Overheating issue

[AARONM3]

I bought an Eunos 1.6 a few months back and on my first long motorway journey I noticed the temp creep up after sustained driving a motorway speeds. Easing off the throttle and bringing the revs and speed down to about 60-65mph seemed to bring the temp back down in a very short space of time and in traffic and around town I have no heat issues.

I noticed a small split near the top of the rad which weeped a little once the engine was warmed fully so I replaced the rad (new one- MX5Parts) but the problem persists.

I'm thing water pump next? Any thoughts / ideas / suggestions from folks more learned in the ways of the MX5 than I?

Additional info that may be pertinent- I have aircon but it doesn't work, is the aircon system (aircon rad?) blocking the airflow at higher speeds, should it be doing something on the cooling side? The number plate is on a plinth as per standard and isn't obstructing the front air dam which is completely open and free of mesh/grill.

Oh, and for a bonus point I changed the spark plugs today- they looked fine upon removal but I noticed a small amount of oil on the end of the socket when I removed them. Is that normal or does the VC gasket need replacing?

[ALawson]

Have you drained the cooling system and flushed it?

[I Am Milk]

I guess as he changed the radiator he would have had to have changed the coolant and no need to flush the system as the rad is new.

What sort of condition is your radiator cap in? Did you properly bleed your cooling system when you refilled it?

[AARONM3]

Did a drain and flush and bled as part of the fitting the new rad but I'm not the world's most proficient home mechanic so I'm not ruling out user error although I followed the manual to the letter. I have a tame professional so perhaps I'll get him to take a look a give me a few pointers.

Cheers

[e11nos]

Change the thermostat.

http://www.mx5parts.co.uk/product_info.php/product...

10 minutes work - your old one will have gummed up and is sticking.

[Quick silver]

AARONM3 said:

Additional info that may be pertinent- I have aircon but it doesn't work, is the aircon system (aircon rad?) blocking the airflow at higher speeds, should it be doing something on the cooling side? The number plate is on a plinth as per standard and isn't obstructing the front air dam which is completely open and free of mesh/grill.

Re; The aircon - when the coolant level has lost too much presure, the pump will not engage & so gives the impression that the system is in some way faulty. Very often all that is required is a simple recharge, also there are valve adaptors available for £5 ish that convert from Japanese to the larger EU fittings.

Many aircon service centres will want to charge a premium for overhauling the aircon system when a recharge is all that is required!

[I Am Milk]

How did you get on Aaron?

[franv8]

There can be a few causes to overheating:

One is clogging of the small bypass hose (normally in the thermostat housing where the small outlet hole to the hose is).

Another I had was weeping water pump, loss was so small that it didn't lose a lot and didn't leave a puddle, but was enough to pull air into the system on cooling and cause airlocking. It's given away by if you remove the cambelt cover, you'll see water staining down the front of the block under the pump (i.e. dry brown stain).

Other issues can of course be a sticking thermostat, blowy head gasket, sender shenanigans (i.e. it isn't really overheating), not bleeding it properly (run it up to temp from cold with the rad cap off, and keep the rad topped up as you do it, once it gets to temp and the top rad hose get's nice and hot replace the cap, top up the level in the expansion tank and job done).

Don't rely on the level in the expansion tank, it's not part of the pressurised system and it is possible to have this look fine when you've a half empty rad. And (boring mode on) - DO NOT REMOVE THE RAD CAP FROM A WARM?HOT ENGINE (boring mode off) - it does go everywhere. (You probably know this)

Good luck with the fix.

Francis