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99 5.9 overheating while towing

57K views 37 replies 25 participants last post by  Dodge2002skull 
#1 ·
I have a new issue. While towing my 34' fifthwheel up 7% grade, my temp shot up to max. I changed the clutch fan cause it wasn't kicking in like it use to. That helped but still running out of the operating range. Turning down chip didn't help. Drained my radiator down to check if was clogged up but it looks great. Had some stuff in fins but washed them out. Thermostat maybe? Any input would be helpful. Never ran hot before.:CRY:
 
#3 ·
:agree2: and maybe your thermostat...does it want to run hot if you to get out there without the trailer...slight possiblilty of your waterpump (just putting it out there)
 
#4 ·
have you relocated your breather bottle or is it still in the factory location. That will cause the radiator to be coated in oil grime
 
#5 ·
:thud: that's why you emty it out every oil change...duh :lol3:

well at least i do...:T:
 
#6 ·
the thermostat is most likely the cause. i have done about 5 on 24v cummins trucks. on the first one i cut the thermostat housing to remove the center and it fixed it and then i got a good one from dodge.
 
#7 ·
i was thinking about just replacing mine now, before i ever have an issue...figure 165k on the factory one..wouldn't hurt...
 
#8 ·
I'd bet its the oil from the breather tube blowing all over your radiator. Our year trucks dont have the bottle. At least mine didnt come with one, but they still get oil all over the bottom of the radiator and then you have a big dirty oily mess. I suggest cleaning the radiator and extending the breather tube.
 
#9 ·
ok I checked the amount of coolant flowing when cold (hardly noticed) to when it was warmed up (ok it moves pretty good) I'm thinking T-stat is working. Cheap insurance to change it though. I did take a bottle of dish soap and water mix and spray on warm radiator to cut the grease. Not much on there. Then I took a piece of 3/8 copper tubing with the end flattened around a small nail (pulled nail out to make small orifice) and hooked it to air compressor. Man the stuff that blew out of the fins. I keep my truck clean. Very clean. I was shocked. I hope that fixes it but I'll keep you posted. Thanks for the tips.
 
#10 ·
plugged radiator


You have to pull to radiator out it only take a few minutes, I had the same problem a year ago after chasing race cars down in Baja (can you say silt combined with oil from breather) I used a wide nozzle on my pressure washer and was blown away at how much mud came out.
 
#11 ·
I am having the same problem with my 99 CTD. The problem started last year while pulling my 26ft toy hauler up a grade in the summer time. Tranny temp light came on as well as the engine light, temp shot up to 240. I was running the heater on full blast and having the pull over every couple of miles for 20-30 mins at a time to let it cool a bit. I had the radiator flushed and pressure washed, fan clutch and thermostat checked. It still does heats up if I'm climbing into the mountains. Flat ground ok, up hill bad. My trailer is less than 10,000 lbs loaded. I shouldn't be having these problems, but sure enough everything was repeated this last friday afternoon. If you find out what the problem was/is please let me know. And if anyone out there has any suggestions I like to hear them.
 
#12 ·
I am having the same problem with my '01 Dodge, almost word for word as Bankrz.... I have replaced the thermostat, the fan clutch, sent the radiator to the shop for a flush and clean, had the tranny (auto) serviced and adjusted, replaced the serpentine belt. No heat problems on level hwy...but pull a steep grade with a load and watch out ! help someone please! By the way this truck is all stock...and I drive like the grandpa I am.
 
#13 ·
Just a suggestion, when I rebuilt my trans last year I added a Mag-Hytec double deep pan and changed over to Ams-oil synthetic trans fluid. If I'm lucky my trans temp gets to the 150 mark and no matter how hot it is outside or how hard I run my truck the coolant temp gets no higher than 190. Just my .02 worth.
 
#14 ·
As the thermostat opens up at 190, it will allow the engine temps to climb a bit. This is normal up to a point. Checking the t-stat is simple. put it in a pot of water with a thermometer and bring it up to 190. It should open FULLY just past 190. If not, it may have leaked some of the wax from the pellet, and must be replaced. Brass pellet t-stats used to be available, but I haven't seen them in a while. Couldn't find one for mine. My t-stat failed OPEN. Didn't know that was even possible. Bought it that way, maybe it was fooled with.

Dropping it a gear will help quite a bit too. Causes a leaner fuel mix, which in a diesel, runs cooler. Works for me, but I only tow 5k usually.
 
#15 ·
If you have an auto trans...do everthing you can to dissipate heat. Get a Aux trans cooler (Not the one with a visible tube and fins. ) I think it was called a Mesa cooler? The pan is is a nice touch but for the average trailer towing it's not needed if the cooler is properly sized. long time since I've had an auto trans but heat killes them. If the tranny is hot it heats up the coolant if they are still contected.
 
#16 ·
My 2 cents - - -

Have towed a bit in my life but new to towing with my wife's 1999 Dodge 4X4 2500 auto trans with no modifications and 105k miles. Pulling a 25ft Airstream (weight ~8700 lbs). First time the tuck has pulled any thing relatively heavy (has pulled may horse trailers previous with mild overheating). Had it overheat on a long pull in 3rd gear pulling at about 1500 rpm. Pegged the engine temp gauge and the light for the transmission came on. After I pulled off and stopped and placed in park and ran the engine at about 2000 rpm for 3-5 mins temp came down. Started up again and after hill trans would not go into overdrive (temp lockout). When it cooled down more the trans appeared to work fine.

Stopped at car wash and cleaned out the radiator. Still got hot after that.

My thought is that on pulls it is the trans temp that is heating up the engine. I think this because I look closely at the cooling system and in my mind it is kind of a stupid design. I will explain. The trans fluid is pumped from the trans to a heat exchanger (trans fluid circulating through a unit with engine coolant in it on the passenger side of the engine). Then the trans fluid goes up to the aux trans cooler and then back to the trans. The part that appears stupid to me is that the heat exchanger take engine coolant directly from the engine block (so it is taking HOT engine coolant) and then circulating it with HOT trans fluid and then dumping the engine coolant directly back into the HOT engine making the engine even HOTTER.:RANTIN:

My fix - another auxiliary trans cooler just behind the trans on the driver side. B&M Cooler with an temp activated integrated fan. Now the trans fluid runs from the trans to the new cooler then to the heat exchanger and then to the auxiliary trans cooler in the front of the radiator then back to the trans.

Have done moderate/heavy pulling for 20 mins straight since then and and engine temp maxs at just over 190.

We will see . . .:w:
 
#26 · (Edited)
Have towed a bit in my life but new to towing with my wife's 1999 Dodge 4X4 2500 auto trans with no modifications and 105k miles. Pulling a 25ft Airstream (weight ~8700 lbs). First time the tuck has pulled any thing relatively heavy (has pulled may horse trailers previous with mild overheating). Had it overheat on a long pull in 3rd gear pulling at about 1500 rpm. Pegged the engine temp gauge and the light for the transmission came on. After I pulled off and stopped and placed in park and ran the engine at about 2000 rpm for 3-5 mins temp came down. Started up again and after hill trans would not go into overdrive (temp lockout). When it cooled down more the trans appeared to work fine.

NEVER PARK!!!!!!!!!!! NETURAL ONLY!!!!!!! You will fry that tranny that way

Stopped at car wash and cleaned out the radiator. Still got hot after that.

My thought is that on pulls it is the trans temp that is heating up the engine. I think this because I look closely at the cooling system and in my mind it is kind of a stupid design. I will explain. The trans fluid is pumped from the trans to a heat exchanger (trans fluid circulating through a unit with engine coolant in it on the passenger side of the engine). Then the trans fluid goes up to the aux trans cooler and then back to the trans. The part that appears stupid to me is that the heat exchanger take engine coolant directly from the engine block (so it is taking HOT engine coolant) and then circulating it with HOT trans fluid and then dumping the engine coolant directly back into the HOT engine making the engine even HOTTER.:RANTIN:

Close, the fluid goes to a oil heater, and then to the radiator then back to the transmission.

My fix - another auxiliary trans cooler just behind the trans on the driver side. B&M Cooler with an temp activated integrated fan. Now the trans fluid runs from the trans to the new cooler then to the heat exchanger and then to the auxiliary trans cooler in the front of the radiator then back to the trans.

Have done moderate/heavy pulling for 20 mins straight since then and and engine temp maxs at just over 190.

We will see . . .:w:
Answers in blue hopes it help.


As the thermostat opens up at 190, it will allow the engine temps to climb a bit. This is normal up to a point. Checking the t-stat is simple. put it in a pot of water with a thermometer and bring it up to 190. It should open FULLY just past 190. If not, it may have leaked some of the wax from the pellet, and must be replaced. Brass pellet t-stats used to be available, but I haven't seen them in a while. Couldn't find one for mine. My t-stat failed OPEN. Didn't know that was even possible. Bought it that way, maybe it was fooled with.

Dropping it a gear will help quite a bit too. Causes a leaner fuel mix, which in a diesel, runs cooler. Works for me, but I only tow 5k usually.

Cummins T-Stat's fail OPEN

First, remove your radiator and inter cooler and then hit them with a power washer and clean them out, second check water pump, T-stat, and cut out the muffler on your exhaust train, what are your pyro's up to?

Its usually simple things that balloon to this.
 
#18 ·
Update on engine temp. Drove 4000k miles in 10 days. 7% grades towing my 10k lb 5th wheel. Normal temps all the way. I believe blowing the radiator out was the trick. I removed approx 1" deep in the bottom of a 5 gal bucket of debris from the radiator fins (after I had hosed it out). I used a piece of 3/8" soft copper pipe (end peeded down around a small finish nail, remove nail) hooked to my air compressor. Careful not to bend the fins! Blew it out from back to front.
 
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#21 ·
It's a "Pro Tech" rack. I like it cause the rear section I hardly use and makes it easy to have a rack and still tow the 5th wheel. They have all kinds of options.
 
#22 · (Edited)
LAY OFF THE A/C. and if its hot out you could crank heater and roll down the windows. it helps its like having a second radiator.
Keep the radiator clean from debris, if you need to flush the cooling system , might as well take it out and clean it too.
Drop a multimeter probe in the radiator and check for voltage, it should be close to zero, if not its time to change it.
Relocate that crank case breather tube mopar1973man's site has a nice overview on what to do with that thing.
Bugs love to fly over the road and get wedged in your radiator, easy fix to cut down on that is a screen mesh zip tied to the inside of the grill in my case its wired 6 inches in front of the radiator(previous owner).

oh and speaking of belts, check that your AC still works correctly, mine siezed which later caused the AC clutch to seize, eventually the belt started smoking, afterwards it finally started to squeal. never knew there was a problem until then.
 
#23 ·
i just flushed my radiator out 2 days ago....i was wayyyyy overdue for that....but the dang thing runs a lil bit cooler now pull'n a load of wood up some hills....
 
#24 ·
There is also the possibility of just pulling to hard. Perhaps slow down or downshift.
I found that air actually is pulled through the radiator and forced forward back through the radiator. Fabricated some shields to block on sides and inatall a pipe insulator across top to block reverse flow. Haven't tryed yet on heavy pull. Will report.
 
#25 ·
lol

Don't pull so hard? You must of had a Ford in your lifetime. lol just kidding. I go by what I have always done. If it acts different than it use to then something changed. I haven't had any cooling problems since I blew out the radiator with the pipe BTW. Even on the hardest pulls (7% grade or more) it never gets more than a sliver above half (A/C blastin on 100 degree days)
 
#27 ·
On a recent trip up to a mountaintop on a dirt road in 4X4, I found the truck ran a lot cooler in 4x4 Low. I need to pull the thermostat and replace it ant the serpentine. Maybe a good job for this weekend!
 
#28 ·
a few years back i was pulling a loaded trailer up the pass in lower Oregon going to sacramento for a race .near the top i hit very high temps.finished the trip coming back drove over that pass at 1 in the morning to avoid the very high temps outside.it did help.when i got home i changed my thermostat and it didn't help at all.i then relocated my breather tube,removed the radiator and hosed it down with a good degreaser.let it soak for about 2 hours the hosed it off.i have never had a over heating problem again.a good way to check to see if your radiator might be full of crap is to rub your hand on the inside of your fan shroud..if its full of crap it usually means it has pushed a ton of crap into the back of your radiator.
 
#29 ·
I have an 01 2500 with a 5 speed manual transmission 4" MBRP exhaust K&N Air intake. I have don all of the above. New stat ,belt ,cooling system flushed ,rad cleaned.The main difference with mine is that it overheats in ther summer and will not provide proper heat in the winter even though the temperature gauge reads a good temp. Could it possibly be the water pump.
 
#30 ·
how many miles do you have through your engine, it could be the water pump it seems like there is not enough flow through the block /radiator, and assemblies.
 
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#32 ·
Overflow bottle

I know this thread is old but people still come in here to educate themselves.

I had the over heating problem for years. I finally took it too my buddy mechanic and he found out that the breather bottle was knocked loose and the breather tube was just emptying out into my fans, radiator, tranny, ect.
He EXTENDED the tube and took the bottle off and threw it away. Then he had to spend hours cleaning all the fins with degreaser.
We could not see down far enough to know it was a problem with out tearing it apart. Now it never over heats.
 
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