Temperatures on Inclines vs. Declines
 

It is reasonable to assume that when climbing a hill, more load is placed upon the engine, and temps are very likely to increase. This has always been noticed on the 13b and the 20b, with coolant temperature sensor placed at the top of the coolant filler neck.

However, it almost appears unusual the rate of increase in temps recently in response to inclines.

For example, climbing a hill last night at very very very low speed as traffic was backed up. Moving nearly 20mph average, hardly any throttle is being used. So as far as I'm concerned it seems as if load on the engine can't possibly be much higher than usual flatline driving. Temps climb from 185 to nearly 210F rapidly with fans on. As soon as the car reaches the top, temps crash to 180 in nearly 60 seconds

In traffic, 20mph, flatline driving temps would never exceed 190f


So, is this just normal loading of the engine via incline causing higher temps? Or is it possible that there is something else going on here; Gravity putting resistance against the water pump? Hottest coolant moving towards the filler neck as radiator is higher from the incline etc?

In other words, the temperatures seem excessive for the perceived load. Now if you're boosting up the hill, giving lots of throttle, thats a whole different story.


The car does great on the interstate. 175F rock solid in 80F temps. But as soon as you encounter a hill, even on the interstate, up, up, up the temps go until you hit level ground. Even if you use less throttle, go slower.

What are your AFRs and EGTs when driving up the hill?

When climbing the vacuum will be less (could even be 0 depending on incline) then cruising on level ground, so it is probably a matter of tuning that area of load in the map.

Your front mounted IC may be blocking the airflow to the radiator. Going Vmount helped a lot on my temperatures.

this may be a long shot, but could it be air in the system? steam gets much hotter than water and it can make your temp sky rocket in incline if steam pocket gets to where the coolant temp sensor is. if your pressure cap is in the stock location and functions as it should, this probably isn't your problem. how's your oil temp?

These are all good points.

I do not have oil temp gauge so I cannot measure. Nor do I have EGT.

I can tell you that AFR up hill in off boost climbing is not any leaner than a 12.9-13.3 in most cases

I think its just lack of water flow, having to go through the triple pass radiator and fight gravity up hill. I may try out an EWP. Obviously, the fmic majorly blocks airflow, decreasing efficiency tremendously, but I want to exhaust all options before v mount or w2a.

All good and valid points. No. 1 contributor is airflow through the system, which points to front mount as biggest culprit (IMO). You might also try increasing your water to EG ratio. Mine used to heat soak significantly until I switched over the V-mount setup. The switch was a night and day improvement.

Not sure what you're currently running, but switching to 80% water and 20% EG should help bring the temps down. What temp are your fans coming on? 86 to 90C would be my recommendation. Also, make sure the radiator and front mount is properly ducted with all passages blocked where incoming airflow might escape, thereby forcing as much of your incoming air as possible through the IC/rad assembly. Shine a drop light around your assembly at night, and if you have light gaps shining through, you can get long strips of square AC window mount foam at ACE hardware that you can stuff in small gaps and openings to seal things up tightly!

Good luck, and keep us posted on your progress!

For an oem setup, nothing will beat the 20b and fc water pumps however, since your running the fd setup, you may also consider upgrading to that newer impeller style fd water pump with the swirl vanes. I run a rebuild 20b water pump with dual 180 degree stats and it takes much longer for the temps to reach into the 200's vs the old fd pump when the stats opened. The 20b and fc pumps are vane style. The original fd style pump doesn't have enough surface area on the impeller to move water that well at low speed. Plus you have some major resistance with your tripple pass radiator that doesn't help.

I am laughing because people on this forum didn't believe me that going up mountains is more strenuous than tracking the car at sea level on flat land in 90 degree weather.

My car used to overheat going up the mountains here in CO (ran fine at sea level). It could overheat in like 300 ft going up a large grade slow. The grades are super steep and the air is very lean meaning the engine is stressed and with 30-40% less air the heat exchangers cannot cool nearly as well. I had to stop 3-4 times going up a large mountain here when I first got the car, as soon as the car gets on top and goes down hill the temps would ROCKET lower. I mean rocket to 76C as the car is being dragged down the hill.

I attribute the lower temps to the no fuel being added to the engine and the engine just pumping air through it cooling it from the inside out, plus the speeds are much faster going downhill on an 8% grade than going up it at 30-40mph in 3rd gear in traffic.


Old set up when I purchased the car.
1) No thermostat.
2) FMIC and upright radiator unducted
3) unducted single oil cooler touring model.
4) stock turbo's


Changes made to make it better
1) dual oil coolers ducted
2) ducted radiator.
3) remedy water pump.
4) single turbo upgrade.
5) Added 182/3F thermostat.

Car ran good. car would have the fan kick on when driving slow, the faster I drove the car the cooler it would get.

My final set up ended up being by far the best.

1) 182/3F thermostat
2) Remedy water pump
3) V-mount, Both seal ducted 100% getting 100% fresh air
4) dual oil coolers ducted 100%
5) Intake in mouth of front bumper and getting ambient air
6) Water injection
7) Huge intake filter (lower pressure drop).

I am creating exit ducts for everything as well right now. The car is about 0-5F degrees over ambient for intake temps. When boosting it can drop at or below ambient. I open the hood of my car and I can grab my hot side intercooler pipe and it is cold. Getting cold air into the intake does wonders. I also ducted above my intercooler to blow the used air over the engine by the fuel injectors/ignition coils, etc and this seems to cool the engine components up there. It also reduced drag and lift. The colder temps also reduce the pressure ratio the turbo works at.


I suggest you start thinking about ducting. you only need about 1/6 the inlet size of the surface area of the radiator for the opening. You want to do a 100% ducted/sealed design so the heat from the exchanger sucks through the small opening. you also need to think about ducting the rear of the heat exchangers. This will "suck" air through them. general rule is to have the opening of the heat exchanger be smaller than the surface area of the heat exchanger, make the duct as long as possible and smooth bends opening to the face of the heat exchanger, on the back end use the same principals and make the duct exit 110% the inlet opening roughly.

Thanks you guys.

Unfortunately, I have already sealed and ducted the radiator the best I can...I've even opened the bumper up so that air will be allowed under the intercooler directly to the radiator and that passage way is sealed as well.

The only thing that may help is to increase fan capacity / or water pump to compensate for lack of airflow. I do not have the funds for a v-mount and temps arent bad enough to justify all of that at the moment.

I'm thinking of going EWP, controlling it with PWM through the ECU

Also, same with the above, the faster I drive the car the cooler it gets. On flat ground it will drop to 180F in no time. But come up on a hill and you're doomed

The 20b is just one HOT potatoe

One of the guys here put a fan on his oil cooler. You could put some fans on the back side of your oil cooler(s).

bringing this back i wanted to know if anyone knows what the CFM on the rx8 fans or 99 spec fans are i see a bunch of stuff about them when i search but every time someone asks about CFM they get no answer i know they pull more air just don't know how much

I use rx8 fans. I wired 2 fans (radiator and a/c fans) together so they both kick on when the temp is high. at 95-105 *F ambient, my oil temp stays below 180*F at cruise and goes upto 190-200*F at long idle. I'm using PWR 26x19" radiator mounted vertically with the top 5-6 inches blocked off by the frame.. my bumper opening is pretty small too.

^This is about the same situation as here. Except the temps will climb to 220F on extended hill climbs, then crash down to 190-180 immediately as the pitch goes downward!

I've since installed the EWP and there's only slight improvement. However, it is nice that the car can be shut down when it hits danger zone and cool down immediately rather than continue to heat soak / climb.

Stickman, do your temps climb up hills?


Whats peculiar is that the water temperature is being measured by the Defi sender at the filler neck. If comparing these temps to the temps at the lower radiator hose, from the EWP's thermosensor, the EWP always reads about 20F lower temps, and less volatile changes. The EWP sensor always slower to react to temperature and stays around 160F while the top reads 180F. I wonder if the filler neck is just not so much of an accurate picture of the entire temperature.

It still reads cruise temp when climbing mountains. I personally haven't experienced increasing temp when going uphill.

EWP will read lower because it's after the radiator? Your radiator is supposed to take off about 20*F, so that sounds about right to me.

and what temp are you referring to? I was talking about my oil temp... I use my stock gauge for water temp. the needle is always pegged at the "normal" range for my water temp, which isn't saying much given that it's the stock gauge, but I never had coolant issues. knock on wood.

are you talking about the little threaded holes just behind the water pump housing? that's where I have my coolant temp sensors-one for stock gauge and one for ecu. I can take it to the uphill with the laptop hooked up so I can check the coolant temp more accurately this weekend and let u know.

btw, this may be a silly question, but does your AFR change on uphill cruise versus on flat ground?

what front mount are you using?

i can't find CFM for these fans anywhere lol

Referring to water temp. Last night for example, 87F ambient, flat driving at around 195F, start hill climb, top of hill it reaches 205F, then descending it drops to 185F, then level ground back to 195F

I've tapped the neck coming off of the thermostat going towards the upper rad hose

IMO, Vmount would certainly help!

just came back from a long drive. I kept an eye on the microtech sensor readings. My water temp is pretty steady at 83*C regardless of downhill or uphill. That's about 180*F. My water temp sensor is in the stock location (just behind the water pump housing). I can't be in boost now because there's something wrong with my tune, so this was on vacuum cruise. Ambient is 95*F.

on a side note, I noticed my MAP sensor reading is little erratic, reading 0-2"hg back and forth when the engine is off. is this normal?

it def will but seems like monster is having trouble at idle and up hill not on the highway which is more of a fan problem