Coolant temperatures while towing

Recently I towed our 5500 - 6000 lb camper with our 1996 K2500 Suburban 7.4, with 4.10 gears and a 4L80e trans; once to the mountains in NC, the other to the camper dealer near Richmond.

Towing speed on both trips averaged 65 mph or below, in 3rd gear, as advised by the shop that recently rebuilt the transmission.

On the trip to the mountains, coolant temp stayed just below 210º, and maybe a bit more a couple of times. Air temperatures were mostly in the high 60s and low 70s. On the trip to Richmond, air temp was around 87º, and the coolant temps hung around 216º, and got up to 225º indicated, and confirmed by an OBD2 dongle.

We have a couple of upcoming trips in June and July to the mountains in VA, and the air temps could easily get into the 90s at lower elevations. The question is what is the acceptable coolant temperature range for the 7.4L while towing? The highest I’ve seen it go is 225º, and that was in rolling terrain on the interstate.

Maybe I just missed it, but searching through the GM SM I couldn’t locate a definitive “normal” coolant temperature range; nor could I find a temperature at which the engine is considered to be overheating.

Can anyone here shed some light on this?

I don’t have one but have read 220° is right on the edge of safe limit. I’d be nervous even running it too long there.

Caman96 said:

I don’t have one but have read 220° is right on the edge of safe limit. I’d be nervous even running it too long there.

Normal 4L80E temp?

I plan on doing some serious towing with my 1992 K2500 454/4L80E/3.73 4x4 Camper Special, towing an enclosed trailer that is about 10,000lbs. The truck has a heavy duty radiator with incorporated engine oil and trans fluid cooling. I am assuming (?) the engineers knew what they we're doing...

www.gmt400.com

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Thanks. I read the thread you linked, and it appears that they’re discussing trans temperature, not engine coolant temperature. I have no way of determining trans temperature, as my scan tool and my OBD2 dongle won’t read trans temps.

did you happen to be running A/C?

VA I apologize, I started reading and instantly associated towing/temperatures with transmission!

South VA said:

I have no way of determining trans temperature, as my scan tool and my OBD2 dongle won’t read trans temps.

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I know this thread's about engine temps, but if you want to monitor trans temps that topic was covered recently in this thread below, using an OBDII bluetooth adapter and a cheap smartphone app:


As for coolant temps, a 15# (psi) radiator cap w/ 50% ethylene-glycol and water mix yields a boiling point of 268F, which is where I believe most temp gauges go red. You likely already know this.

Where can you be comfortable in that range, between ~200 (themo opens) and 268? Let's see what others say. For me, once the gauge is beyond "12-noon" position I get antsy.

Tomcat71 said:

did you happen to be running A/C?

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As a matter of fact, yes.

Caman96 said:

VA I apologize, I started reading and instantly associated towing/temperatures with transmission!

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No worries. At some point I’ll install a trans temp gauge as well.

South VA said:

As a matter of fact, yes.

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On my 1998 L31, the ECU will disable the AC when coolant temps exceed a threshold of ~124C (256F) as a means of mitigating high engine temps.



If you've got the auxiliary cooling fan option, the ECU will kick it on/off as engine temps cross certain high and low thresholds (much like the AC, above); I don't have the OE values to report here.

1998_K1500_Sub said:

I know this thread's about engine temps, but if you want to monitor trans temps that topic was covered recently in this thread below, using an OBDII bluetooth adapter and a cheap smartphone app:

Bluetooth OBD2 adapter

ive used OBDLink products https://www.obdlink.com/

www.gmt400.com

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My understanding is that the ‘96 doesn’t have the capability of reading trans temps via scan tool or OBD2 dongle. In later years, yes; the ‘96 was a transition year, apparently.

Of course I could be mistaken in this, and would like to find out otherwise. But so far, I haven’t.

1998_K1500_Sub said:

As for coolant temps, a 15# (psi) radiator cap w/ 50% ethylene-glycol and water mix yields a boiling point of 268F, which is where I believe most temp gauges go red. You likely already know this.

Where can you be comfortable in that range, between ~200 (themo opens) and 268? Let's see what others say. For me, once the gauge is beyond "12-noon" position I get antsy.

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That’s why I posed the question. On the analog gauge the temp reads a couple of ticks above 12 noon, and the OBD2 dongle gives me just about the same reading.

1998_K1500_Sub said:

On my 1998 anyway, the ECU will disable the AC when coolant temps exceed a threshold of ~124C (256F).

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Good to know. Don’t know if my ‘96 does that or not. It would be a nice feature to have.

It turns out it does have an electric auxiliary fan. What I don’t know is if it is working, and I’m not sure how to tell.

FWIW, it only stayed at 225º briefly, a couple of times, then came down to 221º, and even 216º when I slowed down by 5 mph.