Overheat during Steep Highway Climb

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Wul
1.8 8v
Posts: 49
Joined: Fri Jan 10, 2020 11:47 am
Location: Bandung, Indonesia

Overheat during Steep Highway Climb

Post by Wul »

I'm posting this to share my findings, not really meant to ask any question but you're welcome to leave your thoughts :mrgreen:

In the last few years of owning my 2.0 petrol D9 (RFV) the water temp gauge always stays above 90 (around 100 to 110) while climbing a 6% grade highway (which I read somewhere is the max grade for highway) on the way back to my home city.

I have tried many things short of replacing the radiator itself: from replacing the thermostat, checking both cooling fans, and flushing the cooling system with Prestone Radiator Flush and letting it sit inside for 5 days (instead of just 15 minutes then drain). Outside temperature according to MFD is around 35ºC during day (95ºF) or 29ºC during night (84ºF). So what I usually ended up doing is try to drive through there at night, at least it helps to keep the temperature gauge around 100 instead of 110.

Until one day I stumbled upon this video: https://www.youtube.com/watch?v=M-X4rzgxUHI and in the comments someone mentioned about how they should "give the engine some revs". I realised that this entire time I tried to keep 2000 rpm or lower, which is pretty low considering the grade. I'm driving an automatic so if the car think it's fine to stay at 4th gear at 2000 rpm I didn't question it. I thought that if the cooling system cannot cool a 2000 rpm engine, how could it cool down a 4000 rpm engine. But it does makes sense that in higher rpm water pump are also pumping faster, so more coolant flow. During the climb my gas pedal position (probably) is around 50% and if I push the pedal up to around 80%, the car would not get any faster, only after that does the car want to downshift to 3rd gear and the pedal feels responsive again. I had watched some videos about lugging the engine, but I didn't realise that what I was doing was lugging. Because both of those considerations, that's when I decided that there's no harm in trying to add more revs.

So, during the last trip, it was afternoon but just rained so outside temperature is 32ºC (90ºF). Just before the start of the hill I press the sport button so the car would know to shift later than usual. At first I'm not comfortable by staying at 3500 rpm (at 3rd gear instead of the usual 4th), but I'm already dedicated to test this so I can't back down now. After 10s of kms (out of around 30 km total of nonstop hill) the temperature gauge is still steady at 90, that's when I conclude that all I need was more rpm all along. The gas pedal feels much more responsive now that I enjoy driving one of the car that can climb effortlessly while many other cars I passed seemed really struggling to maintain their speed (most starts to gradually slow down as the hill progresses). At the end of the climb, the temperature still stays at 90. It was confirmed then that my overheating problem were because not enough rpm.

TL;DR During steep hill I usually drive at 2000rpm and it overheat, once tried to drive at 3500rpm+ it no longer overheat
2001 406 D9 2.0i 16V 135 - planning to use it for at least 6 more years
1998 306 N3 1.8i 8V 103 - has been asleep for 8 years now
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