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99 Freightliner problems

fortwayne

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Ok I am doing one of those hit and miss repairs.

The water temp in my truck has been running around 220-260 pretty hot, eh.
The first step was drain the radiator, all new fluids and then a new thermostat.

However, after checking for any leaks after the repairs, nothing was found and it idled all night just fine around the 180-200 range with the rpm's running at around 800-900.

However, while running down the road the temp quickly goes back up to 220-250'ish or so.........then clicks back down to 200.........

So what gives?
Is it possible I just have a sensor that is goofy and old?

Can't if think that a water pump could cause this issue....
 

Dakota

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I was told by tech's that the older freightliner ran hotter, don"t know if that is true or not. When driving and the temp rises do you here the fan clutch come on, it's pretty loud and hard to miss when it is on. Also 220, 230 is normal at least for the older frieghtliners. I'm sure Greg will know better than me since he has an FL70
 

fortwayne

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that gives me some hope, and sure hope to get more input as well........Greg where are you?
as far as the fan clutch i will pay attention as it doesn't help i don't hear noises all that well...........good enough to pass the physical but engine noises and the like is tough for an old gator like me...........
 

CORLEY5

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Sounds to me like the fan clutch is going bad or the radiator is not flowing the way it needs to.
 

davekc

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Some of the engines on those do run hotter. If it has the original radiator, I would take a lazer temp gun and run it on the length of the radiator and see if you locate a cool spot.
You are looking for a plugged radiator is the purpose in doing this. I am also assuming it was pressure tested when the fluid was changed?
 

Dakota

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When the fan clutch engages on those older freightliners it sounds like someone turned a huge fan on high and it can be quite noisey, this is probably when you notice the temp dropping while driving. I did notice on the older freights I drove that the temp seemed to fluctuate alot, never bugged me though because, the numerous straight six Jeeps I have owned seem to fluctuate alot so I was used the temp guage moving alot. Not to say this is normal, but it might be normal for the Freightliners:)
 
R

riverrat

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a quick and easy way to chech to see if the radiator is plugged it to run it until the temp is where ig is hot and then stop shut the engine down and spray some water on it, where the water quickly evaporates is where the coolant is flowing, the places that the water doesn't evaporate is where the stoppage is, and if it were me I would be looking closely for a plugged radiator from what you described.
 

Deville

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Mine runs about 210-220, never had a porblem even during the hottest of days.
On a cold startup the fan should be spinning, on a cold day when the truck has to go though it's warm up sequence you should hear the fan wind up with the motor & than it will turn itself off after about 30 seconds.

Don't forget there are two thermo-stats on the Cat motors, Cat recomends they be replaced every few years.
 

greg334

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I'm assuming you have an FL70?

I don't really experience the "running warm" issue with mine - however lately on long idles it heats up and I have to replace both stats.

Under a heavy load going up a steep grade I would see 240 but then the fan kicks on (which you can't miss) and the temps drop a lot. If you are running empty, then it is a cooling problem, not a fan problem.

There are two stats on some of the ISC models and I understand the 3126 also has two on some models, but first I would check the temps on the radiator as Dave described. I would be concerned with the temps coming out of the engine too, at the metal tubes because if they are high, say 200 or so, then it is in the engine. Otherwise it could be a radiator problem or no problem at all but a sensor going bad which for the ISC is $8.

A good flush is needed with both the 3126 and the ISC engines (actually all engines should get a flush on a regular basis) which is not something many can do at home because of the chemicals used. I hessitate to get it done at a dealer because of the cost but it gets rid of the crap in the engine. Radiators are cheap, relativity speaking - I have found them under $400 - so it may be an easy fix.
 

fortwayne

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thanks everyone - i am going to follow these tips and tricks, but if you have any other points let me know here on drip me a pm. once again thanks. and no i don't think the petro pressure tested it after they drained it..........that is why i am starting to think that i have a plug up somewhere in the radiator or maybe it is just running normal etc etc.......
 

nightcreacher

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you didnt mention brand of motor.250 degrees in a cat,you already blew it up
sounds to me your temp guage may be bad.your clutch fan should come on around 220 degrees,then shut down about 190.an electronic engine,if y our running as hat as you say,will pop a code
 

Deville

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I'm assuming you have an FL70?

I don't really experience the "running warm" issue with mine - however lately on long idles it heats up and I have to replace both stats.

Under a heavy load going up a steep grade I would see 240 but then the fan kicks on (which you can't miss) and the temps drop a lot. If you are running empty, then it is a cooling problem, not a fan problem.

There are two stats on some of the ISC models and I understand the 3126 also has two on some models, but first I would check the temps on the radiator as Dave described. I would be concerned with the temps coming out of the engine too, at the metal tubes because if they are high, say 200 or so, then it is in the engine. Otherwise it could be a radiator problem or no problem at all but a sensor going bad which for the ISC is $8.

A good flush is needed with both the 3126 and the ISC engines (actually all engines should get a flush on a regular basis) which is not something many can do at home because of the chemicals used. I hessitate to get it done at a dealer because of the cost but it gets rid of the crap in the engine. Radiators are cheap, relativity speaking - I have found them under $400 - so it may be an easy fix.

I've never been a fan of flushing a cooling system. Change the coolant every 2 years, run some wayer though the system, drain & refill with 50/50 & some coolant additive. I've heard too may horror stories about the dangers of flushing a system that has high miles on it.
 

Deville

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you didnt mention brand of motor.250 degrees in a cat,you already blew it up
sounds to me your temp guage may be bad.your clutch fan should come on around 220 degrees,then shut down about 190.an electronic engine,if y our running as hat as you say,will pop a code
250* is the red zone for those motors, u would get a shut down message or the engine protect light would come on.
 

Dakota

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250* is the red zone for those motors, u would get a shut down message or the engine protect light would come on.
Yeah, I was gonna say most of these truck will shut you down before it gets hot enough to do damage, at least the ones I have driven
 

fortwayne

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it seems like it was the thermostats as its been ok for a few days....however, i never really have heard the clutch fan kick in.........i either need hearing aids or maybe the thing actually doesn't have a clutch fan.....or its shot to heck.........man i am glad i ain't a mechanic....but it seems ok for now
 

stamp11127

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Would you rather have expensive problems down the road or take care of a potential problem now? I would have a second opinion on the operation of the clutch fan before the summer gets here. Better to change it at your convenience instead of on the road and under load.
 

Dakota

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it seems like it was the thermostats as its been ok for a few days....however, i never really have heard the clutch fan kick in.........i either need hearing aids or maybe the thing actually doesn't have a clutch fan.....or its shot to heck.........man i am glad i ain't a mechanic....but it seems ok for now
If you can hear the radio and use a cell phone you'd certainly beable to hear the fan kick in, sounds like a jet is under your hood LOL
 

guido4475

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An air-powered fan clutch is alot louder than a viscous drive fan clutch.I like an air-powered fan clutch myself.
 

Deville

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Like I said earlier when u start the truck the fan is running, if it's really cold out & the truck goes though its automated warmup procedue which is the engine reving at 1100 rpms from any where to a few seconds to 10 mins, you will hear the fan, it will run for about a minute and shut off. You can't miss it it sounds like a huge fan running.

Next time you start the truck cold, open the hood and see what;s going on. if the clutch fan isn't working the fan won't spin properly.
 
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