overheating rb25- done search, but still open questions

[s13_rb25det]

hi,

i have an rb25det swapped into my s13... i have a aluminium koyo installed which is not leaking and have bled the system with this screw near the TPS (by taken the screw out until the water began to come out - is this correct?)... i have a strong 2300ccm puller type fan installed between koyo and engine and a 2000ccm pusher fan between FMIC and air-con cooler pushing the air towards the koyo...

engine is overheating no matter if stuck in traffic on a hot day or also just driving along on the highway... no matter what in which situation, it still overheats and its beginning to piss me of slowly...

i had a nismo 62 degrees thermostat installed, but engine was still overheating so i removed the thermostat and have none installed now...

could it be that the overheating is caused because the engine bay space in an 240sx is very little and the hot air has no-where to escape? i must also mention that i have a large FMIC and air-con cooler installed infront of the koyo... could this be a problem?

maybe somebody has an idea how to get this problem solved...

thanks

[madcowvert]

maybe your water pump went bad.

[lazyboi444]

Yeah try the water pump..Well in most radiators at work i have seen where some air pockets will not come out at all..And the radiator has to be vacuum bled. Do you have a Aftermarket temperature gauge or the stock cluster one? What temp is it reading?

[USMCgetsome]

OK homie i had the exact same problems. Heres what i did to correct. I would suggest draining all the coolant in the system and then simply purge the lower block and upper block water passages by pushing fresh water from a water hose into the system. Ensure u have an upper and lower hose open so the water can drain.

After i did that i plugged everything back in and filled the motor from the thermostat neck till full. installed my new nismo t-stat. Connected upper hose and then filled again. After that i purged the same way u did by opening the bleed but i ended up pouring in more coolant in that small hole. Then started the motor watched the t=stat open up and purge coolant from bleed screw. Steady flow then filled again at the bleed screw.

Kept doing that till i felt it was full. Then drove it around and VIOLA. Issue solved.

I have a koyo and one 14in pusher and slim 12in puller for fans and a fan water temp controller. It regulates temperature very well. Love the system. Since then i've been good.

Had that issue for about 6 months till i got off my butt and listened to these guys and bled the system the right way.

[Tripz]

I'm not sure if I have the same problem. After driving around for approx. 30-40 mins, the water temperature reaches 90-93 degrees cel. Is that normal? Would that be consider overheating? I also have a KOYO rad and 2 dual pusher fans.

[kouki-gymkhana]

I was having the same problem a while back. Looks like you forgot to mention if you have any ducting to force the incoming air only through the radiator and not around it. I have the same cooling mods but some well-placed holes in the bumper and ducting above and below the radiator really helped the situation. After all of these mods, I'm seeing ~80-85 C in stop and go without the A/C on on a 94 degree F day. With the A/C on, the temps quickly get as high as 95 C. I think the problems are ultimately due to the following:

1. If you have kept your A/C condenser in place, it really restricts a good bit of the incoming air, especially if you have a big FMIC in front of it.

2. If you have your A/C hooked up and are using it, the condenser gets VERY HOT! and can increase the ambient temp between it and the radiator by more than 70 degrees F. At that point, it doesn't matter how much air your fans can move because they are just moving MORE hot air.

3. The frontal area of the s13 240sx is arguably TOO small to effectively cool the RB25, especially if you haven't added any holes to the bumper. If you need proof, just look at a couple pictures of any R32, R33, or R34 skyline in profile and you will see that their front ends are much taller and punch a much larger hole in the air than the wedge shaped s13.

My advice to you would be to bleed your cooling system very thoroughly, make some underbody ducting, add a bottle of water wetter or another similar product to the coolant, and seriously think about cutting up your front bumper to allow more air to get to the radiator. If all of that doesn't help, you might want to consider a leakdown test to see if you have a blown or leaking headgasket.

Good luck...-KG

[Tripz]

What kind of ducting would force the incoming air through the radiator? I have a cooling panel for my s13 but it doesnt fit because of my Seibon carbon fibre hood. I've bleed my cooling system today, did a coolent flush and ran distilled water through my radiator until I see clear water from my drain plug. I filled it with 50/50 antifreeze and took it for a spin. Drove it around approx 45mins and during stop and go it would reach ~81-87 C. I've then drove it a little harder than i usually would and the highest it reach was 90 C. Please keep in mind that the sun was setting and it was around 18 C (~64 F). I'm scared that if it was a hotter day, say 25 C, that it would reach ~95 C. I do not have A/C or turned on any heating of any sort. My main question is, what temperature do I have to reach to be considered overheating and harming the engine? Sorry for all the questions but I had this problem close to a year now.

[Coolwhip]

number 1. Put a thermostat back in. Try using a regular thermo instead of a Nismo. The problem with the nismo (in some applications) is that it opens too early for the coolant in the radiator to have cooled down properly and exchanges it with the hotter coolant in the engine. So you hardly keep the coolant in the radiator long enough to cool it down. Same goes with the "NO THERMO" setup where the coolant system is constantly curculating and the coolant doesn't have time to sit in the radiator to get cooled.

The higher temp thermos will allow the radiator supply sit longer resulting in cooler coolant when the thermostat opens.

The area around the radiator and condensor has alot of gaps for escaped air flow. Same goes to when you have a FMIC the air gets diverted with all that mess in front. And just like they said our S13 fronts are way smaller and wedged compared to the MACK truck style fronts of a R-Chassis

[Cpt_Impossible]

I have a 20 and have struggled with heat issues since the swap. What you will notice when you look at the skylines is that they have a vent in between the headlights to allow air to hit the top of the radiator. The 180sx style front doesnt have this unless you use a pignose bumper and cut out the vents. Even then, its a small amount of air. The RB loves to trap air though, park on a steep hill nose up and run the car for a while, then cool it off and let the air bleed out the bleeder screw, repeat until you don't loose any.

[Cpt_Impossible]

You can see what we are talking about here, there is a hole so that air reaches around air con and touches straight ont he radiator, there are also seperate vents for smic.

I'll share some of the efforts that I have taken:

Cut out the pignose



Rigid Racing Upper cooling panel

Custom Lower cooling panel



Made a cold air box for the intake so it wasnt sucking in the turbo's hot air



I run a Koyo filled with 75% Distilled water 25% Honda Blue coolant and a Bottle of water wetter

2 12" pusher fans

Took the weather strip out of the back of the hood and am considering spacers.

No air con system but I have a dual pass FMIC in front of the radiator

The RB's seem to be a cooling mess for some and others get away with nothing, I don't really understand it.

[Cpt_Impossible]

Oh, also, make sure that when you bleed the system, you have the heater on full blast hot so air isnt staying in the heater core. Also, if the radiator cap is old like it came with the motor, make sure you get a new one in case it isnt holding pressure.

[mello88]

OT: ^^^ Your lower rad panel and air box look great. Do you have any ducts on the sides of the rad? Also on the airbox, what did you use to line the edges with? Looks like some kind of split (vac?) tubing.

[Cpt_Impossible]

The edges are lined with split tubing, i started with vinyl, but it was hard to form and keep in place while the glue dried so I switched to rubber vac line. Just carefully run a blade along the inside.

The sides are the only part of the radiator without ducting. When I cut the bumper vents a bolt snapped while putting the bumper back on so I have to get that out before I can remove the bumper next time. I think I am gonna just duct the passenger side as I used the drivers side to feed my airbox.

[s13_rb25det]

i just did a draft write-up of how to bleed the system correctly... will add some picts later on... please correct any mistakes:

1. Empty out radiator, disconnect water hoses and open the radiator cap2. Open the screw in the block next to the turbo and bleed there aswell3. Remove the thermostat and aluminum piece on the head4. Screw the screw on the block back in5. Pour (distilled) water through the place of the thermostat and let it run down through the block until you see clean water6. Connect the lower hose to the radiator and continue pouring water and anti-freeze (1:1) through the thermostat hole until system is full7. Attach the thermostat back to the head and screw the aluminum piece over the thermostat using some kind of sealant8. Connect the upper hose9. Screw the radiator cap back on10. Fully unscrew the main bleed screw (next to the TPS) 11. Start the engine and put the heating on hot and maximum blow12. Pour 1:1 mix through the little hole until the engine and radiator are full13. Screw the bleed screw back in

Theoretically this should get the temps down.