Overheating slowly

Cus · Postby **Cus** » Thu Dec 10, 2015 9:02 pm

Dear Diary,

The weather is much less insane today, but took myself on the bendigo -> lockwood -> maldon -> castlmaine -> bendigo loop expecting the car to behave itself.

The needle was rock solid until I got on the freeway home going up big hill (surprisingly, it's a big hill) where the options to get up it are either 'full throttle' or 'very slowly' - naturally, I opted for the full throttle option, but still crest the hill only doing about 95 clicks in 5th. By the top of the hill the needle was vertical, and by the other side of the hill, it was back to it's place.

It behaved itself until I got into town and decided to see if it was rev/load related (I usually putt around in the highest gear possible, so unless I'm freeway driving I'm rarely over 3000 RPM)

60 clicks in 2nd is about 4100 RPM. Sounds beasty. Cus approves. But. There was a fair bit of traffic, so watching the temp needle wasn't an option due to people being their usual selves on the road. At the next set of lights I looked again and we were well over half. I went back to normal driving, and the temp went back to normal.

So, my idiocy wasn't the issue. I should be happier about that... lol

I read through that page tbro, looks like it was "faulty radiator" in the end?

In other news, the price of the 42mm radiators on ebay randomly went up $20. ALL of the radiators, from ALL of the sellers. I suspect there's a conspiracy afoot! *tinfoil hat*

smy0003 · Postby **smy0003** » Fri Dec 11, 2015 11:49 am

So you didn't put it in this way?

Cus · Postby **Cus** » Fri Dec 11, 2015 12:08 pm

I did this time!

gslender · Postby **gslender** » Fri Dec 11, 2015 12:12 pm

Don't over look rad cap

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Nevyn72 · Postby **Nevyn72** » Fri Dec 11, 2015 12:27 pm

gslender wrote:Don't over look rad cap

I think even Cus would struggle to put that on backwards! :shock:

Cus · Postby **Cus** » Fri Dec 11, 2015 1:02 pm

Nevyn72 wrote:
gslender wrote:Don't over look rad cap

I think even Cus would struggle to put that on backwards!

Challenge Accepted!! :lol:

But in all seriousness; the theory of a rad cap is (as I understand it) when the pressure builds because the coolant is hot the spring in the cap pushes back, and the coolant can flow into the overflow bottle via the little tube that connects to the neck of the radiator, then vacuum sucks it back as the coolant cools down again.

If that's the case, I think it's working as intended; the overflow bottle is just over "low" when cold and usually just below "full" when it's up to temp.

hks_kansei · Postby **hks_kansei** » Fri Dec 11, 2015 2:05 pm

Cus wrote:But in all seriousness; the theory of a rad cap is (as I understand it) when the pressure builds because the coolant is hot the spring in the cap pushes back, and the coolant can flow into the overflow bottle via the little tube that connects to the neck of the radiator, then vacuum sucks it back as the coolant cools down again.
.

Yes, however increasing pressure increases the boiling point of water/coolant (which is why opening the cap when hot is so dramatic, pressure is released suddenly and at the same time pretty much all the coolant wants to instantly boil and expand, which means it shoots a boiling jet of skin grafts out the cap)

Anyway, if the cap is opening at too low pressure it can cause issues. New cap is like $10 so may as well stick one on.
If you want, I have seen at some shops radiator caps with a temp gauge built into them, might be an idea so you can see how how the coolant actually is compared to the gauge in the car.

project.r.racing · Postby **project.r.racing** » Fri Dec 11, 2015 3:15 pm

Have you tried the driving-with-the-heater-on-test when it is overheating? Could rule out a few things like head gasket. It costs nothing except for a few litres of fuel and a few litres of sweat, (considering the heat at the moment).

Cus · Postby **Cus** » Fri Dec 11, 2015 4:38 pm

I do like the idea of a rad cap that has a temp gauge with actual numbers on it!

Today in Bendigo it's cold and drizzling sideways. I did take it for a squirt and it's being a good little car, so it's definitely related to the car's ability to shed heat into the atmosphere.

Monday is when the weather will be back to the usual summer programming, I'll try the heater method then. What's the theory behind the heater method in relation to the head gasket? I know having the heater on and the cabin fan on full should take some heat out of the cooling system, but aside from that, I've no idea what to look for.

New radiator will be here around Wednesday, so I'll know for certain shortly after that if it is the radiator's fault or not.

hks_kansei · Postby **hks_kansei** » Fri Dec 11, 2015 5:02 pm

Cus wrote:I do like the idea of a rad cap that has a temp gauge with actual numbers on it!

the look like this:

http://shop.advanceautoparts.com/p/mr.- ... /6900022-P

That's not the ones i've seen in the shop, but it's along the same lines.
If you do get one make sure to check it clears the bonnet, the caps are a bit thicker on top than a normal cap, and mx5s look to be pretty tight to the bonnet in that area

Mr Morlock · Postby **Mr Morlock** » Fri Dec 11, 2015 8:04 pm

Magna is of course right that the OEM radiator is perfectly adequate for a road going MX5 which should operate without problem even in heat wave conditions. An OEM rad with last probably +10 years. Personally I reckon OEM is the better radiator as it is actually designed and tested for the car. However I am also assured by the local radiator repairer who is very busy says that flushing is a waste of time as it will not remove built up deposits.

Cus · Postby **Cus** » Fri Dec 11, 2015 10:59 pm

hks_kansei wrote:If you do get one make sure to check it clears the bonnet, the caps are a bit thicker on top than a normal cap

My current cap is 9mm from the bottom of the lock tabs to the top of the cap.
An empty 40mm carboard box did get squished by about 10mm while on top of the cap
My wallet is 21mm thick (I was running out of 'soft' things to test with) and I can close the bonnet with my wallet on top of the rad cap, and it does not feel like I'm squashing something when I close the bonnet, so a 30mm cap height should be safe (tab-to-top), 40mm is probably pushing it.

Armed with that information I toddled into SCA and was told they haven't stocked them for years because nobody ever bought them. Oh well. I'll put in more effort to find one that fits if I put the new rad in and decide it's still something I want to know.

Mr Morlock wrote:An OEM rad with last probably +10 years.

As far as I'm aware it's the original unit, so it could be over 25 years old by now!

Mr Morlock · Postby **Mr Morlock** » Sat Dec 12, 2015 12:47 pm

At one stage it was possible to buy an electric carving knife with an built in light for candlelit dinners but apparently it did not catch on.

Cus · Postby **Cus** » Sat Dec 12, 2015 2:50 pm

Avoiding the obvious pun about "catching on"; Mum used to have an electric carving knife - great to cut up a leg of lamb for 7 people - but putting a small flame thrower on the end isn't going to make it romantic.

"Here honey, let me light your candle"
*fwoof* *romantic candlelight*
"Now let me slice you some of this delicious meat"
*BNNNAAAAAAWWWWWWWWWRRRRRRRRRRRRR!!*

...and then the date ends with the other person trying to back out of the house without breaking eye contact while simultaneously trying to text their location to a friend out of fear they're about to be locked in a well and made to put the lotion on their skin.... :lol:

SuperMazdaKart · Postby **SuperMazdaKart** » Sun Dec 13, 2015 9:33 am

hks_kansei wrote:
Cus wrote:I do like the idea of a rad cap that has a temp gauge with actual numbers on it!

the look like this:

http://shop.advanceautoparts.com/p/mr.- ... /6900022-P

That's not the ones i've seen in the shop, but it's along the same lines.
If you do get one make sure to check it clears the bonnet, the caps are a bit thicker on top than a normal cap, and mx5s look to be pretty tight to the bonnet in that area

I bought one of those from CPC I think it was sold at SuperCheapAuto. Also used it in the NA6 when I had it. Worked fine but coolant did leak into the gauge area though, maybe got the dud one or maybe they aren't too reliable.