52 replies to this topic

[sdjones121]

The current thermostat is a 71 degree one. It's new, with a new gasket. Think it's worth it going to a hotter one? 

[Captain Mainwaring]

I must admit, I'm confused. A stat is for one purpose only - to aid quick warm up of the engine. Once it's open, it has done it's job - it can't open 110% if the engine starts to overheat. Both 84 and 71C are well below what we think this engine is running at now. Water won't carry more energy the hotter it gets, that's the job of steam (and you don't want any of that stuff) if anything, the hotter water gets, then the specific heat capacity drops a little - water pumps move a volume of water and not a mass.

 

When you give this car a blast, and it gets into the red on the gauge, have you opened the bonnet and taken a look at the rad? Is she boiling over? Do you have access to a thermometer which would be suitable to read the header temperature? Wouldn't be the first time a sender or gauge has been inaccurate or failed. 

 

I'll stick my neck out - I bet you can take that stat out completely and it won't make a bit of difference to the running temp - if it does, then it is faulty. at 71C it will be close to wide open and if it's not, then could be leading to this cooking up.

 

My car is running a carbed 1275 SPi engine with AC and it won't shift above 'N', it does however have two pull through fans, one for the AC and one in addition to the blow through rad fan - the car was originally a Jap car and as such has a tropical fan.

 

I think you'll end up fixing either a tropical fan or an electric pull through on the inner wing. Pop the stat out and see if it helps, if it does, then the stat is faulty. Fitting a "hotter" stat won't help you at all if the existing stat is opening properly.

 

Just re-reading I note you mention an alloy radiator - ask mini spares to confirm heat transfer for this and a copper rad - I bet they won't be able to do so, and moreover, i'll put good money on the fact that the alloy rad is nowhere near as eficient as they would have you believe. Ally is about 50% worse for heat transfer than copper/cupro-nickel on steam heat exchangers....even worse still is stainless.

Edited by Captain Mainwaring, 27 May 2013 - 11:30 PM.

[Ethel]

Removing the stat altogether could cause water circulation issues in the head. Stick it in a pan of water and stick it on the stove if you want to confirm it opens. If it opens by the equivalent of half the radius of its opening it will flow  as well as it can. I don't think any fan will make a difference at 60-70mph. The stat rating won't make any difference to the cooling capabilities, as capt M said, but it may drop the combustion chamber temperature which will effect the running characteristics and consequently how much heat it produces for a specific amount of power. That said, if you can't keep it down to the rated temperature of the stat, you won't be able to see the advantage, if it even exists.

[Captain Mainwaring]

Removing the stat altogether could cause water circulation issues in the head. Stick it in a pan of water and stick it on the stove if you want to confirm it opens. If it opens by the equivalent of half the radius of its opening it will flow  as well as it can. I don't think any fan will make a difference at 60-70mph. The stat rating won't make any difference to the cooling capabilities, as capt M said, but it may drop the combustion chamber temperature which will effect the running characteristics and consequently how much heat it produces for a specific amount of power. That said, if you can't keep it down to the rated temperature of the stat, you won't be able to see the advantage, if it even exists.

Fair point about hotspots in the head. You could always just remove its giblets to create a little bit of back pressure with no cavitation.

 

Interesting observation regarding the fan - i'll stick an anemometer behind it later today and see what we get - I do think that the flow of air through the rad caused by the car's forward motion may not be as much as you think - even at 70 mph. 

[sdjones121]

I was thinking that switching out the thermostat would not lead much if anywhere, but wanted to see the train of thoughtt. I'm obviously still learning.

I've tested the thermostat (which is brand new) and it's good. It opens in a pot and you can instantly tell when it's opened in-situ since the top radiator hose goes from nothing to piping hot in a very short time.

I too have wondered if any fan will make that big a difference at 70 mph, not knowing the air flow characteristic inside the engine bay while driving.

Has anyone ever seen a comparison on the 11 blade fan vs the tropical fan in terms of CFM? I've looked around and haven't found anything.

It's not boiled over any time I've popped open the bonnet when it's been in the red, no. I know the sender and dash gauge aren't exactly a primary standard, but the readings are at least consistent.

I actually took a few measurements with an IR thermometer when I got back today, but didn't think to do so on the exhaust header. The outside of the upper radiator hose read right around 180f, and the rad cap was about 165f I think. Next time I'll check on the header.

I didn't fit the rad, it came with the car, which is why I know so little about it. Your comment regarding hear transfer is interesting though, and makes me wonder if it may be an issue, compounded by the sharply reduced airflow.

[sdjones121]

Ok, now I'm a bit confused/frustrated/feeling stupid. I just, on a whim, popped open the radiator cap and saw something. As I'd said, I'd topped up the coolant to about 1/2-3/4 above the cores, constant, while it was running. Now when I open the cap, I see the tops of the cores and no standing water, should there not be that same depth of water there now, since I put it at the level while the engine was hot with the thermostat wide open? If so, then I'm obviously losing fluid somewhere. I noticed a small bit of water under the car today after I'd finished the timing. It was about the size of two £2 coins or so. I'd dismissed it, but not sure why I did that. I'm wondering now, if it had a tiny leak at idle, would that leak have been more vigorous at speed. When I have a chance, I'll try to recreate today's timing adjustment and see if I can track down where that fluid may have come from.

 

I have zero visible smoke at any engine speed, so I'm praying it's not a head gasket that's causing fluid loss. Hopefully that small pool of fluid was a "good" omen.

 

UPDATE: Just put a bit more water in, cold engine as it's too late to be running it in the garage to warm up, and it only took 100 ml to get back above the cores. I'd imagine that would suggest that though I may have lost some fluid, it's not been a massive problem. Is it possible the fluid that is gone simply went out the overflow pipe as it got hot?

 

In the mean time, here's a pic I took on today's test drive. Not the normal surroundings for a Mini.

 

 IMG_6470.JPG   105.59K   10 downloads

Edited by sdjones121, 28 May 2013 - 02:53 AM.

[Captain Mainwaring]

I was thinking that switching out the thermostat would not lead much if anywhere, but wanted to see the train of thoughtt. I'm obviously still learning.

I've tested the thermostat (which is brand new) and it's good. It opens in a pot and you can instantly tell when it's opened in-situ since the top radiator hose goes from nothing to piping hot in a very short time.

I too have wondered if any fan will make that big a difference at 70 mph, not knowing the air flow characteristic inside the engine bay while driving.

Has anyone ever seen a comparison on the 11 blade fan vs the tropical fan in terms of CFM? I've looked around and haven't found anything.

It's not boiled over any time I've popped open the bonnet when it's been in the red, no. I know the sender and dash gauge aren't exactly a primary standard, but the readings are at least consistent.

I actually took a few measurements with an IR thermometer when I got back today, but didn't think to do so on the exhaust header. The outside of the upper radiator hose read right around 180f, and the rad cap was about 165f I think. Next time I'll check on the header.

I didn't fit the rad, it came with the car, which is why I know so little about it. Your comment regarding hear transfer is interesting though, and makes me wonder if it may be an issue, compounded by the sharply reduced airflow.

I think you have not just one issue.

The advice you've had regarding timing is certainly 100% correct and I would stick with that.

 

I very much distrust your alloy radiator - anyone can copy a heat exchanger but not many can calculate what you need from first principals. I've torn out loads of HE's where the end user replaced copper with SS on a like for like basis and no upsizing was done - they thought that they were going to banish pin holing (a real issue with superheated steam) and then their process fell flat on it's face - whilsy Ali isn't as bad as SS, it is still only at 50% ish of the capacity of copper.

 

What position was the dash gauge with the IT therm reading 180F? 180F is only 82C which sounds as though it should be a bit below normal - so long as the cap is holding pressure than you have getting on for 35C left without boiling. Take a look at the dash gauge next time, then measure -

 

You could also look at hoses collapsing in the cooling system - it's not unheard of. If you were brave, you could put a plain cap on the rad and fit a pressure gauge where the expansion pipe is - you can also pressurize your own system with a footpump the same way, via the expansion pipe and make sure the system is watertight.

 

In your situation I would certainly fit the tropical fan at least - it keeps mine under control in temperatures higher than yours - though of course you are facing problems of thin dry air passing through the rad.

Edited by Captain Mainwaring, 28 May 2013 - 03:32 AM.

[A-Cell]

I agree with Mainwaring about the radiator material. Copper is best for heat transfer.
From temps you took could be you have dodgy (over reading) temp indication system.
Re coolant loss, if cap is not efficient maybe coolant loss is via overflow hose.
Keep testing, you will sort it.

[sdjones121]

Ok guys, thanks a ton for all the help. I think I'll source both a new temperature sender and radiator cap just to rule them out before I go too crazy with the fan and/or radiator. When/if I reach resolution I'll report it back on this thread in the hopes it'll help someone else in a similar situation down the road.

 

Thanks again, you've been a massive help!

[Captain Mainwaring]

Nooooo...don't just randomly change out parts. You'll need to earth the sender with a temporary ground and drop it in hot water and watch the gauge. It could be going into the red at 85C, you need to find that out before swapping stuff. You could be changing the sender and it have no effect when in fact the problem is the voltage reg for the gauge or the gauge itself. 

Start off with a datum point so you know what temperature pushes the gauge into the red.

 

I'm wouldn't top up a cooling system with it running either.

It can do no harm to change the rad cap though.

 

All joking aside - brim the cooling system and then push a schrader type footpump connector on to the expansion pipe nipple and pressurize it to 1 bar or so....you'll see if the system is leaking anywhere - and before anyone says it won't work - the rad cap should have a vacuum breaker arrangement inside to allow the system to top up if fitted with an expansion tank, so you can pressurize through the rad cap.

[sdjones121]

Got a bit bored today and had noticed more gunk on top of the cores, so I decided to do another full flush. Got a bunch more stuff out of both the engine and radiator, but also took the time to get a closer look at my radiator. Turns out it's not the Mini Spares alloy rad, but is actually the crappy eBay special. Given what you've all said about alloy not cooling anywhere near as well as copper added to the fact I have about the worst radiator ever, I'm thinking that may be a large source of my problems.

 

I've also been driving a few routes repeatedly at different times and have noticed some potentially supporting behavior. Going up 1,000 more feet, during a cool evening, with an extra 140 lbs person in the car, the temp gauge didn't get near the red. Driving alone, on a level road during the heat of the day, the needle goes up super quick. Several tests have shown that elevation has little affect on running temp, but ambient temp has a massive affect. I'm wondering if that's an indication that the fan, while perhaps not ideal, is "good enough" but that the radiator itself just can't keep up when the air temp goes up to 90f.

 

I also checked a few more locations with my IR thermometer when the needle was on the edge of the red. All points on the head itself measured right around 220f/104c, same with the block. The exhaust header was around 405f/207c.

[Captain Mainwaring]

First, take the reading from an IR thermometer with a pinch of salt - treat it as a guide only. IR thermometers are fine if you realise that they are calibrated for black body radiation, in other words they will be accurate ish if sensing a matt black object only.

 

Do yourself a favour and dump that rad. I won't start a rant on chinese junk right now, but all they can do is photocopy. The fact that the tubes they use may create a greater than normal dP across the rad and thus reduce airflow wouldn't occur to them, neither would the fact that aluminium is a relatively poor conductor of heat for this type of application.

 

Ditch the thing, sell it to someone you don't like, and fit a decent copper rad. If you don't use the car heater, take the thing completely out of circuit to prevent the dead end gunging up. Give the system a real good flush and refill with good inhibitor. 

It wouldn't hurt too to fit the tropical cooling fan - but try the rad first.

[sdjones121]

The IR readings mean little to me, I think A-Cell had asked what the header measured at so I figured I'd give it a go.

 

Albuquerque actually has a pretty active British car owners club, I'm going to make contact with them and see if anyone has a radiator I can borrow to test. It's looking like that's a likely solution, but It'd be nice to see before dropping a couple hundred dollars.

 

Thanks again.

[Captain Mainwaring]

I asked to see if the header was boiling - well at least it's getting to over 100C

 

I guarantee the rad is crap - 

 

Let us know how the test goes with a copper rad

[A-Cell]

I think it's come down to 2 issues then.
The altitude running is cured by advancing the ignition. This only has a minor effect on the overheating.
The overheating is either it's not actually overheating, your temp sender and gauge is inaccurate and showing too high a reading - as Mainwaring says test it before replacing.
If it is a genuine lack of cooling then I am also with Mainwaring - Copper rads work best.
Keep buggering on....good luck, hope someone can lend you a std rad to test.