rb25det overheating issues!!

[tylerd10230]

ok so i have just ben through hell and back with my rb25det swapped s14. and my problems never seam to end. i go and replaced maf sensor, both knock sensors, the harness for knock sensors and then the coolant temp sensors becouse the car was having extremely high egt's drivign around and then was overheating. well solved the high egt problem but know my car still ovewrheats . car runs perfectly fine until my water temp reaches over 180f then it slowly climbs to 220f and never goes any higher. i have 2 fans 1 primary 12in fan and then a secondary 12in fan. i went and set both to come on as soon as car reaches 120f so i could hopefully keep the temp down but it didnt solve to much of my problem .
things ive noticed/done:
primary fan wont cut on sometimes and if it does it comes on half powered.
secondary fan is on full blast!
turn fan thermo all the way down so they both stay on at all times
new coolant temp sensor
new gauge sensor along with water temp gauge
a/f is 15.8 at idle
egt is 600-750 at idle
brand new stant 170f thermo for 300zxtt
50/50 coolant/water mix
bled coolant system
after engine shutoff i hear a girgling noise coming from heater core lines. (sounds like water being pushed back into engine )
ZERO COOLANT LEAKS
NO OIL IN COOLANT / COOLANT IN OIL
PERFECT COMPRESSION!!!

VENTED HOOD!
i honestly feel like its a air buble in cooling system but im not sure at all becouse ive bled it till the bubles stop coming out and thats in my steep ass driveway! also car stayy steady at 220f when running and driving for 30min and it gets to 220f very quickly
!!! please help!



considering adding 2 pusher fans in front of ac condensor to push air to the puller fans i have behind radiator. could that help cooling issues alot?

[Sileighty_85]

sounds like air bubbles if your hearing a gurgle when you shut off the engine.

Mine stays around 80-93*C (176-199*F) when its close to 100* outside
I can make it run cooler if I adjust the fan controller.

I got
Koyo Rad
N1 Water pump
Nismo Thermo
Dual FAL
DIF PWM Fan controller

[tylerd10230]

o ok well ima try jacking my front end way off the ground in my steep driveway and bllede it like that so my radiator cap is def the highest point.
mods list is :
greddy intake mani w/ q45 tb
koyo rb radiator
2 12' puller efans ( cut radiator support)
170degree stant thermo
fans both run at all times
retained factory ac ( no fANS IN FRONT)

IM GOING TO INSTALL 2 PUSHER FANS 2MORROW MORNING and rebleed cooling system as well in hopes of fixing problem as well as cooling problem

[Sileighty_85]

I have A/C in mine as well running pushers in front of the condenser

What Kinda fans are you using?
They might not be pulling enough CFM

[tylerd10230]

thats what i wa thinking but they r flexalite fans 2 12'in pullers but thats why im going to install 2 10in pushers 2morrow mornign cuz i figure if i run 4 fans it could help quite a bit becouse ill have 2 pushing alot of air and 2 pulling alot of air so itl cool the coolant down faster and make it run better.
i dont think the fans that i currently have are pulling enough cfm at all. thats why i wanna install 2 more fans plus this damn weather where i live is retarded its been humid as hell and in the mid 90's all week and my car hates it

[abunai the drifter]

you have an air pocket in you cooing system jack up the fornt of the car and add coolent aand watch for bubbles an if your rb has a bleeder screw open that an see if you have air i would buy a coolent funnel Lisle LI24610 - Lisle Spill-Free Coolant Funnels - Overview - SummitRacing.com (http://www.summitracing.com/parts/LIL-24610)

[tylerd10230]

ok thankyou for the help i hope rebleeding the cooling system helps ima jack it up enough that the front end is def the highest point and hope it works out!

[abunai the drifter]

ps turn your heater on when you do this it allows coolent to travel through the heater core.

[tylerd10230]

thats what i was doing before i had the heat on full blast and car ona hill but i didnt have front end jacked up so this time im going to jack the front end up

[kouki-gymkhana]

4 fans at once really seems like overkill, IMHO. I run 3 on my RB25 s13 with A/C and I think it's a bit redundant. I'm running a thick Koyo, FAL 210s as pullers and the stock A/C fan as a pusher in front of the condenser. I've hacked up the rad support to move the radiator further forward to fit all that in there. With 70/30 water:coolant, a bottle of water wetter, and conscientious bleeding of the system, I'm running a steady 75-80C on an 85-90F day without the A/C. With the A/C, I"m up in the mid 90C range. Hot, but not dangerously so. Since I went to a silvia front end, my cruising temps have dropped about 10C so sufficient airflow is key to keeping the RB motors cool. They inherently run hot.

I would try and rebleed the system again, add water wetter, and consider going with the stock clutch fan. My 3 fans pull CRAZY amps and clearly drop the idle a good 200rpms when they kick on. If I could do it all over again, I would just stick the stock clutch fan back in there and pull all this e-fan bullshit. I've already had a FAL fan motor die on me for no reason and the car overheated pretty quickly.

Good luck

[tylerd10230]

well as fo yesterday i foundout 1 of my main fans has gone out and died.... so only fan i have is my primary and no others . so my plan is put a factory clutch fan on and then 1 pusher fan in front of ac condensor. but i feel like my overheating proibs wiht only 2 fans were made worse cuz my fmic is so damn big it blocks all airflow from bumper. and then the dieign fan made it worse as well so i wired upa pusher fan in front of ac condesnor and im installing clutch fan 2morrow and hopefully itl solve all probs!

[carlos_spicyweiner]

Another thing i would look into would be path of least resistance in air flow if air is just blowing under the car and hitting the bottom of the rad and IC that could be your issue to (roommate had same issue) also wouldn't hurt to look into a swirl pot it splices into your cooling system and pulls coolent into it and removes air bubbles while the car is running.

[tylerd10230]

also tried rebleeding cooling system by jackign front end of car way off the ground ran the car for 30min no air came out. put cap on it then cut off. let sit for 45min then pulled cap off rebled again! never let overflow tank get below the full line. and did this 3 more times. no bubles ever came out noise from coolant hoses still there but barely can hear it . and at idle my water temp gauyge reads 220f yet my cluster gauge reads halfway at the normal spot. but car doesnt run great. its pulling timing and having probs but when first started in the mornignr uns awsome for all of 10min

[tylerd10230]

Another thing i would look into would be path of least resistance in air flow if air is just blowing under the car and hitting the bottom of the rad and IC that could be your issue to (roommate had same issue) also wouldn't hurt to look into a swirl pot it splices into your cooling system and pulls coolent into it and removes air bubbles while the car is running.

would u suggest me installing a shield underneath the car to hold the air in?? i was reading some other peoples post and saw where they were talkign about reinstalling the factory shield or whatnot that sits under the enigne

[kouki-gymkhana]

Man, you need ducting for sure! I have a big ass galvanized plate going front the bottom of the front bumper back beyond the oil pan. I also have a radiator cooling plate on the top between the headlights and the rad support. You have to direct the air through the radiator or else it will follow the path of least resistance and go around it. I don't know what front end you are running but with my chuki bumper and pop-ups, I had to put 6 3in holes in the bumper to improve airflow to the radiator. Made a world of difference but I still wasn't satisfied. I switched to a silvia front end and it dropped the temps significantly. Adding a swirl pot will help as well as it constantly bleeds the system for you. Good luck

[smoked240]

Wow. Is is weird. I have the exact problem you are having. Word for word. I get the bubbling sound at the back of the head, Reason I can only think of is the coolant is too hot. which makes sense, cause both our cars are overheating.

When I am idling with both fans on it will not go above 70C. The moment I start driving it will start heading up to 120C. I know I don't have an air bubble trapped because it would overheat at idle also.

Your problem is, your not getting enough air to it. Remove your bumper cover and take it for a spin. I did this and shut the heater off and fans off and my temp dropped from 100C to 70C within a mile. I also drove for a couple miles at 60 to see if it would slowly climb up. Nope, worked awesome.

[Bbsalexaz]

are all of your cooling mods new? Have you tested your thermostat? is it granny driving and it heats like that, or is this when you get on it.

[smoked240]

are all of your cooling mods new? Have you tested your thermostat? is it granny driving and it heats like that, or is this when you get on it.


I have a brand new N1 water pump with a brand new nismo thermostat. I am driving at a constant speed of 60 with both fans on and heat blasting in 70-90 degree weather. This happens on long trips. Once I hit town and slow down to 30 or so, my fans actually work so the heat will drop some.

[WhipsGoneWild.net]

not to jack ur thread man but...i have same prob lol

-when i bought it i blew 3 stock plastic radiators
-i flushed the system
-replaced the radiator with cx racing and got nismo thermostat and still does it
-i mean the cooling system isnt very complicated but i dont think its the pump or a block or a head gasket.
-i have 2 small (i think 10") pusher fans that run constantly (no shroud)
-my battery voltage from pfc reads 12.5-13.2 idk if thats super low
-it runs fine on the highway but when it starts to get warm >220F it tends to run lean (my car needs tune as well but have to fix overheating before i start beating on it)
-I spoke to a buddy that has 2j in s14 and said his overheated then he got 1 large fan with shroud and took care of the problem.

does anyone have any advice?

i now see there is a bleeder valve and leave it run for awhile

[radianation]

I realize this is an old thread but it has good information for troubleshooting, but nobody ever came back to update it with what their solution was?

I've had my swap for many years and just fully rebuilt it last summer after destroying the engine at a track day. Now it overheats while sitting at a stop light, even on a cool day (50 degrees ambient temp outside).

I think there may be air bubbles, but I have tried burping the coolant a few times already. I have an N1 pump, koyo radiator, dual flex-a-lite puller fans, vented hood, and I've run this setup for 7 years without overheating issues. Verified thermostat is good. The only thing I've changed since the last rebuild was introducing the Isis oil cooler. I placed the oil cooler in front of the radiator and I think that it is heat soaking my radiator at stop lights and causing the system to overheat.

Thoughts?

[Kingtal0n]

Alot of time, if everything in your cooling system is "good", the problem lies with the ignition timing.

Ill give you an example, an RB26 car was running fine with all the OEM equipment, but when the owner switched to a stand-alone suddenly he had overheating troubles. Of course your instinct is to blame the radiator/fans/air pockets etc...

It just needed a bit more timing advance. In fact, you can take a car on the highway and boost it for a few seconds, and then check the temperature rise rate afterwards, to get an idea of how much heat you are throwing away. Add a few degree of timing and do it again; if you get a lower rise rate (rate of change of coolant temperature with all else being as equal as possible) then your additional timing is throwing less heat into the exhaust, you can verify with EGT to some extent. I say "to some extent" because other factors also influence EGT such as air/fuel ratio, there is a give and take when it comes to temperature. Also too much timing will lower/taper heat output but also lower engine output, typically knock count will rise, so using the chassis-dynometer is a large advantage.

The situation may become more clear from the other point of view, that is,
Take a perfectly good running engine and start retarding the timing at WOT. The EGT will go up, the torque output will drop, the manifold may glow red in fact; And the coolant temperature will rise more rapidly. This effect can be seen at idle the same as WOT, but typically we only pay super close attention to the timing at WOT and many folks just blatantly ignore timing at idle/ off throttle conditions because the engine does not seem to respond to changes much. I'll tell you that if I had a car overheating at idle and the timing were bouncing around 12* the first thing I would try is moving it to 20-22* with an 14.2:1 air fuel ratio and see what happens.

[radianation]

Good tips, but your simple quotes around good made me rethink things... =)

Turns out, my problem was relatively simple. The plug on one of the flex-a-lite fans was cracked and it was shorting out. When I tested the fans they were working, but driving around sometimes it would cut out. Wasn't very obvious with the RPM or noise since one fan was still working just fine.

[redline racer510]

Stock clutch fan with KA radiator and it never gets more than a few degrees above thermostat opening temps. Stock clutch fan= you will never go back to electric fans. BTW rb25 fans are some of the highest cfm clutch fans that nissan makes.

[maison]

I have a rb25 e36 and also experience heating issues when sitting in traffic, only option I have is bigger fans but space is tight. temps return to normal when driving but often creeps to 220 when sitting for a period of time.

[TwoForDeh]

See, mine's backwards. It's weird. Sitting in traffic and bee-bopping around town, my temp stays right where it's supposed to be. But, once I get on the highway for more than 5-10 minutes, she starts getting hot

[Nissanhardline]

i know that this is a very old thread but i would like to shine some light out there for owners that have swapped a rb25det or rb20det in an s13 and want a cheap reliable cooling setup i have found that any dual core radiator that "HAS" equal cores inside combined with a ka24e fan clutch and fan will cool an rb25det easily. The only modifications that need to be done are that the plastic fan itself needs to be trimmed about half an inch or more on the backside because it will hit the crank pulley and wont work other then that i ground down the lip where the radiator would sit against to move it forward about a few millimeters i left the bottom mounts stock as it wasnt really close to the fan im running without a shroud and my car never overheats anymore and thats sitting in 30min of traffic infront of my college this is by far the simpliest setup for the cheap that works no bs electric fans or stock rb25det clutch fan because i also tried those the rb25det clutch fan is way to big but i got it to fit with a s14 stock rad but quickly found out that there wasnt enough room when the engine torqued under load and blew the rad apart

[radianation]

Blast from the past. (pun intended) =)

I'm still running the dual puller fans, but might be changing those to pusher when I install AC again this fall. Don't plan on tracking the S14 anymore since I have other cars for that so I'm optimistic that cooling will be less critical when not flying around a track.