NB cooling issues

[Jeo]

And putting the old cap on the new radiator seems to have fixed it! Haven't road tested it yet so no test under load, but fans are now able to control the temperature when stationary so that's definitely an improvement.

Narrator - It had not fixed it



Ohkay. ~30 minute drive each way to work yesterday. Got up to temperature then remained steady throughout the drive. But also my commute is entirely 80, 90, and 100 zones so not particularly taxing.

~20 minute drive though the city at lunchtime today, 28 abmient. Temperature was perfectly happy in the stop-and-go traffic, intersections, lights, etc. Floating between 85-95. Seemed to be the same as the efforts in the driveway at home over the weekend in that it would get hot enough to turn the fan on, drop enough to turn the fan off, then slowly creep back up again. Cycled a few times but all seemed well.

Detour via black mountain on the way home and gave it the beans. One pull to redline in first and second and we're knocking on 100. Sustained load in 2nd up the hill and it crept up to 106 before I backed out of it. Sat at the top of the hill in the shade idling and it dropped back to 90 after a few minutes. Drove normally on the way home and again it would drop a couple of degrees while idling at a set of lights, but then steadily climb while under load of driving, even when in clear air at 60kmh.

Is it new radiator time?
Short of the pump itself not flowing as it should (which I'm really not excited about) I don't know what's left that it could be. Is there any way to test the flow rate of the water pump?

[bruce]

oh joy...

[greenMachine]

I am thinking burping may be your issue. Water pump is circulating coolant, coolant is circulating therefore radiator tube seem clear and thermostat open (but is it fully open?), assume no blockage in front, within or behind radiator external fins, air in system seems the most likely cause at this point.

Nose up, get thermostat open, big funnel with a small head of coolant, occasional bursts of revs to push the coolant through, occasional squeeze of the upper hose quickly open and shut. Can take 15-20 mins, and only way you will know it is right is when you take it for a hard run and no rise in temperature.

[bruce]

I got one of those special coolant funnels. Only to realise it does not work with the custom radiator system of my car.

[Roadrunner]

I have the Lisle funnel. It wasn't cheap for a plastic funnel but worth every cent for spill free coolant filling and burping.
Jack the front of the car up high, fill till it there's excess in the funnel, run the car up to temp making sure the fluid doesn't drop below the funnel as all the bubbles come out. Once its cycled a few times let it cool down. Plug the funnel with the provided plunger and drop the contents into your overflow tank. easy as and not a drop of coolant on the ground.

Failing air bubbles in the system, it's possible your radiator is clogged internally, externally or both. If your 5 is mostly stock, the standard run of the mill alloy radiator is relatively cheap and worth doing anyway if you are unsure of the age of your current radiator.

[bootz]

FWIW I have a stock NB with the original radiator which is over 20 years old!
Because the original gauge is so useless I have an aftermarket digital one which goes by OBDII.

Some observations which I found interesting:
Original gauge does not even begin to move until approx 55 degrees
From 72 - 96 the gauge registers normal
At 96 the fan turns on and temps go down.
I have not experienced temps above 98 even when the intake temps were 65!!!
I can not therefore comment as to when the original gauge would register overheating.

Get an aftermarket gauge for peace of mind.

[Jeo]

Progress! but still doesn't seem 100%

Borrowed the funnel from greenMachine and burped the system again last night. Didn't get a lot of bubbles but did get some so taking that as at least part of a win. Car still perfectly happy idling in the driveway - would creep up to 96 at which point the fan turned on, drop back to 89 and fan turns off, repeated several times. Which again is a massive improvement from two weeks ago.

Went for a drive at lunch time today. Got up to ~85ish and held there while driving around perfectly happy. Waited until the oil temp was similar and then went for some harder pulls. Feels like an improvement as it only took a single pull to crack 100 on the coolant temp sensor the other day, whereas today took maybe 10 hard pulls from 20 - 100kmh on a reasonable incline. It was slightly cooler ambient today but only by a degree or two so I can't imagine that's the difference here. Gave it a few more pulls until I saw 105 on the coolant temp gauge, and 112 on the oil gauge, and decided to head home. 90kmh up a big hill on the way home (William Hovel for CBR locals playing at home) and even with 3.5k rpm's the coolant temperature still dropped steadily. So again, improvement from where we were before the burping exercise yesterday.

Still doesn't feel right as ignoring the new gauge and whatever number it's showing, the factory gauge never crept much above 50% before, even when on track. So getting it to 75% while admittedly beating on it but still on the street make me feel like something is still wrong.

I'm going to give it a crack at a motorkhana on Sunday and will keep a close eye on the gauges, but beyond that I think the plan will just be to drive the thing for a while and see what happens. If it copes with a regulation amount of abuse in 30 second intervals on the weekend that'll be enough for the time being. r maybe I get bored and buy a new radiator and thermostat anyway just because I've run out of other ideas. Future problem regardless.

[Jeo]

Failing air bubbles in the system, it's possible your radiator is clogged internally, externally or both. If your 5 is mostly stock, the standard run of the mill alloy radiator is relatively cheap and worth doing anyway if you are unsure of the age of your current radiator.

New (to me) radiator went in the car in November. Aftermarket unit to factory specs, apparently was used only for a few months before upgrading and was then given to me from a club member. He still even had the box it came in and had kept it as a spare after upgrading, but saw my plight of an off track excursion the day before another event and offered to help.

[Roadrunner]

Thats good. So not likely radiator related.
Keep a very good eye on the temp gauge at the motorkhana, it's a lot of engine load while bouncing off the redlline without much forward movement for airflow. It'll push the limits of most cooling systems.

[Jeo]

Post stolen from main garage thread. Wrote it there first but then realised I should probably include it here for future sake as well.

And motorkhana yesterday. The setup the MG club runs is six tests over the course of the day, two setup at once which you run back-to-back, with two attempts at each course. So overall it runs like 30~60 second course, ~60 second break, 30~60 second course. Repeat 6 times over several hours.

First run was fine cooling wise. Test 1 and 2 with no dramas, factory gauge showed normal and I don't remember what the aftermarket gauge said but it wasn't excessive. And then I got greedy... The line for my second go at test 1 was empty so I pulled straight back around and ran it again. Turns out three tests with only a minute or so break in between each run was too much. Didn't boil but the aftermarket gauge was showing coolant at ~108 and factory gauge well into the red. I pulled out of line and let it idle for a few minutes and the temperature quickly fell. Had another run and climbed back up to the low 100's again. Drove back up to the pits and again let it idle for a few minutes.

Rest of the day was uneventful temperature wise but I'm putting that down to good management, rather than anything having magically fixed itself. Tried to space out my runs for the rest of the day so that I had at least 30 minutes between passes, and that worked fine. Aftermarket gauge was always showing low 100's after the 2nd run, but would quickly drop after a little idling in the pits.

Still not sure what the problem is but instead got frustrated and took the "well nuts to this option". Even though I'm relatively confident both are fine, I bit the bullet last and ordered a new high flow thermostat and ebay special alloy radiator. So here's to that solving it?