Are B-series rad caps a touch larger than D-series?

I know the inlet and outlet ports are a touch larger.

The reason I ask is the aluminum aftermarket radiator I put into my car takes a slightly larger cap than the stock d-series cap.

I would like to replace the thing but I am not sure how I can go about deciphering what car has the proper size and pressure rating.

The d-series is a 1.1 rating while the cap I have is a 1.3. My problem is the bottom hose is staying pressurized even once the engine is cold so it gushes out on me when I pop the cold cap. As well as the reservoir isn't appearing to feed or take coolant from the system. I suspect a faulty high pressure cap and the stock cap I bought doesn't fit, of course.

Or is there a reference table for radiator caps, sizes and pressures that I could use?

 

They are the same even though the ratings may vary.

 

Thanks

It appears the earlier civics had a slightly larger cap than the D and B series caps.

Seems there is two type caps depending on the radiator. Type A and Type B both at 1.1 bar (16 PSI). I ordered a cap that I hope is the slightly larger Type A cap that I believe should fit my after market radiator but is 1.1 bar instead of the 1.3 that is currently on there.

Spent a lot of time searching last night trying to wrap my head around this.

 

I think it's just the outer housing that looks of a different size. I have used and bought new Genuine Honda radiator caps for Integras and Civics and they are the same...pretty much.

 

There's 2 sizes of caps, one for aftermarket, but it also fits early hondas, and then the late model cap which fits all OEM radiators.

You can tell by looking at the little wings on the side.

The cap for aftermarket radiators has rounded tabs, the one for OEM radiators has square tabs.

 

Thanks 2LEM1, that's what I was finding too.

And for future searchers, stock pressure is 1.1 bar (1.1 kg/cm^2) for 92-95 civics. So for most aluminum radiators, if you want to stick to stock specifications you will be looking for Type A cap with 1.1 bar (1.1 kg/cm^2).

In my research, people up to the 1.3 bar (18.9 PSI) to raise the boiling point at the cost of added strain on all seals and components of the cooling system.

Cheers

Hey 2LEM1, do you know what year Honda's had the Type A as stock caps?

 

Just off the top of my head I believe it was older Integras, like Pre-DA, and actually I think NSXs use that cap as well. IDK, it's been so long, I don't really remember.

 

Nope, I'm wrong, it is DA Integras.


88-91 Civic/CRX
90-93 Integra
92-01 Prelude
91-05 NSX

 

Awesome! Thank you. I was not having very much luck finding that bit of info. Probably searching wrong.

If the one I ordered doesn't work, I now know what OEM equivalent cap to ask for. I honestly don't see a need to increase cooling system pressure beyond OEM spec for a stock Z6 setup on an aluminum dual core radiator.

The only thing it does, besides tests all the rubber in the system daily is soak my hand/wrist and/or rag every time I pop my radiator cap.