STOP RB20 / RB25 / RB26 overheating!

I used to have a big cooling problem with my RB20DET in S13 swap which as far as I can tell is now gone. This is to provide some basic info and suggestions to those who have to go through the same ordeal as I did.

Did you bleed properly?

-Nissan engines are a total pain to bleed and the RB engines are some of the worst. They love to trap air in them. You can follow the factory guidelines, but here is what I do.

-Turn the heater to full blast hot and then fill the car up with coolant.

-Start the car and let it idle for like 30 seconds.

-Then remove the bleeder screw on the front of the intake manifold and the radiator cap.

-Top the coolant off and replace the screw and cap.

-Park nose up on the steepest hill you can find that’s close to your house or jack the front of the car up.

-Start the car (with screw and cap on) and let it heat up (still with heat on full). Turn the car off and let it cool down for 15 minutes.

-Slowly remove the bleeder screw. If bubbles come out, top off at the cap and repeat the warm up cool down. If bubbles stop coming out and coolant dribbles out without any air accompanying it you should be done.

-Check the coolant before every drive for the next week and top off as necessary.

Are your hoses old?

If you are using the main radiator hoses that came with the swap, you shouldn’t. These could be factory hoses from 17 years ago for all you know. Many car manufacturers put a spring inside of the hose to keep it from sucking itself shut with the suction created by the water pump after time. Nissan didn’t, so these soft hoses can be a real choking point for coolant at higher rpm’s. You can use the KA24E lower hose, or you can order one made for the RB online. Tweakit, an Australian performance website sells factory hoses for the RB’s. My lower hose cost me $32.23 to my door.

The upper hose you can just go to any parts store and get a section that fits. It’s a pretty straight line and depending on your swap setup, the length will change.

Also check all of the smaller hoses like the one on the back of the engine that goes to the heater core and the ones along the intake manifold. Any cracks can cause the system to lose pressure and also lose coolant causing you to overheat. Anything that is too soft should be replaced as well.

Is your radiator in good shape?

If you are using your old KA radiator or if you are using the one that came with the RB it may have bent fins or bent tubes that could be hindering flow. Make sure the fins are allowing air to flow through; this may involve an hour sitting with a small screw driver straightening them. Remember, be careful when doing this. It doesn’t take much to break the radiator in some places. Many people just upgrade to a Koyo or other performance radiator when doing the swap so unless you are really clumsy you don’t have to fix bent fins and tubes.

Is your radiator cap in good shape?

If you are using a cap that came with the clip or one that you are not absolutely sure is good. Get a new one. They are like $8 at Schucks for a generic one or $15 at Nissan for a genuine one. Despite what magazines may be telling you, a higher pressure cap is not always a good thing. The radiator cap serves as a fuse of sorts. At a set pressure it pops open. Its better that your radiator pops open than blowing your head gasket. I believe that the RB20 uses the same cap as the stock KA. If you want a slightly higher rating, just go with the Z32 TT cap.

Are your coolant paths flowing properly?

Many of these engines have been sitting for a long time and coolant does some ugly things over time, especially when the previous owners used 100% water or an improper mix of red and green coolant. If when you are working on the system you notice clumps of leaves or rust flakes or things like that you should probably flush your coolant. Just take it to a shop and can get there or buy a bottle of coolant flush and follow the directions on the back. Some of the Australian guys claim that the RB engines can have problems with coolant getting clogged in the water jackets around the pistons. This can usually be solved by a good coolant flush.

Are you using the ideal coolant?

This isn’t usually going to fix problems, but it can help buy you some extra room for error. With any engine, you are going to want to use the best you can afford. I use a mix of Honda OEM coolant. It is blue in color and there is some research that it is superior to most other things out there. It costs about $15 per gallon of 50/50mix. I have found that when going to a Honda dealership, don’t make eye contact and don’t say why or what you need the coolant for. Just get in and get out. I take that gallon of Honda coolant and add one bottle of water wetter and then top off with distilled water (ignore the BS on the coolant about not adding water). Most grocery stores have this on stock. Distilled water has better thermal properties than tap water and causes less damage over time because it is free of contaminants.

Here is a copy of an internal letter at Honda a while back bragging about how good it is. Basically it is the best coolant for use on aluminum such as aluminum engines or nice radiators as it does not clot over time like most coolants.

Because I was unable to use the easily installed Nissport adapter I got a HKS fan controller. It splices into the factory ECU harness and tells you the temperature the ECU is reading which is very accurate. The problem with the stock cluster gauge is not that the sender is inaccurate. It is that the gauge itself is inaccurate. Most people don’t want to see the needle move while driving because they would think something is wrong. Nissan fixed this by using a 3 position gauge in the cluster. You have:
-Cold
-Normal (really wide range of temps)
-Death (when it climbs over the halfway point you are already way too hot and need to pull over now!)

When you see the car starting to overheat on the gauge, you are seeing it too late and damage could be going on already.

The end (Finally)

If after reading and trying all of these things you still have problems it might be worth your time to take it to a shop. If you need advice on the forums make sure you are clear and specific. When does it overheat?
-At idle?
-On the freeway?
-All the time?

Submitted by: Cpt_Impossible

Join the discussion! Here is the thread that inspired this article:

RB20 overheating problems