I have an '02 with the Mugen cooling mods, and now that it is getting colder, I've noticed that my temp gauge bounces between 3 and 2 bars. I knew that it was taking longer to reach 3 bars because of the colder weather, but couldn't really figure out why it would go back to 2 bars on some occasions.

I had a 45 minute drive on the way home from work this evening, and I discovered something surprising. It was 50 degrees F, and it took about 4~5 miles and a few stop lights to reach 3 bars. However, for the next 30 miles and probably 15 stop lights after that, I noticed a very obvious pattern. If I stayed at 5K RPMs, my gauge would quickly drop to 2 bars, until the next stop light, where it would always return to 3 bars. This happened for the entire drive!

I came to a 2 mile stretch of open road after a light, where I got up to ~60 MPH in 4th gear, waited until it dropped to 2 bars, then put it in 6th gear. It only took a few seconds for the gauge to go back to 3 bars. It would not drop to 2 bars until I put it back in 4th gear.

I don't really know that this discovery means anything, but I'm curious about a few things. Where is the sending unit for the temp gauge? I realize that it is probably due to the fact that the water pump moves more coolant at higher RPMs, but I'm curious if it is actually cooling the engine more, or if it is just fooling something.

If it is actually cooling better, then it seems that it would be a good idea to do a long, low load, high RPM route back to the starting grid at autocrosses.

 

Guys with water temp guages can probably tell you if they have the same experience. From my own experience, I've never bounced back to 2 bars if I've reached 3 bars.

I'll have my guages in soon hopefully and will be able to tell if water temp decreases with higher rpm runs on the highway.

 

at higher rpms the coolant flows faster thus dumping heat faster? the Mugen thermostat opens at lower temps which may lie on the threshold temperature that is designated as the 2->3 bar transition on our gauges.

IMHO, unless you're upping the compression on your motor or running it at high RPMs all day, these mods may not really be something you want. The engine needs to remain at operating temperature. I don't see the constant temperature variance while driving as positive improvement over stock.

 

[QUOTE]Originally posted by SECRET AP1
[B]at higher rpms the coolant flows faster thus dumping heat faster? the Mugen thermostat opens at lower temps which may lie on the threshold temperature that is designated as the 2->3 bar transition on our gauges.

 

230F at a stop?!? That's too high. Normally coolant temps will stabilize around 200-210 while idling on a moderately warm day.

But the reason the engine is getting cool is indeed rpm. When we need to cool a car back down on the dyno, we bring the revs up to flow more coolant and it works very rapidly. With a cooling fan, the A/C fans on and the engine at 3k-4k rpm we can drop coolant temps from 200 to 180 in 30-45 seconds. Even with a stock cooling system setup, we can get it down into the low 170's if we let it keep going that way.

On the road you've got a lot more airflow through the radiator (and very cold air right now apparently), so how well it cools will depend on engine rpm and total airflow. If you were actually at full throttle, temps would go up, but at light loads, higher rpms really don't create much more heat.

UL

 

Thanks, UL. I was hoping you would drop a note.

I was amazed that the temp went up that high at the drive thru, since it was in the 50's at the time. The only explanation we could come up with was that we had been driving pretty hard just before pulling in to the parking lot. The temps were at around 170 when I pulled in, then 2 minutes later, we looked at the scan tool and it said 230. It peaked out, then started dropping again. After leaving the drive thru, it dropped back to the 160~170 range quickly.

 

did you get all the air out of the system? you shouldn't see temps above 220ish as UL said, fans kick in around there to cool things down.

 

The fans only kick in if the radiator gets hot. That is why I asked where the ECU gets its temp readings. The temp gauge on the dash never went above 3 bars. It was just indicating 230 on the OBD-II scan tool for about a minute.

 

I had my Defi gauges installed today thanks to the guru, xviper. When I was driving aroung town the coolant temps was pretty steady at 82C or 180F

For my oil pressure it maxed out at 600Kpa and idle at 200Kpa.
Even when I vtec the pressure doesn't jump past 600Kpa but I only got up to7800rpm.

 

Damn, Pokey! Were you stuck behind a school bus or something?