air temperature to the radiator. Intercooling these does make a substantial power difference, even with the old aftermarket kits at 15psi or less.

To the OP, I would run a full size radiator, and then add the intercooler later if decided.
 

Cubey

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1) Some folks who put on intercoolers on their IDI trucks have had issues. Meaning the air going in the engine was cooler at the cost of heating up the radiator. Causing heat issues when climbing hills towing. For some it was a problem.

For what it's worth, the 3x larger trans cooler I put on my RV hasn't really hurt coolant temps. Now, AC maybe? Not sure if it's the bigger trans cooler heating up the condenser more, or just the AC system running low, but it was blowing a bit cool the other day but not super cold. I need to check the AC system pressure since it's been about 14 months since I charged it from nearly empty with store bought cans and a single hose filler/gauge.
 

Booyah45828

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Run the full size radiator.

Those half and half jobs are marginal at best on the buses they're on. The IDI platform dumps a lot more heat into the cooling system, compared to a DI design. And all of the DI engines that have that half and half setup are borderline overheating in my experience. Another thing those half/half jobs struggle with is fan clutches, as the intercooler side won't allow the clutch's temp spring to see an accurate coolant temp. So if you make the mistake of installing one of those half/half jobs, run some self tappers through your fan clutch to lock it solid.

An AT545 dumps an enormous amount of heat into the radiator. Unless the cooler your installing is the size of the radiator, you can't eliminate the radiator's atf loop. Install a temp gauge on the trans to see if more fluid cooling is needed, before going through the hassle of installing another cooler. Most coolers that are available are for light trucks/passenger cars and don't flow near enough fluid.

Like you, my idi is in my bus, a 1984 s1700 6.9idi/at545. I've got the parts of a rayjay turbo kit that I'm going to install with a garrett tp38. The plan is to use an air-water intercooler on it, as it's easier to route a couple hoses than 3" turbo pipes. I also plan on using the same coolant as the engine, pulling it from the bottom of the block, running it through a 2nd radiator, through the intercooler, and then back into the water pump.
 

Luke_IDI

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Run the full size radiator.

Those half and half jobs are marginal at best on the buses they're on. The IDI platform dumps a lot more heat into the cooling system, compared to a DI design. And all of the DI engines that have that half and half setup are borderline overheating in my experience. Another thing those half/half jobs struggle with is fan clutches, as the intercooler side won't allow the clutch's temp spring to see an accurate coolant temp. So if you make the mistake of installing one of those half/half jobs, run some self tappers through your fan clutch to lock it solid.

An AT545 dumps an enormous amount of heat into the radiator. Unless the cooler your installing is the size of the radiator, you can't eliminate the radiator's atf loop. Install a temp gauge on the trans to see if more fluid cooling is needed, before going through the hassle of installing another cooler. Most coolers that are available are for light trucks/passenger cars and don't flow near enough fluid.

Like you, my idi is in my bus, a 1984 s1700 6.9idi/at545. I've got the parts of a rayjay turbo kit that I'm going to install with a garrett tp38. The plan is to use an air-water intercooler on it, as it's easier to route a couple hoses than 3" turbo pipes. I also plan on using the same coolant as the engine, pulling it from the bottom of the block, running it through a 2nd radiator, through the intercooler, and then back into the water pump.

Thanks for the thoughtful responses everyone. Also thanks Booyah for the experience on split radiators in buses specifically. I forgot I had seen your build thread over on the skoolie site. Good point about an intercooler affecting operation of the fan clutch--I hadn't thought of that. I got a quote for $900 for a drop-in 4-row copper brass from Holst Truck Parts out of Idaho, the best price I've seen after several quotes.

The bus sat for years before we bought it. The radiator that's in there now is a 2-row. It stayed cool for a few hundred miles (cruising on the highway at about 55mph usually, 2800rpms or so, currently 5.57 gears in the rear end), and then began to overheat. After going through everything else in the cooling system (multiple cooling system flushes, pulled heads, replaced cracked head, oil cooler cleaned out and new o-rings installed--the cooling system was an absolute mess of rust and sludge), I unsoldered the radiator tanks to find most of the tubes completely plugged with mineral deposits and more rusty sludge. Rodded out the tubes and resoldered. It stays cool again now, but the leaks have started springing up again, so time to replace. I'm guessing that 4-row should up the cooling capacity considerably.

I plan to install a trans temp gauge when I change the ATF--next on the list of maintenance items. Also, no plans to eliminate the trans cooling loop in the radiator, just add an auxiliary air to oil cooler if needed before the radiator if necessary, but I doubt I will see that need with the new radiator. It should be said that I would love to ditch this AT545 for something with lockup one of these days, but that is probably a long way off. For now I just want to get it driving reliably so we can focus on the interior.

I will keep the air to water intercooler idea in mind, too. What is the advantage to running a second radiator for your intercooler loop? Are you thinking your main radiator will not have enough cooling capacity to cool your intercooler? I wonder if this monster 4-row radiator I am acquiring will have enough excess capacity to avoid running a second radiator if I ended up going with such a setup in the future.

Btw Booyah, what is your rear end ratio? Also, do you plan to post your turbo install on your skoolie thread or do you have an engine tech thread over here?
 

Booyah45828

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New vs old radiator. The cooling ability depends on the size of the tubes as much as the count. You'll gain a little more surface area internally due to more tubes, but if it's still a 2" thick core, it's still a 2" thick core. TBH fin count and spacing has as much or more to do with radiator efficiency as tube count does.

If the 4 row fits size wise, it will likely be fine. I've never had overheating issues with mine.

I suggest that you be 100% sure your modulator is adjusted on your trans, as it being out will lead to a quick trans death. A failed modulator is where 99% of the bad rep for the at545 comes from. Mine is adjusted under the dash on the throttle pedal, I can go through the adjustment steps if you'd like.

Reason for the 2nd radiator is for additional cooling before going into the intercooler. I want to use the engine water pump, to eliminate having to install a 2nd one for the intercooler, electric or otherwise. In order to do so, the water for the intercooler has to come from somewhere after the water pump, before the thermostat. With the source located there, and the engine at operating temp 195°F+, the coolant and intercooler won't be doing much air cooling. So running the coolant through an additional radiator will hopefully drop the coolant to a temp that allows it to actually do something in the intercooler. I originally considered pulling it from the bottom of the radiator, but if I'd do that, the thermostat would have to be open, or no water would flow through the intercooler. Which led me to pulling it from the bottom of the block.

With all that said, the electric intercooler pumps are very likely to prove reliable, and the few on here that use them haven't reported issues that I've seen. I was just after one less failure point.

My rear gear is a 5.57. With the pickup governor speed of 3500 rpm and 10r22.5 tires, I can go 70-75 foot to the floor. Granted, it takes a mile or more to get there, and any hill takes it away, but it's a true 75. We've gone on the interstate before and weren't run over. That interstate jaunt was also the hottest I've seen any of the temps, So I wouldn't do it regularly either.

Re-gearing with the 545 can be tricky, as you can lose a bunch of acceleration by doing so. And being an NA IDI, acceleration speed is nearly non-existent to begin with. My plan was to install a 2 speed rear end, OR to install an air shift spicer 4 speed auxiliary trans. Not to go faster, as 75 is fast enough, but to get the engine off redline. The problem is finding a 2 speed axle with air brakes and decent gearing has proven tough. Finding the aux. trans has proven equally as tough. I had at one time a manual shifted spicer unit, but sold it under the assumption I could find an air shift unit.

I bought a spare 7.3, as well as an mt643 for the bus. The plan was to rebuild both, match them together, turbo/intercool the engine with a bigger injection pump. Swap the new power unit into the bus, swap in the rear axle/aux transmission, possibly swap in a heavier front axle, and then roll with it.

What's stopping me is that I'm really considering selling the bus.

My friends have all bought campers(us too), so we no longer need to sleep 8+ people. I could gut the thing again, and make a "nice" skoolie out of it, but why? I'd be better off buying a different bus, and converting that. Plus, we already have a camper to camp in.

I put a lot into getting the bus set up to sleep a group of friends and be a mobile party spot, and I really don't want to undo that. I did none of it with the intentions of making money on the sale, but with the way bus prices are right now, I have a feeling I could sell it and come out ahead on the deal. To use the thing like I have, and then make a profit off it's sale, that's hard to pass up.
 

Isaac Ristow

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I had a 04 school bus I made to a rv had the t444e (7.3 psd) with a allison 2000 series. It had the side by side radiator/intercooler on it the original radiator was all rotted out I went to my buddys shop that hauls all the school bus racing buses away from the race truck and pulled the radiator out of a race bus that was basically new still and not damaged. I put a new fan clutch in and those two things cured my heating issue. If your putting a side by side radiator/intercooler in you'll need the frame for it I believe. My next thing is the first thing I would do is throw that at545 in the scrap pile and put a 5 speed in it or a mt643 allison.
 

franklin2

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Are there any of the old radiator guys left? I remember years ago if your tanks were good, they just ordered a new core and soldered your old tanks on to the new core to rebuild the radiator.
 

Booyah45828

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I had a 04 school bus I made to a rv had the t444e (7.3 psd) with a allison 2000 series. It had the side by side radiator/intercooler on it the original radiator was all rotted out I went to my buddys shop that hauls all the school bus racing buses away from the race truck and pulled the radiator out of a race bus that was basically new still and not damaged. I put a new fan clutch in and those two things cured my heating issue. If your putting a side by side radiator/intercooler in you'll need the frame for it I believe. My next thing is the first thing I would do is throw that at545 in the scrap pile and put a 5 speed in it or a mt643 allison.
Was the new radiator a side by side unit or full sized? I've read on people installing the full sized radiator/intercooler out of the 4900's into the 3800, but never seen it with my own eyes. Those half and half jobs always ran warm in my experience, especially in the summer.
 

Nero

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They do exist, you just have to search around. They're damn proud of their products though. I got a quote to recore my brass 4 core, and the estimate was $1200.
 

Booyah45828

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There's a place an hour away that still does brass radiator repairs. Last one I sent out for recore was a year or so ago for a stationary gen set, and it came to a little more then 2k. Not cheap, but the quality was 2nd to none and it works great. I see horror stories all the time from people who "upgrade" old brass radiators to alloy units. Makes you wonder if it's because it's aluminum, designed incorrectly, or if the radiator wasn't the issue.
 

Isaac Ristow

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Was the new radiator a side by side unit or full sized? I've read on people installing the full sized radiator/intercooler out of the 4900's into the 3800, but never seen it with my own eyes. Those half and half jobs always ran warm in my experience, especially in the summer.
Mine was side by side factory and I replaced it with a side by side in better shape from a different bus. I do still have my old one the whole frame and everything
 

teletech

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I'd run a full radiator, but I'd be scrounging for one from a junkyard and expect to pay $200-300.
Those AT545 is reliable and cheap, but it also might well be the very worst transmission you can own in terms of heat production and efficiency. A new rear-end will just make it slip more and make even more heat. My Allisons are all behind 6.6/7.3 I6 motors, but swapping to an MT-series auto (643) should be possible. If so it would reduce your heat load while increasing felt power and speed. I have two trucks that are very similar in size/weight and the main difference is AT vs. MT series transmission and the MT truck is quite a bit faster and gets much better mileage. Of course an MD transmission would give you O.D. as well, so that would save you the rearend swap.

I think this is with a DT motor, so your process will differ: https://tatumskoolie.wordpress.com/2016/05/05/swapping-allison-at545-to-allison-mt643/
 

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