How hot is HOT!?

[WCantrell]

Assuming that all the cooling components are working correctly:



1. At what coolant temp should the fan clutch lock-up?

2. What is the best operating temp for the engine? Does it like it better down around 180?

3. What is the maximum coolant temp that I want to tolerate for long distances? 215?

4. What is the maximum coolant temp for short time periods (2 min or less)?



Here's the background: Phoenix in the summer... I haul a 3 horse slant, and am having uncomfortable moments watching the temp guages on grades. My factory temp was bouncing around, so I recently installed the autometer gauge. I have the updated factory fan and clutch (new). New water pump. The radiator has been pressure washed, and the thermostat has been replaced. Before I start replacing stuff that may not be broken, can you guy help me out with a good baseline?



Thanks!

 

[cerberusiam]

A little info on the truck might help tell what you should expect. Auto manual, gear ratio, tire size, etc. Got to the Discussion Forums drop down at the top of the page, choose User control Panel, then Edit Signature from the left panel.



If its an auto its pretty easy to push it up around 220-230 in hot weather on steep grades. Not so easy if its a manual.



Your biggest problem with extended heat is it will eventually get the head gasket and start leaking. Otherwise, 210-220 max for quite a while is not going to hurt it.



The engine will actually be more efficient at higher air temps and coolant temps. The 160 thermostat is pretty cold for a diesel anyway. Racers run these mtors at 300 degrees to suck all the possible HP out of them but its only short bursts. As long as your cooling system and rad cap is good they will run at 240 and not hurt a thing.

 

[JLEONARD]

240 is too hot. Some engine oils will start to break down at that temp.

When boats (Cummins powered)run that hot they can score piston walls.



I say 215 is the absolute hottest I would want to knowingly run for any extended period. Yes if it overheats to 240 or more and you idle down to let the temp drop you won't damage anything... but not a steady diet. Not on my watch.



That said I have run my Jetta diesel up to 240/250 once when the water pump blew before I knew what happened. The oil was defiantely burnt although not too bad according to the analysis I had done when I got it to a shop.

I consider myself lucky that there was no damage.

 

[WCantrell]

Thanks for the input. My sig should show now, sorry newbie at work.

 

[cerberusiam]

240 is too hot. Some engine oils will start to break down at that temp.

When boats (Cummins powered)run that hot they can score piston walls.

Respectfully disagree there, coolant temps at 240 do not break the oil down. Oil temps that high for an extended time will cause issues but cooolant and oil temps do not always correlate.



Remember the oil is cooled by coolant right out of the radiator at its coolest point and coolant temp is read at the back of the block at the hottest point. There could be 40 plus degrees difference between the 2 locations.

 

[WCantrell]

A little info on the truck might help tell what you should expect. Auto manual, gear ratio, tire size, etc. Got to the Discussion Forums drop down at the top of the page, choose User control Panel, then Edit Signature from the left panel.



If its an auto its pretty easy to push it up around 220-230 in hot weather on steep grades. Not so easy if its a manual.



... .

My sig is updated.



Is heat soak an issue for me with an ic truck? One of the things that I noticed on my last pull from NM during the heat of the day, was when I pulled into fuel, the truck idled really low, the dash gauge temp was on the high side of normal (did not have the extra guage yet). When I pulled out, all was fine.



Any ideas?

 

[JLEONARD]

cooolant and oil temps do not always correlate

Exactly. However, they might correllate. I won't take that risk. It's too great.

There could be 40 plus degrees difference between the 2 locations

Yes, again it's possible but unless you know for certainty, it's a major risk.



Many have been burned on this (no pun intended), so again I don't think it's a risk many of us would take.

Hence the much safer route of keeping temps below 215 is better advice.



But once again this is why we are all here... to discuss issues and relate experiences.

 

[cerberusiam]

My sig is updated.



Is heat soak an issue for me with an ic truck? One of the things that I noticed on my last pull from NM during the heat of the day, was when I pulled into fuel, the truck idled really low, the dash gauge temp was on the high side of normal (did not have the extra guage yet). When I pulled out, all was fine.



Any ideas?

Probably, but thats probably normal with a turned up truck. How does your real gauge correlate to the dash gauge?

 

[cerberusiam]

But once again this is why we are all here... to discuss issues and relate experiences.

Yep, I don't disagree with your ideas. I have seen higher temps for longer periods with no issues and considering what I see some of the racers doing it just reaffirms there is a fair amount of wiggle room in the temps.



Be interesting to see what oil temps vs coolant temps vs location does in normal and towing operations.

 

[JLEONARD]

I know in boating, which is similar to towing (but possibly a greater duty cycle), running with high temps definately causes problems.

Usually but not always, the high coolant temps are due to "creep" and are a result of overloading which drives up EGT. High EGT can be tolerated for short bursts, but not the long haul. I don't know what the time is exactly. I don't think any of us do. But once that time is exceeded, piston walls score, rings partially sieze. This is a relatively common occurance in a diesel that is pushed beyond it's limits. This is well documented in "boatdiesel.com" (and would be good late night browsing for those interested).

I have been following a recent thread there where a guy fried a 6BTA when his tensioner failed. He shut down when the buzzer went off (which is set for 210 F) but the engine had already toasted 2 holes.

Since none of us really know where that line is, and it is different for every truck and situation, we should err on the conservative side.



The "knock" on the 6B is that they need to breathe and be cool. Other than that they rock.

 

[MAllen1]

I beg to differ on coolant and oil temp. I drive a tractor trailer with both coolant and oil temp guages. I've noticed that while pulling the oil will be between 20 and 50 degrees hotter depending on conditions. Either way the thermostat should be completely open at 210 regardless. The truck should sustain between 220-240 at short bursts pulling long grades. A high quality convetional oil can handle between 250-300 degrees for short bursts, but not for extended periods. If everything is up to par on the cooling system and you keep getting high on the coolant temp. , I would look at running a semi or full synthetic because of the higher abuses these oils can handle.

 

[WCantrell]

Probably, but thats probably normal with a turned up truck. How does your real gauge correlate to the dash gauge?

I havn't towed with the real gauge yet, as I wanted to get the board's oppinion before I did. I plan to do so after work in the next couple of days. In normal daily driving, the real guage measures 190-200, while the dash gauge stays midway between the 2nd and 3rd hash marks (center of the gauge sweep).



I'll let you know how it fares under a load.

 

[cerberusiam]

I beg to differ on coolant and oil temp. I drive a tractor trailer with both coolant and oil temp guages. I've noticed that while pulling the oil will be between 20 and 50 degrees hotter depending on conditions.

I don't doubt that but there is somewhat of a scale difference between an OTR rig and our light duty trucks. There is a huge difference in the amount of heta generated moving 80k as opposed to 15k. In addition, these trucks have a slightly undersized cooling system compared to big rig.



The rigs I have had experience always seemed to run the same no matter the temps and loads whereas its really easy on a 1st gen with a non-lockup TC to drive coolant temps with the transmission, like upwards of 250 degrees if pulling heavy on a long grade.



The location measured makes a large difference also. Measured in the pan before cooling so you can see your max temps is driven much more by EGT's than coolant temp.



On a big rig, what is the max oil temp you start getting concerned about it? For how long can you run how high a temp before you really should change it? Not looking for exacts just a ball park figure.

 

[Wooter]

We pull a 32 ft 5thwheel - Going east out of Las Cruces, NM on hwy 70, over the Organ Pipe Mtns, Mine will hit 230 before we get to top everytime. Usually have to pull the last 1/2 mile in low gear - I always pull over & let it cool down and then over the top. "Maby 21,000 + lbs gross is a little heavy"

 

[PToombs]

To get back to WC's problem... ... .



WC, your sig says the transmission was done, did you put in an upgraded torque converter? If it was replaced with a stock one, the converter slip will heat the oil, which in turn will over heat the coolant thru the heat exchanger under the exhaust manifold. The best trans mod for these trucks is an updated converter. And a valve body, but for what you do that's not as important.

If you have a stock converter, the next best thing is to add an auxilary cooler.

 

[WCantrell]

To get back to WC's problem... ... .



WC, your sig says the transmission was done, did you put in an upgraded torque converter? If it was replaced with a stock one, the converter slip will heat the oil, which in turn will over heat the coolant thru the heat exchanger under the exhaust manifold. The best trans mod for these trucks is an updated converter. And a valve body, but for what you do that's not as important.

If you have a stock converter, the next best thing is to add an auxilary cooler.

I bought my truck with the fresh transmission (10k miles). It has an upgraded converter(low stall ?)/shift kit/big honkin transmission pan/aftermarket cooler I'm not sure about the valve body, but the transmission was built by a local diesel shop. The transmission temp (teed off the od temp sensor) has never surpassed 190/195. Around town this time of year the guage claims 150.

 

[PToombs]

Ok, sounds like the trans is good and not heat sinking the engine. If it stays under 195, you have a good working setup.

The only other thing I can think of is the radiator getting plugged inside. Is the thermostat a Cummins replacement? Or a NAPA or auto parts one?

 

[WCantrell]

Ok, sounds like the trans is good and not heat sinking the engine. If it stays under 195, you have a good working setup.

The only other thing I can think of is the radiator getting plugged inside. Is the thermostat a Cummins replacement? Or a NAPA or auto parts one?

It has a new NAPA tstat. The radiator has been replaced, did not appear to be clogged on the inside (yea I know you can't really tell). I am planning on replacing the stat with the proper cummins one. When I do that, I'll take the radiator all the way out and see if there is more grime on the ac/ic/rad that can be cleaned off.



Related question:

If I have bumped the timing to much, that can cause overheating. When should that be most evident? All the time, or under load? It seems to build more heat in 3rd than overdrive with speed being equal in both cases.



Thanks again!

 

[cerberusiam]

Related question:

If I have bumped the timing to much, that can cause overheating. When should that be most evident? All the time, or under load? It seems to build more heat in 3rd than overdrive with speed being equal in both cases.

Well, higher temps than with retarded timing but it should not cause over heating unless there is a problem with the radiator. More burn time in the cylinder equates to more heat transfered to the coolant but on the order of 5% or so. The danger of too much timing under load is the heat soak in the cylinder causingit to scuff the pistons and cylinder.



You should see more heat in drive than OD, more rpm's equal more fuel and more heat to dissipate.



The temps you have posted so far sound pretty normal. With a 518 the engine is always a heat sink no matter how many coolers and deep pan you put in unless you completely remove the fluid-to-fluid cooler.



Under a load and in hot weather my 92 has always run in the upper end of the gauge, like 1/2 way to the 3rd mark which translates to around 220degrees IIRC from the gauge I tested it with. With 300k it doesn't seem to be an issue. Sometimes its a driving experience to keep EGT's, engine temp, and trans temp in check.

 

[WCantrell]

Well, higher temps than with retarded timing but it should not cause over heating unless there is a problem with the radiator. More burn time in the cylinder equates to more heat transfered to the coolant but on the order of 5% or so. The danger of too much timing under load is the heat soak in the cylinder causingit to scuff the pistons and cylinder.



You should see more heat in drive than OD, more rpm's equal more fuel and more heat to dissipate.



The temps you have posted so far sound pretty normal. With a 518 the engine is always a heat sink no matter how many coolers and deep pan you put in unless you completely remove the fluid-to-fluid cooler.



Under a load and in hot weather my 92 has always run in the upper end of the gauge, like 1/2 way to the 3rd mark which translates to around 220degrees IIRC from the gauge I tested it with. With 300k it doesn't seem to be an issue. Sometimes its a driving experience to keep EGT's, engine temp, and trans temp in check.

Thanks. I'll take the truck for a run and see what it does!