13 replies to this topic

[Matt Zane]

Good evening all,

I have finally got the car back on the road, for the first time in about thirty years. I've got a laundry list of issues to sort out including a suspected exhaust leak (the cabin stinks of exhaust) and some nasty wheel scrub at 3/4 lock, but that is not what I've come to ask about.

I've got a bit of an issue with the temperature gauge reading hot. The car seems to get up to temperature okay, but the temp gauge wanders all over the place.

Cruising around at 30 and above the gauge seems perfectly content to sit at around the middle, but dropping to a crawl or in traffic or slow speed the gauge quickly starts to rise, but will drop down again when the getting back up to road speed.

But at the end of the drive, and admittedly, it's not been farther than a few miles, the gauge rockets up when I'm putting it in the garage.

The engine has had a new water pump, hoses, thermostat and hoses. The rad was liberally flushed when I renewed the waterpump. The fan has been refitted correctly. I have also renewed the temperature sender, but the gauge is the original item.

The car does not have a heater, as I prefer the look without, and I'm not intending to daily drive it.

From the symptoms, the issue seems to point to airflow, as the temperature seems to return to normal relatively quickly when out and about, but rises when the car is stationary, but the doesn't make sense to me, as the car is a relatively stock 998, which makes me think there is an underlying issue causing the wandering temp needle.

Could this be a symptom of car having sat for such a long time? I understand that corrosion in the water jacket can cause the engine to heatsoak, but would that only present when the car isn't getting good enough airflow?

I would appreciate any direction as to what I should check first?

Thank you all in advance!

Kind regards,

Matt

[nicklouse]

Sounds totally normal to me.

 

When driving the air is pushed through the rad. When slow or stopped the fan is having to do all the work.

 

guess you have a modern car where the needle does not move unless it get out of a certain pre determined range.

[Dusky]

Regardless of what gauge you have, it shouldn’t instantly shoot up that much. How high does it get?
Then check if the system has been bled.

[Matt Zane]

Hi there!

Thanks for the responses. Yes I do have a modern car, and the only wandering temp gauge I've experienced up until this point was on an Alfa Romeo, which had a problem with eating engines. However, I am aware that temp gauges do move on classics.

I was conscious about how high the needle was reaching on the gauge, as its reaching not far off the hot end of the gauge (sorry precise degrees Celsius readings not available) which did struck me as strange.

I will take a look at bleeding the system. Would removal of the heater have an effect on the temperature too, by affectively shortening the cooling system?

Thanks,

Matt

[gazza82]

You have got the correct temp sender for the gauge? A mix will give false readings.

That Alfa: my 156 used to show the temp fairly accurately and unlike most moderns didn't just average it out an sit at a particular temp. So first thing you would watch it warm up, then suddenly drop as the thermostat started to open and dump the cold coolant in the rad into the engine, then slowly rise up again. It was also very easy to spot the time the thermostat failed and stuck open .. no sudden rush of cold coolant. I actually prefer to see the actual temp so the A-series I'm building will have a Smiths mechanical capilliary gauge.

[beardylondon]

+ for smiths capillary gauge, I was tearing my hair out with trying to find a decent sender and the old gauge on my Mk1 was also being a pain, then someone on here, I think Nick, recommended a capillary gauge and all is good, very accurate.

Edited by beardylondon, 27 January 2021 - 06:03 PM.

[Matt Zane]

Thank you to both, yeah my alfa used to do a very similar thing! Never trusted that car after the bottom end went after 300 miles of ownership.

The sender was from minispares, but I'll look into the capillary temperature gauge. I've got a handheld digital thermometer on order to check things out. I'll keep you all posted.

Cheers, Matt

[Aria Aradhea]

How's the timing of the engine? And also the carb set up?

Too retard/advance of the timing may cause heating issue. As well as the carb setup, too lean a setup can also make the car run hot.

[weef]

First off you need to determine whether the engine temperature is rising as you say or whether it is an indication problem. Once you determine where the problem lies your rectification efforts can be focused. Use an IR temp measuring or a thermal imager to scan and observe the temperature.

[Matt Zane]

Hi guys, the timing and carb were set up by an experienced mechanic a couple of weeks ago. I checked the for airlock, the coolant was a little on the low side, but nothing crazy. The car still gets between normal and hot when idling. When out on the open road it sits around normal, and climbs when I slow down or stops. I've just ordered a capillary temperature gauge. If the problem persists, I'll order a new radiator and an electric fan kit. I hope that the gauge is the issue here. I'll update further once I've fitted the new gauge.

[monkey]

If the gauge is working fine, can I ask where abouts you live? I’m far from an expert but asuming your in the UK (where it’s bloody cold at the moment) I don’t think this is normal, I struggle to get heat into mine at the moment and there’s no way she would overheat on the drive.

When you flushed the rad etc did you also flush the block? Also, do you get hot air out of the heater?

If you didn’t flush the block out then That would be my suggestion.

Hope this helps

Steve.

[roblightbody]

Is the fan on the right way round?

[Matt Zane]

Hello all,

I think I may have identified the problem this evening. I suspect I may have a dodgy thermostat. I popped to the garage after work, pulled the housing off, and removed the stat, buttoned it up, and started the car, it took ages to get to temperature, but once the needle got to N, it stayed put. I let it idle for about 10 minutes, and the needle stayed put. It's a brand new part from minispares, which I put in about 18 months ago (the car hasn't been run since i replaced it, so not wear and tear) I'll confirm this weekend when I take the car out for a spin, but I hope that is the issue. I wish I had checked that first before shelling our on a capillary temperature gauge...but it's shiny and pretty, so there is a silver lining! Lol

[beardylondon]

Pop the thermostat in some boiling water and see if it opens