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Discussion Starter · #1 ·
Hello,

Back in September 2021 I started rebuilding a 91.5 12 valve out of a D350 to put into a 2000 crew cab F350. I did a full rebuild on the engine and replaced just about everything. I will try to make a full list below. Just started driving it around earlier this month and its around 100 degrees down here in Texas. Whole ac system is new as well, running down the road with ac on seems to run around 180. This is using an autometer gauge with probe at rear of head. Once traffic slows down (normal rush hour traffic coming home from work) the gauge slowly starts rising getting up to 210 or more before speed picks up and slowly the temp starts to fall. I have swapped from a napa t stat to cummins 180 with no change at all- neither have temp swings like so many seem to have. Cummins t stat is installed with jiggle pins at 12 and 6 o clock. It gets up to 180 and stays there until it can't cool anymore and starts climbing. When it starts to get hot the upper and lower radiator hoses will be only have a delta T of 10-15 degrees (upper hose around 205 with lower around 189). I have tried 2 different fan clutches and am getting lockup now- verified by sound and feel of airflow being pulled through intercooler/rad. 7.3 fan shroud is installed trimmed down. I also have 2-12" pusher fans in the front bumper aimed at lower half of condenser (mounted before finding out first fan clutch wasn't locking up at idle). I installed another autometer temp sender at the front of head and hooked it to gauge to see if maybe the sender was off and it seems to read a little bit hotter as its right by the thermostat so I think the gauge is ok. Engine runs great otherwise but this has me stumped. The cooling stack is identical to the one in my 7.3 which will idle in 100+ weather with the A/C on indefinitely and never move the needle past 180 and that is with a 345K mile ac condenser that looks like hell vs all the new parts in this truck. The 7.3 is a stick so hard to compare idle egt vs the auto behind the cummins but the 7.3 will be around 300 egt at idle with the ac on where as the cummins will run 350 or so with ac off. Then once you put it in drive it will jump to 550 then add ac on and its over 600 and in drive at idle there is some visible black smoke out of the exhaust. Even in park it started creeping up to 210 the other day as I was hooking up my trailer though. I am running out of ideas, cooling systems are pretty simple lol and many people I have read about with the same or similar setups as well as the cummins in the dodges claim that they never budge over 180 either unless getting worked hard. The only thing left I can see is maybe the egts are too high? and the black smoke at idle in drive? overloading the cooling system at slow speeds? If anyone has any ideas or sees anything I might be missing I would really appreciate it. I am ready for a vacation from working on this thing for the last 9 months and would like to drive it to the beach as soon as I get this cooling problem fixed!



Things of note-
EGT at idle seem a lot higher than my 7.3.
In drive with ac on egts on the cummins are between 550-660
in drive at idle I have a bit of black smoke out the exhaust
fan seems to be pushing air OUT the sides of the shroud - I have already trimmed more shroud to let more air out the back (towards engine) but it still throws air out the small gap between shroud and radiator


Engine---91.5 12 Valve out of D350
VE pump rebuilt Farrell Injection
Duckys 5x12 injectors new bosch bodies
Hamilton 178/208 cam
Rebuilt HE351 with 12 volt on electronic wastegate making 30+ psi
cummins high volume low pressure lift pump
bored .020, New pistons, bearings, oil pump, valve job, 60lb springs
New cummins head bolts with slightly thicker Mahle head gasket accounting for piston protrusion
Many other things I am surely forgetting...

Cooling system-
New 7.3 radiator
(New A/C condenser and trans cooler in front and cleaned intercooler while it was out - no airflow blockage to radiator)
New 12 valve fan clutch, fan, and hub assembly
New gates water pump
New napa thermostat changed out to cummins 180 thermostat (currently running cummins)

Trans-
Fresh rebuild 4r100 from Dieselsite
billet triple disc converter, billet input, etc
trans cooler lines run to radiator first and then into huge 6.0 trans cooler in between condenser and intercooler
 

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I moved this to the Conversion Section.

The 12" cooling fans are not big enough you need the biggest CFM 16" cooling fans you can get.

I have 1 16" on my 96 F350 and it does ok unless it's extremely hot and not moving much.
 
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Might seem silly, but is the fan installed on the clutch such that it’s rotating in the correct direction?
The reason I bring this up is you mentioned air pushing out of the fan shroud gaps which implies the mechanical fan is trying to push air into the radiator, vice pulling air through it.

Another thought might be a bad / plugged / fowled radiator or just an undersized radiator. Was the truck a gasser before the conversion and did you reuse the stock gasser radiator?

Posted edit: I re-read the original post , says "new 7.3 radiator", so that takes fowled radiator off the possibilities list.
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Are you sure you have all the air bled out of the cooling system? Sometimes you have to jack the front of the truck up to get it all out.
 

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Are you sure you have all the air bled out of the cooling system? Sometimes you have to jack the front of the truck up to get it all out.
Assuming the degas bottle is the highest point in the system and the thermostat opened, I can't imagine an air pocket would stay in the engine.

OP, are you running a 7.3 degas bottle in the stock location and if so, how is it connected to the cooling system?
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Discussion Starter · #6 ·
Thanks for the responses.

9297oldram- the 2- 12" cooling fans are in addition to the stock dodge fan clutch which is all new. They were only added to keep the ac cool at idle because the first mechanical fan clutch was not locking up at idle. The new fan clutch is pulling air through the radiator at idle along with the 2 pushers. As for air in the cooling system, When filling the degas bottle I left the plug out on the front of the head right next to the thermostat to let air out while filling, and have ran the engine with the cap removed. I have over 600 miles on it so I think if there was any air left it would have worked out by now?

Antonm- The mechanical fan is definitely pulling air the correct way through the radiator (I don't think the fan can be mounted backwards on the clutch if I am remembering correctly as the fan is offset to mounting surface). If I put my hand or a piece of paper in front of the intercooler I can feel it sucking and it is blowing a bunch of air towards the engine. It almost seems like the air blowing out the side of the shroud is due to the air leaving the edge of the blades and hitting the inside of the shroud and being routed out the side instead of out the back. This is only felt significantly on the drivers side. Like I said I can feel a ton of air being blown toward the motor as well as being pulled through the lower radiator. It almost seems like the is to far into the shroud. I know how important shrouds are which is why I am running one, but I have thought about removing it and driving to see if it is somehow causing turbulence, and maybe trimming it some more. Something of note. Even with a fan plugged into the wall and hanging on the front bumper in addition to the 2 electric pushers and mechanical fan the temp creeps up at idle. Yes brand new 7.3 mounted and plumbed exactly as stock. Also when filling the truck was parked uphill with degas for sure at highest point. I also teed into the line from degas bottle to the radiator yesterday and put 13 psi on which held for a few minutes so rad cap seems ok.

When I get a chance here in the next few days I am going to beat on the 7.3 when its hot out and then let it idle and check upper and lower radiator hose temps to get a baseline.

Any ideas on the black smoke out the pipe in drive at idle or if 550-650 egt is too high for being in drive at idle with A/C on?
 

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Do you have the smoke screw ( pre boost ) flush on the inside of the AFC top?

Is the IP just about or all the way to the head to advance the timing?

Are you sure those Ducky's are popped to spec?

If it was mine i'd jack the front of the truck up about 8-10" and leave it like that overnight then pull out the pipe plug at the front of the head to see if anything comes out. I have a radiator drain petcock in that plug so it's easier to check.
 

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Discussion Starter · #8 ·
I backed the smoke screw off 5 turns from how it was sent after rebuild to get egts manageable. I will pull the top off and see if it is flush. IP was locked when I received, installed with #1 at TDC and cam and IP gears lined up to "E". I went to advance the timing an 1/8" about a week and a half ago as I thought maybe it was slightly retarded causing high egts but I was not even able to get an 1/8" bump before it bottomed out on the slotted holes. Maybe got 1/16" which seemed kind of odd as I have see where people can push it all the way to the head. As far as injectors I am not sure but I would assume so as they are brand new injectors with new bosch bodies.

You think it would be worth jacking up and leaving overnight with the degas cap loose? I pulled the plug at the front of the head yesterday to install the new temp sender in that spot and and amazing amount of coolant came gushing out before I could get the sender seated because it is so much lower than the degas/radiator. I
 

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I have DAP 5x12's in my 97 and THD 5x12's in my 92 and they don't smoke and I have a hx35 on both engines.

It's not going to cost you anything to jack the front up and check it at least it would rule out that problem.

I used the 1st Gen Ic and radiator in my 96 F350 with a single 16'" electric fan and no engine fan and very seldom have cooling issues. Unless it's extremely hot out like I said.
 
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Discussion Starter · #10 ·
I will give that a try. Do you know what your EGTs are in drive with ac on in your blazer? I wish I had a way to load up that 7.3 at idle to get the EGTs up to 500-600 so I could see if the cummins is indeed running too hot overloading the cooling system or if it is actually a cooling system issue. That would be a really long burnout though lol.
 
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I don't have AC on either truck. Is the overheating just happening when the AC is on?

I only have a Pyro on my Ford and i've never seen over 1200 degrees and I have my VE pump turned up. The Ford is my hauling and towing truck also.
 

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Discussion Starter · #12 ·
I have not tried with the A/C off yet. Currently adjusting the A/C charge each day trying to get the temps as low as possible, once I get that done I will drive around with it off and see if that makes any difference. This thing will hit 1300 + no problem once the converter locks and that is with the smoke screw backed off 5 turns and the fuel pin turned back to the almost stock position, smoke under acceleration is minimal to none now once the turbo spools. I also tried backing the full power? screw on the back of the pump off some but I got long cranks where I had to give it throttle to start so I moved it back to where it was set and it starts immediately again so I am guessing that is already at the least aggressive position. Also I made a boost leak tester and had pretty good leak at the intake horn that was fixed with a new gasket and some sealant on the intake bolt threads. I should probably boost leak test again but I cant imagine that could cause an overheat at idle.
 

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If it was mine i'd be testing the cooling system with the AC off, that way if you still have overheating problems you'll know it's not because of the AC.

I have my stock fuel pin ground for more fuel, power screw is in about 2 turns, smoke screw flush on the inside and timing advanced. I don't see over 25 psi of boost, have a HVLP set at 8 psi and never drops below 6 psi.

A boost gauge will tell you if your having boost problems.
 

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Discussion Starter · #14 ·
I will leave the A/C off on the way home today and see if it behaves any different in traffic.
 

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I will leave the A/C off on the way home today and see if it behaves any different in traffic.
That's sounds just miserable. I'm not far from you (I'm just north of San Antonio), and I won't drive without AC.

If the AC broke in ever vehicle in my little fleet, I'd rent a car before driving without AC.
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In my Fummins swap truck I used a giant fan off some industrial Cummins I think (part number visible in pics on page 8 of the below linked thread) the stock 12 valve fan is actually kinda small. I have no overheating issues driving around in San Antonio with the AC on in traffic, temps never get above low the 190's.

The only issue I have (more of an annoyance really), is before the engine heats up and the fan clutch kicks in, there isn't enough airflow across the AC condenser to make it work well. So when you first get in the truck and its hot as all heck inside, the AC kinda sucks until either you start driving or the engine get up to temp enough for the fan to actually start pulling air. But once the engine is up to temp , and the fan clutch is working, the AC works fine even at stoplights/ in traffic. I've though about adding some auxiliary electric fans for the AC condenser, so the AC would work good even with the engine cold, but I haven't bothered yet.

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In my Fummins swap truck I used a giant fan off some industrial Cummins I think (part number visible pics on page 8 of the below linked thread) the stock 12 valve fan is actually kinda small. I have no issues overheating issues driving around in San Antonio with the AC on in traffic, temp never get above low 190's.

The only issue I have (more of an annoyance really), is before the engine heats up and the fan clutch kicks in, their isn't enough airflow across the AC condenser to make it work well. So when you first get in the truck and its hot as all heck inside, the AC kinda sucks until either you start driving or the engine get up to temp enough for the fan to actually start pulling air. But once the engine is up to temp , and the fan clutch is working, the AC works fine even at stoplights/ in traffic.

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If he's using the 1st Gen fan it's smaller then a 2nd Gen fan.
 

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Discussion Starter · #18 ·
The fan I have is new and the part number shows it fits 91(intercooled)-2002. It is a 22" 7 blade.

Antonm, It looks like you are still in the process of your swap and your other trucks are sticks? I was curious if you had any input on EGTs at idle in drive as they seem really high to me 550-660? from what I can find on the forums it seems like 450 or so should be normal. LOL I actually don't mind the heat, only trying to get the A/C nice and cold so the girlfriend will be able to ride in/drive this truck.
 

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The fan I have is new and the part number shows it fits 91(intercooled)-2002. It is a 22" 7 blade.

Antonm, It looks like you are still in the process of your swap and your other trucks are sticks? I was curious if you had any input on EGTs at idle in drive as they seem really high to me 550-660? from what I can find on the forums it seems like 450 or so should be normal. LOL I actually don't mind the heat, only trying to get the A/C nice and cold so the girlfriend will be able to ride in/drive this truck.
The 2010 F250 Cummins conversion truck is pretty much done. Its a running and driving truck, only thing left to do really is make the cruise control work (and maybe some cosmetics, but those are still maybe's). Its an automatic (still has the factory 5r110 the truck came with), but I don't recall off the top of my head the idle EGT's.

The 2005 Excursion Cummins conversion really hasn't gotten started good yet. I just got the engine back from the machine shop and I'm in the process of putting it together.

The 97 Dodge is a manual trans truck (the only thing I know about 2nd gen dodge automatics is that I don't want one), but that truck's AC works just fine here in San Antonio too.

The next time I drive the 2010 I'll check the idle EGT's to see what they are in drive with the AC on.

Post edit: Looking through the pictures I have saved on my computer, I found one of the 2010 idling with the AC on, but the trans was in park at the time. I'll make an effort to see what the difference is (if any) with the trans in drive. Although, I'm not sure it'll be apples-to-apples for us as all my Cummins engines are P-pumped. They may behave differently from the VE's , IDK, never played with a VE.

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Discussion Starter · #20 ·
Thats about what my 7.3 runs at with ac on idling. I wonder what seems to be causing the higher idle egts on this 12 valve. Anyway I drove it home with the A/C off yesterday and it ran 190-195 until I got home and let it idle to see if it would creep at a stop and sure enough it slowly kept climbing- rad inlet around 206 and outlet around 180 which would be 190 plus with A/C on. I dont see how the fan could possibly be on wrong and the cup to the blades is facing the right way. I can feel it sucking air through the center of the radiator but blowing air forward at the corners. I was thinking maybe the fan was too far into the shroud and the air was being pushed into the shroud and back forward so I removed the shroud (and accidentally broke it in half in the process...) and the fan feels the exact same. Like it is sucking air through the center and blowing forward at the corners. Made no difference with or without shroud driving around and idling still have temp keep climbing. I looked at the fan on my 7.3 and it sits about halfway in and out of the shroud as opposed to this fan sitting completely inside the shroud (possibly causing it to not create a vacuum effect?) after all of that I noticed what looks like fuel or oil around the #5 injector hold down, it was either bubbling from the hold down or the heat from the head. Probably wont get back to the truck until the weekend now since I am not driving it until I figure out the injector issue. I am going drive the 7.3 to work towing the boat with A/C on shows it should be 103 out and then shoot the upper and lower radiator hoses after driving in traffic and after idling for an extended amount of time to get a baseline of what the inlet and outlets should be.
 
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