Miata Q - any tips for removing the heater hoses?

Specifically the one that connects at the back of the head?

I'm doing a cooling system overhaul and so far this is the one hose that won't budge. The other ones came off OK, it's just this one that is being awkward.

Oh, and before I make an ass of myself on the phone tomorrow morning - top radiator hoses normally don't need cutting to length, do they?

And the last question: the electrical connector next to said radiator hose (below the cam angle sensor)is the temp sensor for the ECU, correct? Just wondering because that looks like it wants de-oiling.

The best thing to do is cut those hoses off and replace them. Not only are they a bear to get off, the soft brass or aluminum (depending on year) fittings for the heater core are really easy to damage.

Depending on the upper hose, it might need cutting. Some aftermarket ones are just a bit off. Heck, I've had to cut some factory ones to improve the fit a bit.

Both the ECU and the gauge water temp sensors are on the back of the head. On an NA, the single wire sensor is the gauge and the dual wire is the ECU. On an NB, they're integrated into a single unit with three wires.

I've got the hoses off the heater core (cut them off), I just need to the the one that connects at the back off the head of its connection at the engine. I'll see if I can get a knife back there.

BTW, the top hose I have is about twice the length compared to the one that I took off, so we're not talking about cutting off a little here.

Time to go back into the garage then.

Oh, does anybody have a good idea on how to get the crud/deposits out of the expansion tank? Dishwasher won't work as we don't have one.

I used soap and hot water with some pebbles inside the tank. Shake it to dislodge the crap, rinse and repeat. It didn't get everything out but it is much better than it was.

I'll try that. I'm also thinking about getting a bottle brush, let the tank sit with some CLR+water in it and then give it a good brushing.

That would probably work better.

It did, actually. Ended up soaking the worst deposits overnight and I got the majority of them out. Not everything, but it's a big improvement over having the bottom 2/3rds of the tank covered in some sort of blackish sludge.

Keith wrote: The best thing to do is cut those hoses off and replace them. Not only are they a bear to get off, the soft brass or aluminum (depending on year) fittings for the heater core are really easy to damage. Depending on the upper hose, it might need cutting. Some aftermarket ones are just a bit off. Heck, I've had to cut some factory ones to improve the fit a bit. Both the ECU and the gauge water temp sensors are on the back of the head. On an NA, the single wire sensor is the gauge and the dual wire is the ECU. On an NB, they're integrated into a single unit with three wires.

If I can get away with just asking here, do you know off hand which wires on the NB go to the ECU and which goes to gauge? Or can you just point to online wiring diagram? Thanks, and sorry to get off topic.

Hmmm...so that is what that little plug that I left dangling goes to...

I assume that if I use the 3-wire sensor and plug I can splice in the 3 wires from the NA harness and have a working temp gauge?

I'll have to check out my wiring diagrams tomorrow.

BoxheadTim wrote: Oh, does anybody have a good idea on how to get the crud/deposits out of the expansion tank? Dishwasher won't work as we don't have one.

I just bought a new one, it wasn't all that expensive.

Can you get a hook tool in there?

I barely managed to get my hand in there, and I've got fairly small hands. Similar problem getting a knife in there but I got the hose to break free in the end and got it out.

codrus wrote:

BoxheadTim wrote: Oh, does anybody have a good idea on how to get the crud/deposits out of the expansion tank? Dishwasher won't work as we don't have one.

I just bought a new one, it wasn't all that expensive.

Yeah, but I managed to save myself around $60 with some scrubbing . The tank wasn't damaged, just dirty...

EvanB wrote: Hmmm...so that is what that little plug that I left dangling goes to... I assume that if I use the 3-wire sensor and plug I can splice in the 3 wires from the NA harness and have a working temp gauge? I'll have to check out my wiring diagrams tomorrow.

Let me know how that works out. I'm interested in doing the same.

Looking at my NB wiring diagram, there only appears to be 2 wires on the coolant temp sensor? Black/red and red/blue. Would that mean that the third one that is a different color goes to the gauge?

The 90 wiring diagram shows the coolant temp sensor with wire colors Blue-white and Black-Lt green.

Electrically, the NB sensor is really two in one. So the wiring diagram shows it as two sensors, but they share a common housing. I don't have the wire colors handy, sorry.

On my NB engine swap, I just put the NA sensors into the NB head. There's a fitting for the second sensor that's just plugged with a bolt. The only reason I did that was because we needed the NB sensor for the car the engine came from, otherwise I probably would have wired it in.

EvanB wrote: Looking at my NB wiring diagram, there only appears to be 2 wires on the coolant temp sensor? Black/red and red/blue. Would that mean that the third one that is a different color goes to the gauge? The 90 wiring diagram shows the coolant temp sensor with wire colors Blue-white and Black-Lt green.

The wiring diagram for the gauges is showing a violet/white wire corresponding to that third wire off the sensor.

I'm as yet unsure about which of the other two wires corresponds to which in the NA harness.

Keith wrote: On my NB engine swap, I just put the NA sensors into the NB head. There's a fitting for the second sensor that's just plugged with a bolt. The only reason I did that was because we needed the NB sensor for the car the engine came from, otherwise I probably would have wired it in.

In that case I will just put the NA sensor in. I didn't notice the bolt before.

EvanB wrote:

Keith wrote: On my NB engine swap, I just put the NA sensors into the NB head. There's a fitting for the second sensor that's just plugged with a bolt. The only reason I did that was because we needed the NB sensor for the car the engine came from, otherwise I probably would have wired it in.

In that case I will just put the NA sensor in. I didn't notice the bolt before.

For whatever it's worth, it looks like splicing the R/L wire from the NB with the Blu/W from the NA, and the B/R with the B/LtG gets you where you're going.

I'll be trying it that way, since the sensor of the 1.6 got broken.

Where is the fitting for the second sensor? All I saw was a 17mm bolt and that hole was too big.

It might have an allen head on it, I forget the exact details. It's the one that has coolant behind it

The 17mm bolt had coolant behind it too