My little car has been driven all through the UK, France and even a bit of Spain, and for the past 6 years it has a tendanciy to overheat while going up hills or extended highway driving in the summer. I’ve replaced rad and filled with 60/40 ratio, timing back to 10*, and new water pump. I’ve also put in a “slam panel” at the top of the rad, but was curious about the bottom.
I’ve read that some people just think these older NA’s just overheat, especially in 35c summers, but I find that hard to believe. But I have to also believe that driving this car with a full trunk, two people and a full tank of gas over the Pyrenees might just be a bit of a strain on a 23 year old car.
My question is…there is a gap below the A/C rad and the under tray of just over an inch where incoming air could be going instead of through the fins of the radiator. Should there be something there to further guide the air through both A/C and cooling rad like the top slam panel?
I don’t know the answer to your question, or the solution to the overheating (sorry!). But, just for reference, I don’t have the undertray or slam panel and I never see the temp gauge shift from the middle even during long sessions on summer trackdays. So I would guess the problem lies elsewhere, unless there is something peculiar about the autos?
At one point or another I’ve done it at least 3 times. The last time was when I had the water pump replaced a couple of years ago. Done at a dealer so hoping they used the right parts. I only drive it 2-3000 miles a year, so assume it’s still fine.
My question was more about should I be trying to channel more air through the mouth of the radiator, and if it was normal to have such a gap between the bottom of the rads and the undertray. Every year I go through all the possibles, but there really is no way to know if I’ve fixed it until I drive up a long steep hill in France in the summer.
You have a 20 odd year old sensor and guage are they accurate what about changing the rear sensor that does the guage and ECU and the front one to make sure the fan is cuting in when required.
Where does the needle on the guage sit at normal and how much higher when you say it overheats.
Have you used a descaler to clean the internals of the system.
Maybe better to take the rad out and put a hose through the system for a while before putting the radiator back on.
Maybe the new radiator has got a bit blocked from old dirt in the system.
Dose the car go through water during say 200 miles of normal running or 200 miles of hot weather running.
Why not try and make a lower slam panel to see if that helps, if not remove it.
The front one switches on and off the fan but you have changed that and you are happy with the fan switching on and off.
The rear one is below the coil packs so you need to disconnect the battery, take out the coil pack nuts, 12mm af and lift it out, be careful with the wires.
The sensor is there to see, it tells the ECU what the temperature is and feeds the temperature guage, cost about £20 but I wonder if it is the problem, I’m going to guess not.
Gut feeling and nothing more is that when you changed the radiator did you descale and flush before putting it in or after.
Just maybe it is partially blocked again.
In saying that the rear sensor is only £20, I’m going to say change that and take it on a long motorway run to see if it overheats as you say it is not using water!!!
Does it overheat on a UK motorway at about 15C to 20C.
If only at high altitude maybe the mixture goes very weak at altitude, the Triumph TR5 guys have similar problems on Alpine Passes due to no altitude compensation on their 1970’s fuel injection.
Sorry can’t help with your question re the gap but doubt that would be your problem anyway. In my experience overheating in the conditions you describe is usually down to a thermostat not opening up as it should or an ineffective radiator. Did you fit a genuine Mazda radiator? Is the coolant nice a clear with a blue tint? If I was buying your car off you right now with this known fault I would do a cooling system overhaul. Take out the rad, flush/descale the engine, fit new radiator, cap and thermostat using all genuine parts. I would also replace any suspect hoses. I would then refill the system with the correct mix of antifreeze and distilled water.
I see your car is an auto. Does an auto use the same rad as a manual?
In your position I suspect you are not inclined to go over stuff you have already done and I can understand that so give the thermostat a miss as it has been replaced several times. That just leaves the radiator. So was it an original Mazda rad? Is it the right type for your car. Did you flush the engine before before you fitted the last rad?
Thanks for all the thoughts. Since you’ve very clearly run through every possibility, I beginning to think it’s the rad. I replaced it with a genuine Mazda rad for an automatic (it is different to a manual), and coolant is clear with blue tint. I bought the car for a specific trip 6 years ago, and it was overheating before we left. This was '09, a very hot summer in the UK, It being a new car to me, I was running around trying to get it all fixed before we left…new rad, thermostat, front sensor…It’s likely that I didn’t fully FULLY flush the system then, so the new rad caught some of the old gunk. That said, last year I flushed/filled/flushed/filled maybe 7 times until all the water was clear as a bell. And if I look down inside the rad cap opening, the fins look very clear, at least the few I can see, but I know that’s not many…
The car is running fine now and always has when the weather is at normal temps, but I’m just trying to cover my bases as about to head to Southern France again. If it happens again this time, it’ll be the last chance this car gets.
Hmm, one other very remote possibility is that the timing is not quite right, either with the valves or the ignition or both.
I have found overheating on a friend’s Cortina once where the distributor advance springs were broken so it was (almost) always fully advanced, but the previous owner had bodged it by retarding the whole distributor so static timing was OK and it would start but normal running was dreadfully retarded; and also on an old Mk1 Cavalier I bought where the timing chain and sprockets were so badly worn the valve timing was almost a whole cam sprocket tooth retarded - the timing chain rattle was awful!
Sorry, should have mentioned that when I had the water pump replaced, they also did the timing belt, both done at a dealer. I wouldn’t normally go there, but it was the only place available at the time and glad I did for such an important job. I assume they would get it right. Was overheating before that anyway.
Using a timing light, I’m spot on 10*, as that seems to be the common sweet spot, unless you go for the 14* tweak. I seem to remember an old school way of checking first piston is TDC by taking the plug out and gently placing a long screwdriver in, and hand cranking to find the TDC point.
Hmmmmm, just double checked my workshop manual (Grainger & Shoemark) and they say automatics should be set at 7-9* BTDC.
Looks like I’ll be adjusting that then, just in case.
Along those lines, I’ve been googling and going square eyed studying the path of the coolant for any other possibilities, could minor blockage in the ISCV cause overheating at altitude or under stress? I dismissed it because my idle is fine.
As your idle is fine I cannot see that being an issue.
The two main cooling systems on a car are the water system that takes heat away from the engine and looses heat in the radiator to the surrounding air.
The other route is via the engine oil and from about 1994 all the cars were fitted with an oil cooler to get the engine oil at a better temperture as at high tempretures it can Rreduce it’s lubrication properties.
I cannot see the lack of an oil cooler on your car putting the tempreture guage higher but you never know.
There appears to be threo options only left to you.
You say you have an automatic car radiator which people believe has a higher duty than a manual car radiator. It may or may not be partially blocked.
There are reports about the early 1.6 engines in some cases overheating under high load and others not overheating heating.
MX5 parts sell a front air guide for these cars and I assume they are a standard fitting is it fitted.
Therefore at the end of the day you have one of two problems or maybe both.
Either your engine is at the edge of the boundry of overheating and in that case it is bad luck and you would need to change the engine for your alpine pass work.
The readiator has got blocked after fitting due to cleaning the water passages when it was in possibly.
In that case the cost of a higher capacity competition radiator is not a lot more than a replacement automatic radiator.
It is still a pain having to buy two radiators in a few years.
Third option is to sell your car and buy an 1.8 that will not be as stressed on the alpine roads.
One last possibility occurs to me is that some of the thermostats have two valves, which makes the main opening quite small. If you have one of these (intended for better fuel economy in colder climates) then fitting the simpler single valve stat with the bigger opening might make the difference. Here is a pic showing them.