Overheating under load

Alex Hecht · Postby **Alex Hecht** » Fri Oct 05, 2012 1:33 pm

Hey all, I have a 1990 that only overheats uphill, so far have changed the:- thermostat, removed and flushed the radiator ( that the old owner says he replaced new & original as well as the water pump), have wired the fans to work on ignition, back flushed motor & heater added umpteen chemicals, gave motor external wash, put new top radiator hoses, removed the cover from under the motor bay. Heat is also coming from under the shift.Anyone with any ideas or should I slot a new motor in? HELP!!! She runs fine on flat, even flat out indefinitely.

93_Clubman · Postby **93_Clubman** » Fri Oct 05, 2012 3:31 pm

So overheating under load - have you checked the timing? Factory is 10 degrees BTDC, although some advance it to 14. Any mods?

For that matter have you baseline serviced (major service) the vehicle, or has it been done recently that you have proof of?

bruce · Postby **bruce** » Fri Oct 05, 2012 5:40 pm

Put the plastic tray under the engine back on. It helps air to flow through the bay and exit properly.

manga_blue · Postby **manga_blue** » Fri Oct 05, 2012 8:15 pm

Alex Hecht wrote:Heat is also coming from under the shift.Anyone with any ideas or should I slot a new motor in? HELP!!! She runs fine on flat, even flat out indefinitely.

That sounds like the upper gearshift lever boot is stuffed. Common problem. It isolates hot air blowing across the drivetrain from the cabin. The exhaust headers get close to red hot on a long full throttle climb, so there's a helluva lot of hot air blowing off them.

Take off the centre console and check the large rubber boot for cracks and holes. While you're at it check out the lower boot on the gearbox extension housing itself. They usually die at about the same time.
http://www.miata.net/garage/shiftboot.html

Mr Morlock · Postby **Mr Morlock** » Sat Oct 06, 2012 12:36 pm

I would follow Manga's and 93's advice. However your idea of a fix sounds a bit crazy- a new motor is not the answer- a new motor still has a cooling system attached to it. Is it really even overheating- how do you know- is it boiling etc? If the radiator was not replaced by you it might still be worth getting it checked - are you doing the work or getting it checked by mechanics.

Postby **Okibi** » Sun Oct 07, 2012 12:09 am

How can you tell she's overheating?

Coolant boiling?
Temp gauge rising?
Both?

Could be as simple as a stuffed radiator cap, why not get the cap and cooling system pressure tested?

vrmmmpshhh · Postby **vrmmmpshhh** » Sun Oct 07, 2012 1:32 pm

dont worry about the heat from the gearstick area. its normal for the rubber boots to crack. I have dríven with everything around the gear shift removed and you'd be surprised with the amount of crap that makes its way up there.

2mins_2_win_it · Postby **2mins_2_win_it** » Mon Nov 26, 2012 10:18 pm

I noticed the same issue on the weekend, while on the freeway going up hill the temp gauge shot up so I jumped off the free way and on a level road the temp dropped almost instantaneously...half thinking it might be an issue with the gauge as I then went up a mountain bout 20mins later and there was no issue

Will still get it looked at and possibly get an alloy radiator put in...I have only had the car 2 weeks so this is all new to me

Postby **Okibi** » Mon Nov 26, 2012 10:44 pm

Fingers crossed it isn't anything too bad, were the radiator fans coming on?

Nige · Postby **Nige** » Thu Jan 14, 2016 5:54 pm

Did you find the cause of this? Mine is doing the same thing (well, has done it twice now). New timing belt, water pump, thermostat, hoses and coolant in March last year.

JBT · Postby **JBT** » Thu Jan 14, 2016 10:49 pm

Suggest a re-post of your question under "Engines etc......" This thread is 4 years old.
Also suggest the first check should be a pressure test to establish if there any leaks and then go from there.

smy0003 · Postby **smy0003** » Thu Jan 14, 2016 11:14 pm

viewtopic.php?f=29&t=70465

Nige · Postby **Nige** » Thu Jan 14, 2016 11:51 pm

JBT wrote:Suggest a re-post of your question under "Engines etc......" This thread is 4 years old.
Also suggest the first check should be a pressure test to establish if there any leaks and then go from there.

Will do, just thought I would follow up on this thread to see if the person with the identical problem had solved it, which you would assume so, but then they may have sold the car since. Also, avoids the replies saying to use the search for old threads ;)

Nige · Postby **Nige** » Thu Jan 14, 2016 11:53 pm

smy0003 wrote:http://mx5cartalk.com/forum/viewtopic.php?f=29&t=70465

Saw this, doesn't seem like quite the same thing, but a few things to check nonetheless. Cheers

TTT · Postby **TTT** » Fri Jan 15, 2016 9:16 am

As someone suggested... is it actually overheating?
My NA6 temp gauge had an odd issue...
it would move around... sometimes towards cold, sometimes towards hot.
I replaced usual things and even the temp sender that sits on top of the thermostat housing.
no effect.

Later on I found out that there is another sensor at the back of the motor.
That was the dodgy one.

The sensors only cost about $10 from any auto shop for a TRIDENT branded one or a little more for an OEM one from the likes of Mazda direct or automotive plus / mx5mania.

If you're actually getting boiling coolant then this is of no help, but if you're relying on the factory NA guage, then at least replace the possible cheap culprits before thinking of drastic things like new engine or water pump etc.