Hi all, what would be the cause of a hot top rad hose, and a cold bottom rad hose,
this was after a 15 mile drive, top of engine to hot to touch for more than 3 seconds, dash dial says no overheating present,
am i right in thinking a back flush to the rad is worth doing, the rad cap is ok (tested that), thermostate has been tested to, there are no obstructions on the mesh grill, just wondered if all this is the norm, thanks guys…
As has been asked many times before, is the rad cap a genuine Mazdaone, if not change it first before anything else.
A very efficient radiator!
How cold is the bottom hose? Same as ambient air temp? Slightly warmer than ambient?
Hi polly,
yes it’s a genuine Mazda cap…
Hi Niggle,
The bottom hose is slightly warmer than ambient, when the cap is removed and i squeeze the bottom hose there is water movement showing, only slightly warmer than ambient though on the bottom hose, the carb intake box and enginge top covers were very hot, if this is the normal operating temperature then i shall leave well alone, many thanks.
ps, i will do a water pump test next.
If the engine is not overheating and the heater/blower is blowing warm air into the cabin then this would suggest that the cooling/circulation is probably OK.
It’s an interesting observation though and I will check the temperature of my bottom hose sometime.
You can check for hot/cold spots on your radiator with an infra-red thermometer.
Results of a thermal survey on a healthy mk1 MX5 (including temperatures across the radiator and the top and bottom hoses) are here:
http://www.mx5oc.co.uk/forum/forums/p/10255/57233.aspx
Dull stuff, but a good benchmark for how hot stuff should get when idling from cold until the engine is warm.
Well niggle, today the bottom hose was hot, not as hot as the top but hot, the reason the bottom hose was hot taday is because i checked it whilst the car was static, when i got in yesturday i was using the car ie: after the 15ish mile trip.
I used a digital thermo reader today and all seems good, fan came on about 12 mins after startup, (static) so fingures crossed, could not run the engine with the rad cap off though to see if the pump was showing water movement, kept pumping out of the rad, not sure if that is common on MX5s
By the way Captain M i found it interesting, it pretty much matched mine
cheers 
[:D] thanks, most people find it really dull.
Well i think it’s spot on ,and i have saved it to word,i’m sure this will come in very handy…thank you.
Regards
Ditto.
I didn’t use any of the Captain’s data directly but it did inspire me to dig out my IR thermometer and check that my thermostat was opening/closing at roughly the right temperature, so thanks for that.
Cheers guys, I have a warm fuzzy feeling inside now [:D]
Don’t worry ,it’s just wind