[Full Throttle Transport]

Hey guys, kinda stumped here.

I've got a 96 Freightliner FL60 with a 1996 5.9 from a dodge truck in it. I am having overheating problems that nothing seems to fix. When it's loaded, around 20,000 - 24,000 lbs total weight including the load, truck and trailer, it will heat up while I am at highway speeds and climb to about 220-230 and stay there until I stop. It will stay at 220-230 even on level ground, even at temps of 40-50 degrees outside. Once I stop, it cools down pretty quickly and stays about 160-180 when it's not moving. The fuel plate is slid about halfway forward and no other mods have been done. It doesn't smoke under load really at all. It's got 4" straight pipe from the turbo back and splits into two 4" stacks under the cab, so I shouldn't have an exhaust restriction.

In an attempt to fix this problem i've replaced the thermostat twice, put a brand new 5-blade water pump on, replaced the head gasket, verified the temp guage was accurate, and extended the fan shroud to extend past the back of the fan. None of those things did anything to lower the temps. I read about upgrading the water pump to a 6.7 pump, which has 7 blades rather than 5. Last night I did the water pump upgrade to the 6.7 pump and went for a loaded test drive, it runs maybe 5-10 degrees cooler, but it's definately not fixed. It's not losing any coolant and the radiator fins are clean and straight. The intercooler is clean, there's no debris built up between the radiator and intercooler. While I was changing the headgasket, the inside coolant passages all looked great, no rest or scale buildup at all.


The only two things I haven't done, that I can think of, is have the radiator boiled or rodded to make sure it isn't blocked internally and to replace the fan clutch. A fan clutch is big bucks, and it seems to me like it should stay cooler running down the road at 60vmph with 40 degree air being pushed across the radiator anyway.


What are your opinions? Am I missing something?

Thanks in advance

 

[Joe4d]

not enough coolant. thats why it cools off sitting still. If you had plenty of coolant it wouldnt heat up moving. Now the WHY is the issue.
suction hose wrong ? collapsing when the pump gets moving ?
clogs in radiator ? before yanking it and getting it rodded Id get a heat laser gun see if you notice any hot or cold spots in the radiator.
you have an exhaust temp gauge ? maybe something is up there and egts are going through the roof under load, but is fine at idle.

 

[LNaugle]

I agree with temp gun deal.... Also, what kind of fan clutch did they use in the 60? I assume its not air so?

 

[Philip]

At the temps you say it is running. Your fan should be on all the time. So most likley you have a problem there.

I would pull the raditor and get it cleaned also.

 

[Joe4d]

im liking the collapsed suction hose, does it still have the steel spring insert ?

 

[Full Throttle Transport]

Thanks for the quick replies guys!

My 60 came with a viscous fan clutch.... I guess some also came with air and electric clutches too according to Freightliner. Anyway, I don't really "hear" the fan working when I am driving, but with straight pipes and lots of wind noise I can't really say for sure that it's not working either. I can say that when it's idling, I can take my hat off and lay it on the front of the intercooler and the draw of the fan will hold my hat there, for whatever that back yard test is worth lol.

The suction hose is ok. It was new when I put the engine in and is rubber in 2 sections, each about 6 inches long, with a steel pipe in between them. It doesn't have any sharp bends or possible kink spots. I don't recall if it had a spring in it or not. The whole system holds about 6 gallons of coolant all together.

Clogs in the radiator is definitely possible. From what I can see, through the inlet and outlet, it looks good. I can see the ends of probably 4-5 tubes and they all look clean. Of course that's not to say that the others I can't see are good or that they aren't plugged in the middle somewhere.

I don't have an EGT gauge yet, but I am assuming I am ok there. I hate to assume, just so we're clear there lol. It's not "turned up", has the stock injectors in it, stock turbo, and doesn't smoke even on a long hill. The truck will stay at 220-230 even on long flat stretches when it's not even pulling hard, so EGT's should definitely not be a problem at that point. But again, I agree that I don't know that for certain because I don't have a gauge.

I will take it out again tonight and try the infrared gun to see what that tells me.

 

[macko300exc]

Have you checked the radiator cap? Are you losing coolant? Is the cooling system building pressure beyound the pressure rating of the cap?

 

[Full Throttle Transport]

Have you checked the radiator cap? Are you losing coolant? Is the cooling system building pressure beyound the pressure rating of the cap?

The cap is good. I am not losing any coolant at all.

 

[Full Throttle Transport]

im liking the collapsed suction hose, does it still have the steel spring insert ?

I checked the lower hose a little while ago, it does have the spring inside.

 

[Full Throttle Transport]

I went out again tonight and again it got up to about 220 and stayed there during normal 65 mph runs across flat ground with the gooseneck trailer and a 5500 lb dually on the trailer. On uphill climbs it would venture toward 230 and the cool back to 220 after the cresting the hill.

I pulled over on an off ramp while the gauge was showing 210-220 and used the infrared gun. Thermostat housing showed about 200-205, top of the radiator at the hose connection showed about 197, the radiator was uniform in temp across the fins, the water inlet to the block showed about 170. After just enough time to check those areas and close the hood, the temp on the gauge was back down to about 195-200.

I am starting to think the problem is the fan clutch. Maybe engaging enough to cool it down quick with no load on the engine, like when idling. But not engaging enough to cool while the engine is under load, even if it's a fairly light load cruising across flat ground at 65.

The only question I have about that theory is this.... With it being 52 degrees here right now, shouldn't there be enough air blowing through the radiator at 65 mph to keep it cooler than 220, even with the fan clutch not working real well?

What are your thoughts?

 

[macko300exc]

How about a bad gauge or sending unit

 

[Full Throttle Transport]

How about a bad gauge or sending unit

I've tried two brand new gauges from O'reilly's. I had an electric gauge first and now a mechanical. I just bought the mechanical yesterday and put it in before the test drive last night.

 

[LNaugle]

Cummins thermostat right? I had a similar issue with an "over the counter" Tstat a customer installed himself.

 

[Full Throttle Transport]

Cummins thermostat right? I had a similar issue with an "over the counter" Tstat a customer installed himself.

Two of the thermostats I had were from O'reilly's, both brand new. They were the normal looking dodge thermostat with a 1" hole for the coolant to come through. The thermostat I have in it now, not sure where it came from or what brand it is, is an industrial or heavy duty looking type with a 1 1/2" hole for the coolant to come through. I wish I would have taken a picture of it before I put it in, but I didn't.

My thinking was that the 1 1/2" hole would let more hot water through to the radiator, thus helping to keep it cooler.


All three thermostats have acted exactly the same as far as temps, how fast it heats up and how fast it cools down.

 

[Full Throttle Transport]

Does anyone know how much air, CFM wise, a factory fan moves?

I am looking at electric fans right now, I have plenty of room to mount them on my big radiator. I have found 16" S-blade fans that are said to flow 3,000 CFM.


The viscous fan clutch is $647 from the dealer and $395 everywhere else that I can find it.

 

[LNaugle]

Electric fans will restrict air flow except at lower speeds. The cummins tstat starts opening earlier than most aftermarkets allowing it to maintain the lower temperature. Also, if the fan clutch is working properly it should be loud when you are hitting those temps, otherwise it is slipping. I would look into both a lil more.

 

[Full Throttle Transport]

Electric fans will restrict air flow except at lower speeds. The cummins tstat starts opening earlier than most aftermarkets allowing it to maintain the lower temperature. Also, if the fan clutch is working properly it should be loud when you are hitting those temps, otherwise it is slipping. I would look into both a lil more.

I am leaning more and more toward the fan clutch at this point. I don't hear the fan, even when the temps are 220 or above. Once you shut the engine off, the fan will continue to spin for a good 5-10 seconds before it finally slows to a stop. It doesn't show any signs of leakage, but it's definately older and possibly the original clutch.

 

[LNaugle]

That suckers BAD! Get a good one.... If aftermarket make sure is Hayden hd.

 

[#40Fan]

I'd get the radiator cleaned/replaced.

 

[Full Throttle Transport]

Just ordered two electric fans, a 16" S-blade and a 12" S-blade. They're supposed to be here by 4:30 tomorrow. I will post an update after the install and test drive.