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Radiator Express. Thread Pitch for Coolant Level Sensor?
Long shot here. Anyone used a Radiator Express radiator for a first gen RX7? SKU 221255. If so, do you know the diameter and thread pitch for the coolant level sensor port, or if you purchased a sensor for this radiator do you have the specs or a link? Tried phone, online chat and text help with Radiator Express and no one has the answer. The male plastic plug that comes in the hole is a very loose fit so not a good guide. I am assuming its metric, but a M14 tap will not start and dont want to force it and a M12 is too loose. Would go buy a bunch of bolts and see what fits, but metric are slim pickings over 12mm.
And... If I try to run the engine with the plastic port plug in place in the level sensor port (the plug has a rubber O ring so seems more than protective) will it melt!
I have a very similar radiator in my car that I purchased from eBay - looks nearly identical to the one you linked and has the same plastic plug (like a wing nut, but a bolt). For what it's worth, the plastic plug will not melt, so I wouldn't be worried about that. It's not the strongest though, and the o-ring that was included with mine did start to leak (you could just barely hear it hissing with the hood open after the car shut down). Replacing the o-ring solved my issues, but I've heard from a number of people that those plastic plugs can break pretty easily, particularly if over tightened.
If I recall correctly the thread is actually an imperial thread, but it's been a while since I checked. Unfortunately I'm not home and will not be for a week or so, but I might be able to check it again once I return if no one else has already helped you by then.
I'd take the plastic plug to a hardware store and find something that matches. Many stores (like Ace hardware) have studs and nuts mounted on a board so you can find the right threads. Didn't your car have a level sensor?
Took the plastic plug to the local hardware. They do have a test board of female threads, and it threaded in to a M14 x 1.5 hole. However when I test the female hole in the radiator my M14 x 1.5 tap will not start, and when I thread the plastic plug into my M14 x 1.5 female tap it feels very loose. This has got me paranoid and thinking maybe its imperial and not metric? However the pitch seems to be 1.5mm which would make it a 18 threads per inch in imperial which is pretty rare. Argh!
I do have the original sensor but it is a smaller diameter thread than the (supposedly) OEM matching radiator that arrived.
Sorry if this double post, but last one did not seem to take.
Tried the hardware store thread board. Closest seemed to be M14 x 1.5. However they dont have any male bolts to purchase in that spec, and when I try a M14 x 1.5 tap it will not start. Paranoid that it may be imperial, but pitch would be 18 tpi which I believe is a weird size? I do have the original sensor, but diameter of the threads is much smaller than the port in the new radiator.
Male taps are usually a hair bigger than the bolt you're tapping for. IE: a 1/4-20 tap usually won't thread into a 1/4-20 nut, even though the bolt does easilly. But on a $280 part I would be paranoid too! I wouldn't trust a plastic plug not to get brittle over time.
Maxwedge has a good point about taps not always fitting into female threads. It depends on the quality and tolerance of your tap set, so that may very well be the case here.
You know, I just had a flashback here. If I recall correctly that bung (at least on my radiator) is NPT. I figured that out when I noticed that the threads got tighter the further in I threaded something, can't remember what it was. That would also add up to why it might by 18TPI - 1/4" and 3/8" NPT are both 18TPI. Food for thought.
Edit: I should mention that the included plastic plug is indeed straight thread, they just cobbled the two together with an o-ring to make it "work". Thinking back, when I was replacing the o-ring I think I tried threading the plug in without it and discovered that the plug wouldn't actually thread all the way in because the threads were tapering down. That'd be another quick way to check it.
Last edited by Benjamin4456; 03-23-22 at 02:25 PM.
Good to know I can run it with the plastic plug for now. Have a M14x1.5 metal plug on the way to see if that is indeed the spec for the female thread. Will drill and tap for original sensor if the plug fits.
and just turned the engine over (fuel pump fuse pulled) to move the fluids around and by God it actually turned! Will actually try for a real start tonight.... it’s my kids car and he gets first key turn. Fingers crossed.
Took the plastic plug to the local hardware. They do have a test board of female threads, and it threaded in to a M14 x 1.5 hole. However when I test the female hole in the radiator my M14 x 1.5 tap will not start, and when I thread the plastic plug into my M14 x 1.5 female tap it feels very loose. This has got me paranoid and thinking maybe its imperial and not metric? However the pitch seems to be 1.5mm which would make it a 18 threads per inch in imperial which is pretty rare. Argh!
I do have the original sensor but it is a smaller diameter thread than the (supposedly) OEM matching radiator that arrived.
I got the same problem......my radiator has the plastic plug and the low coolant level sensor is smaller that the hole for the plug.....I either need to find an aluminum plug or a low level coolant sensor that fits.....🤷♂️
The M14 x 1.5 plug just arrived. And does not fit. Too large a diameter, although the thread pitch does look darned close to the plastic plug that the radiator came with. Going to try some NPT fittings next. The jury is out on if the female thread has a taper, took a rotary caliper to it but if it does taper its not my much. Will let you know what I find.
Dug some more into what Benjamin4456 was thinking... that the female threads in the radiator are NPT. Sounds possible as a 1/4" NPT male thread has a 13.7mm external diameter and 18 threads per inch is darned close to 1.5mm thread pitch. Will try that next. Anything to avoid facing the nagging possibility that I crushed a needle bearing when I pulled the pulley off the main shaft making room for the water pump fix. And I thought rebuilding the engine was going to be the hard part.
OK, found a 1/4" NPT from another project I am working on. Its a 18TPI and thread pitch does seem to match the plastic plug that came with the radiator. Diameter at the start (narrow) end of the threads is 13.4mm. Thought it was a winner, but the fitting binds hard after one turn in to the radiator. RadiatorExpress chat and phone help dont have an answer. Have submitted for a return on their website, with the question on the thread pitch in the notes. Lets see if that gets us an answer.
03-23-22, 01:09 PM
