What are normal Gen 4 engine temps when under load?

[BoulderCharles]

I have an LC9 in my Land Rover Discovery 2 (5.3L Gen 4). Around town, I?m at 200-210, even on 95 degree days in stop and go traffic. Going up the shorter, steep mountain roads here in Colorado, I get to 215-220. Going up I-70 (at 65mph and a steep grade), it quickly rises to 230 but drops pretty quickly when I turn around (even as low as 190 when coasting downhill). I know the stock GM ECT gauge goes all the way to 260 and GM doesn?t max out the second fan until 235 or so (in the stock tune) so I?m trying to understand if this is normal for Gen 4 truck motors or if something is wrong.

I have replaced the stock radiator with a 2-row aluminum version with dual fans and a shroud. Thermostat is a new 170-degree unit. Water pump is new AC Delco. Coolant is new and refilled with a vacuum system to get rid of air pockets. I also tested for a combustion leak (aka head gasket leak) and all is good there.

[mbray01]

Are you measuring temperature, or using the scanner pids
the oil temp is calculated based on engine temp and load, so exactly what you described would be normal, increasing temp with load.
If your measuring oil temp with an actual sensor, than 35-40 degrees over coolant temp is normal. oil is good at absorbing heat, however its not very good at shedding heat

[BoulderCharles]

This is engine coolant temperature and I'm measuring via CAN-bus PIDs (with a scanner tool and via 0x05 PID for my ECT gauge).

[blindsquirrel]

Measuring at only one location (the factory ECT sensor) is not enough to tell you what's going on.

[BoulderCharles]

Gotcha. I could put another ECT gauge in the radiator as there is a port there. If the temps are lower elsewhere, that would suggest air trapped in the head, right?

[blindsquirrel]

There will usually be a not-insignificant difference even between the front half of the engine (left head) and rear half (right head). You really need to see temp at the water outlet (or radiator inlet) and radiator outlet at the same time.

Also, I bet you would see a lower max temp under load with a higher temp thermostat. I always have.

[blindsquirrel]

Are you using the stock truck '2 corner' steam vent pipe thingie? On the front steam ports?

[BoulderCharles]

I was running a stock thermostat up to this point (187F, I believe) and didn't notice a difference when I swapped to a cooler thermostat.

blindsquirrel, what do you see as typical max temps under high load?

[BoulderCharles]

Are you using the stock truck '2 corner' steam vent pipe thingie? On the front steam ports?

I have the stock steam vent pipe at the front of the engine, with the steam hose run to the bottom of the expansion tank.

[smokeshow]

Thermostat just sets the minimum coolant temperature. The fans are responsible for the maximum. Or the shrouding in the front of the vehicle if you're at speed. Eisenhower grade can definitely put a cooling system to the test in the summer.

[BoulderCharles]

Question for the experienced tuners here. Does the "Vehicle Speed Hi" setting fully turn off the fans above the set speed (which is currently 40mph)? If so, that might explain why it is heating up so quickly at highway speeds.

[blindsquirrel]

Granted, I don't live within a day's drive of anything that could be properly called a mountain, and I don't live at altitude, but my truck doesn't show any coolant temp change at all based on how hard it's driven. A/C on full blast will push it up from the normal of 198-199 to 208-210 but I could probably fix that with more aggressive fan settings. And this is a V8 Envoy, which GM built with the leftover cooling system from the 4.2L 6 cylinder.

[BoulderCharles]

In doing some more research, I do think the "Vehicle Speed Hi" is inadvertently turning off the fans above 40mph. I have discrete fans so while the ECM thinks its just slowing down the fan speed above 40mph, I think it's actually lowering the commanded fan speed enough to turn them off. It will be a few weeks before I can test this but I wanted to share the hypothesis in case someone is dealing with a similar situation.

[gtstorey]

I wouldn't think fan speed would matter much at highway speed.

[blindsquirrel]

Thermostat just sets the minimum coolant temperature. The fans are responsible for the maximum. Or the shrouding in the front of the vehicle if you're at speed. Eisenhower grade can definitely put a cooling system to the test in the summer.

Yeah, true, but only if the cooling system has enough capacity to keep the coolant at the lower temp without the t-stat already wide open and fan at full speed under light load conditions. If it's already maxed out before you head up the mountain, temp will climb when load increases. A higher temp stat leaves more system capacity in reserve so there's less spread between light load temp and heavy load. At least that's been my experience, I've always seen more stable coolant temps with a higher temp t-stat.

[alanwparkerap]

Blind squirel you helped me a while back on maf tuning could you look at the timing thread I posted like one or 2 under this thread and tell me what you think about the timing I added. I loaded 2 tunes one stock and one with changes as well as a log

[smokeshow]

Yeah, true, but only if the cooling system has enough capacity to keep the coolant at the lower temp without the t-stat already wide open and fan at full speed under light load conditions. If it's already maxed out before you head up the mountain, temp will climb when load increases. A higher temp stat leaves more system capacity in reserve so there's less spread between light load temp and heavy load. At least that's been my experience, I've always seen more stable coolant temps with a higher temp t-stat.

That's why it's just the minimum I wouldn't say it's a matter of reserving cooling system capacity though. You might be able to cool the fluid in the radiator off more by maintaining a higher ECT, but only at part load. Start working it up a hill and that's gone in seconds though. Once you reach the maximum capacity of the cooling system to exchange heat with the environment, temp must increase. This is why every modern vehicle on the road has derating features to prevent sustained load from over taxing the cooling system.