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Hi All, I have searched the forum and found about a bazillion post's re overheating, however nothing that fits my circumstances, (I kind of suck at search tho, so happy if someone points out a similar situation).

OK so the issue is that my stock 1990 NA is overheating, typically when cruising the temp guage sits at around 1130(ish), I noticed however after replacing my stock radiator (it was cracked) with a 45mm polished aluminium jobby from mania, the car ran hotter, thermo fan on all the time etc.

When doing a run down the freeway around 110KPh, it gets hot... moves over to about 1 oclock until I back off... I thought this symptomatic of a blown head gasket so I took it into ASR automotives to take a look.

We discovered a few other things with the engine so we decided to do a complete engine rebuild.

Here is what we did.
Complete tear down, hot wash of block and rehone and replace welsh plugs.
Carbon cleaned all pistons and replaced rings.
Replaced bottom end bearings and polished crank
Re machined the heads and replaced all valve stem seals,
Replaced all gaskets including head, rocker cover the whole she bang
Replaced thermostat and put the whole thing back together... all within factory tolerances

Its been about a month now ~1000km's I have changed the oil and filter (15-50W Elf synthetic) and just got back from a run to Bathurst... freeway (typically climbing) gets hot about 1 o'clock on the dial...
Going up Bellbird hill....geez in got hot, close to max temp before I coasted down the other side and things dropped to normal again....
Has anyone come across this situation before? I think I have covered all bases except a cracked head... though i would have thought this would have been detected during the remachine... Any help would be much appreciated....

Stu

sound stupid but is your temperature gauge correct,
I had a similar thing twenty years ago and got my cooling system pressure flushed which seemed to make a difference.
Thermostat working, try taking it out and see if it makes a difference, maybe its stuck closed.
Hope one of these suggestions help
Cheers
Dale

thermistat? ive had 3 brand new ones be faulty. that or there might be sludge in the holes where the thermistat goes clogging it up. id check that for a $20 possible fix and for the cash if it hadnet been changed recently id give it a go. i had an issue like that with a sticking thermistat. I might be totally off the mark but hey, worth throwing it out there

Thanks Guys, I guess I can't rule out a faulty thermo out of the box, I did test it and it opened right on temp (standard Mazda)... I am beginning to not trust my temp sender unit.... might give that a shot next...

BTW I have the 42MM Coolpro Radiator in place....surely that thing will keep it cool....

it might be very simple. Who fitted the radiator and refilled the system- the radiator repairer or DIY? If it is the repairer you get them to check. If done yourself- simple job they say but can often go awry- is the system really free of any air? I would doubt the temp guage as being the culprit- it worked ok before - it was not changed but the radiator was. If memory serves the heater has to be in on position for refilling and it can sometimes be quite challenging to ensure no air in the cooling system. An engine repairer will be reticent about a warranty if the owner has replaced the radiator,

Is the water pump actually pumping? Take the thernmostat out and run the motor while looking down the radiator cap hole. Should be a good coolant flow visible there.

Mr Morlock wrote:it might be very simple. Who fitted the radiator and refilled the system- the radiator repairer or DIY? If it is the repairer you get them to check. If done yourself- simple job they say but can often go awry- is the system really free of any air? I would doubt the temp guage as being the culprit- it worked ok before - it was not changed but the radiator was. If memory serves the heater has to be in on position for refilling and it can sometimes be quite challenging to ensure no air in the cooling system. An engine repairer will be reticent about a warranty if the owner has replaced the radiator,

Radiator was part of the rebuild.. replaced and fitted by ASR... Checked and rechecked for air traps so I think that one is ruled out....

Is the undertray fitted?

Yup.. Undertray is fitted.... I did notice a 40mm gap between the base of the radiator and the undertray... I will fill this with some foam tomorrow and test again... I will also rig up the parallel fan for low speed cooling...

back to basics.

check thermostat....( done)
check radiator...(done)
check temp guage
check waterpump
check fans

if that all fails......maybe your engine bock is blocked somewhere

ohh and check that your number plaet isn't blocking the front air intake.

I have the horrors even in replacing coolant Cooling systems seem to have minds of their own. Since you have spent the money including the rad I reckon it would be best to go back to the fitters.The radiator fitters should be able to pinpoint it. A cooked engine is a big risk. I have mounted my number plate in the grille opening and it has never been a prob.

Front no plate can be problematic. But obviously depends on driving conditions. I've dríven NA6/8's up the old road. They started overheating with just a little bit of pushing. My own NA6 can ocasionally complain when chasing another car......but pushing real hard. In seriously hot weather on the freeway I can have issues as well
racetrack I'd almost garratee any NA6 with a standard front intake & no plate fitted in front, to have issues.

Since Stu is having issues, and if he does have a number plate fitted there....I'm suggesting he takes it off....may not be all of the issue but may contribute. We are now chasing the unknown.

Thanks guys, once again a recap on what I have done to my NA6
1) Number plate is up high and out of the way on an MX5 Plus number plate mount
2) Running a polished aluminium 45mm radiator purchased from Mania
3) Engine completely rebuilt, which included a block hot bath and hone, head pressure test and regrind, new OEM thermo, new OEM water pump, new gaskets and seals all round
4) Fan is spinning (albeit not terribly fast is this normal?)
5) When A/C is on and second fan kicks in things cool down when in traffic
6) Gets hot when climbing gets hot when at freeway speeds...

I am beginning to believe that the temp sender unit is cactus... but it is in a beyatch of a place to get at....

front nbr plate at least on NB's is only a prob if the cooling system is below par. You get plenty of air thru the "mouth". My bet is the car is showing hot because it is hot Get it checked by cooling specialists- one should not assume that because it is a new radiator it cannot have a prob.

Stu King wrote:.........
4) Fan is spinning (albeit not terribly fast is this normal?)
5) When A/C is on and second fan kicks in things cool down when in traffic
6) Gets hot when climbing gets hot when at freeway speeds...

I am beginning to believe that the temp sender unit is cactus... but it is in a beyatch of a place to get at....

Take a closer look at the "normal" fan - maybe it's dodgy - especially if things improve when the A/C is on and both fans are going. Maybe you could compare your fan operation with another NA6. The fan should come on before the temp goes above half scale. Could be a faulty thermoswitch and/or fan.

More info here: http://www.miata.net/garage/CoolingSystemProblems.html