MX5 Overheated - HG?

Badgerpoo

Badgerpoo

Badgerpoo

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Just bought an MX-5 for my girlfriends mum, unfortunately on the way home it decided to desintegrate the waterpump/alternator belt and proceed to horribly overheat. Ugh.

Not sure how bad it is as yet, as soon as i noticed it was hot I pulled over and got towed home, but I could easily have been driving 10 minutes with no coolant flowing. The nice RAC man replaced the belt, but unfortunately there is a leak in the hose circled below:

coolingprob2.JPG


coolingprob3.JPG


Two questions:

How easy is it to replace that part of the piping, it seems to be a metal part, but could be the surrounding rubber bit. Will need to wait for daylight to check for sure.

How likely is the HG to have been blown, and what is the best way to tell?

I promise some shiny piccies tomorrow if I get some help!
 
Its rare for the HG to go in the MX, and since the engine is designed to run under loads more load and hence produce more heat than stock fingers crossed you should be ok.

That looks like the pipe out of the waterpump, its a metal housed pump with a rubber hose that runs down the side of the block into another metal pipe iirc, its a weakspot since it gets hot off the block / manifold.

Easy enough to change but you might need to take the manifold heatshield off.
 
Here is a picture of the affected part (taken using a mirror). You can see where corrosion has worn a hole in the metal bit. Is this part replaceable? If so, how do I do it?

coolingprob4.JPG
 
That looks like it's been repaired before with that lump of braze on the bend.

That pipe looks to be for the heater circuit, and unfortunately it's cast into an alloy component so you can't easily replace just the steel pipe. I guess the alloy part is the water pump or thermostat housing (hard to tell from the pics you posted), replacing the entire part is likely to be the only satisfactory and permanent fix.
 
The affected part is circled below:

coolingprob5.JPG


There is a pipe running down from the thermostat housing into this metal pipe, which seems to run underneath the exhaust manifold.
 
It should attach to the back of the engine, you need to change the whole pipe if its the one i'm thinking about.

Might be worth doing the coolant re-route mod to stop this going again.
 
I think the pipe in question and the one thats failed runs down the block underneath the manifold and to the back of the engine, the pipe gets silly hot, since this block was originally from the 323 turbo and was designed for Forced Induction the cooling of cylinder 4 (i think it is) doesn't work so well.

The reroute takes the pipe out from beind the manifold and above it iirc.

Works very well, mainly used for FI applications but if the whole pipe is shot you might as well change it if you can.

(*I think thats the pipe in question, its hard to see from the pictures, it should be a long tube about the same size as normal copper heating tube for the house.)
 
that very pipe leaks on my white mx5, albeit from the rubber bit not the metal bit.. hasnt lead to any over heating ever, i will change it when i cba
 
Well, what I've done is hacksaw off the elbow bit leaving just the straight bit of pipe, and connected a new pipe from that to the stat. Looks good!

Now I need to refill the coolant and get it flowing, trouble is I've never done that before so am not sure what to do. So far I've refilled the radiator and let it idle for a few minutes, but the level didn't change and it doesnt seem like anything is flowing at all?

edit: and how do I find/eliminate airlocks? I'm sure there are some in there by now...
 
If you look at the water piping, you will see nipples, you need to unscrew these in order to get the air out, think you start at the highest first.

You should really keep the revs at a constant 2k for 5mins or so to flush the coolant though and get rid of all airlocks.
 
Ok, it seems to be fine! Gets up to temperature and stays there. Thank God.

New problem though: Having run fine for about 30 minutes of enthusiastic testing, now its running rough. Under throttle it'll seem to misfire and bog down, and it wont idle smoothly. Browsing around seems to point at the problem either being the Throttle Position Sensor or HT Leads. I tried reseating the sensor plug, and noticed that it runs better (but not great) with the sensor fully removed. The problem remains when i plug the sensor back in. I'm completely stumped now, what to try?
 
Mine did this when the Lambda O2 sensor was nailed, you should have a connector on the front of the block at the top, blue / white / grey / black wire if its a 4 pin heated one.

The sensor is in the manifold just under the heatshield lower edge.

Check the wires / connector out.
 
I dont quite understand where you are referring to.. Where abouts is that sensor when you are looking down on the engine from the front?
 
The physical location of the sensor is in the downpipe from the manifold, its a stuck out barrel from the exhaust, just below the bottom edge of the manifold heatshield.

Follow the wires back, they trail to the front of the engine, you should see a connector block, check this out as well.
 
I see it! It's at the back of the manifold and the wires trail around the back. Im fairly certain its something I've knocked while removing/refitting the intake pipe, or while fixing the coolant pipe. I can't fathom what it is though unfortunatley, so I'm just going to give up and have a garage look at it.

Here are some photos anyway:

mx51.JPG


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mx53.JPG
 
Turns out the HT leads had melted onto the spark plugs and were arcing onto the cam cover, replaced HT leads and plugs and all is well! It must've been damn hot, I'm amazed the HG withstood it all.
 
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