12 replies to this topic

[mbolt998]

My cylinder head, around near where the sender unit for the gauge is, is measuring about 107 degrees C or so, and the gauge is saying close to H. I then left it idling for a good 10 to 15 min, and it was still at around 107, maybe dropped to 105, and the gauge went down a tiny bit.

 

My question is, what should the temperature be at the head with the laser IR? I'm trying to understand whether I have a real overheating problem.

 

I've only recently started driving the car again after 25y off the road and can't remember what the gauge used to do although I don't think it said it was that hot. It's got a recent new rad, hoses and thermostat, and the heater blows nice and hot. Water level is good after you let it cool down and take the cap off.

 

It's the Smith's style gauge (triple instrument facia, 1979 "Deluxe" car, 998cc)

[mad4classics]

Pretty sure last time I checked I got within a degree or so of the thermostat rating pointing around the water elbow.
Will have a check when I'm next out.

[JonnyAlpha]

How bizzare, I have just this week started my newly rebuilt engine, trying to run the CAM in. I think I am having cooling problems as the gauge is reading hot after about 2 minutes of running.

 

The Instrument Cluster is the original 1982 HLE 1000, but the temp sender is a new one from MiniMine, I think its a GTR101. 

 

I have an IR gun, but don't know how accurate it is. After it got up to about 3/4 on the gauge tonight I turned it off and its showed about 80 at No4, but showed 40 off of the Radiator. Iv'e since been told that the IR guns don't like shiny surfaces.

[mbolt998]

Pretty sure last time I checked I got within a degree or so of the thermostat rating pointing around the water elbow.
Will have a check when I'm next out.

Thanks, I'll check there too. By the "water elbow" do you mean that aluminium thing that actually has the thermostat inside it?

[mad4classics]

Pretty sure last time I checked I got within a degree or so of the thermostat rating pointing around the water elbow.
Will have a check when I'm next out.

Thanks, I'll check there too. By the "water elbow" do you mean that aluminium thing that actually has the thermostat inside it?

Yes sorry thermostat housing, unless you've polished or painted yours will be quite dull.

[mbolt998]

 

 

Pretty sure last time I checked I got within a degree or so of the thermostat rating pointing around the water elbow.
Will have a check when I'm next out.

Thanks, I'll check there too. By the "water elbow" do you mean that aluminium thing that actually has the thermostat inside it?

Yes sorry thermostat housing, unless you've polished or painted yours will be quite dull.

 

What confuses me is that you'd think the temp the thermostat opens is the temp it's all supposed to be-- that way if for whatever reason the cooling system was cooling too much, the stat could close and keep it all just right. But it's surely supposed to run at more than 88C or so (what the stats are rated at) or it wouldn't be pressurized. In any car if you just crack open the cap on a hot engine it's going to boil, implying the temp when running normally is supposed to be a bit over 100.

[sonscar]

The hot water expands so building up pressure.In localised spots the water could be considerably hotter than the thermostat.Maybe,possibly,Steve..

[mad4classics]

As SONSCAR said you don't want localised boil points particularly round exhaust valves etc. Straight water gives 0 to 100 Deg but is pressurised (+1 degree for every 0.6lb in² increase ???) to extend the high end and added antifreeze to lower the bottom end.

A quick measure with IR Thermometer gives 86.5, 86.5, 86.4, 89.4, 87.4 at the five front stud locations (88 stat). IR gun gives an indication of things but yes shinny surfaces give strange results because it's set for a nominal emmisivity. Tried it on saucepan full of boiling water and gives 65 on the stainless pan exterior and 97 on the bubbling water surface.

The temp gauge also is just an indication to give you a nice warm feeling things are ok.

Edited by mad4classics, 29 May 2023 - 05:32 PM.

[mbolt998]

As SONSCAR said you don't want localised boil points particularly round exhaust valves etc. Straight water gives 0 to 100 Deg but is pressurised (+1 degree for every 0.6lb in² increase ???) to extend the high end and added antifreeze to lower the bottom end.

A quick measure with IR Thermometer gives 86.5, 86.5, 86.4, 89.4, 87.4 at the five front stud locations (88 stat). IR gun gives an indication of things but yes shinny surfaces give strange results because it's set for a nominal emmisivity. Tried it on saucepan full of boiling water and gives 65 on the stainless pan exterior and 97 on the bubbling water surface.

The temp gauge also is just an indication to give you a nice warm feeling things are ok.

Thanks for this, very helpful. My cylinder head is not shiny, but dark green and oily. I tried warming it up from cold. When the gauge reaches N the temp is 98 at the head and about 76 on the thermostat housing (which is a bit shiny-- shiny things look colder than they are with IR thermometers).

 

Leaving it just idling for another 25m or so and it crept up to 101 at the head and around 80 on the stat housing, with the gauge going just above normal.

 

If I go for a drive then after a few miles it typically gets hotter than that (about 106 at the head) and then seems to stay there even after idling for at least 10m, with the gauge quite near H.

 

All of this makes me suspect the thermostat. I might try just taking it out and going for a drive and see what happens. My theory is the engine is slowly accumulating heat (much faster if you drive than if you just idle, but it still only happens after a few miles). But the stat housing staying at around 80 when the engine is 106 makes me think the stat is keeping hot water in there a little too much. But hard to say especially as it's a different colour. Maybe I'll paint it black. I have some black high temperature paint.

[Steam]

Not a good idea to run without a thermostat, even for testing you will not get an even result. At the very least use a stat with the guts removed but a cooler stat would give the most useful info.

[mad4classics]

Thanks for this, very helpful. My cylinder head is not shiny, but dark green and oily. I tried warming it up from cold. When the gauge reaches N the temp is 98 at the head and about 76 on the thermostat housing (which is a bit shiny-- shiny things look colder than they are with IR thermometers).

 

Leaving it just idling for another 25m or so and it crept up to 101 at the head and around 80 on the stat housing, with the gauge going just above normal.

 

If I go for a drive then after a few miles it typically gets hotter than that (about 106 at the head) and then seems to stay there even after idling for at least 10m, with the gauge quite near H.

 

All of this makes me suspect the thermostat. I might try just taking it out and going for a drive and see what happens. My theory is the engine is slowly accumulating heat (much faster if you drive than if you just idle, but it still only happens after a few miles). But the stat housing staying at around 80 when the engine is 106 makes me think the stat is keeping hot water in there a little too much. But hard to say especially as it's a different colour. Maybe I'll paint it black. I have some black high temperature paint.

 

 

If you think the temperature is climbing another thing to check is that the radiator is dumping heat ok; I get 88.4 on the top header and 57.5 on the bottom if I measure quick enough - bottom starts to climb a little if I leave it idling.
 

[mbolt998]

Well update to this: I tried dunking my new GTR101 (and the old sender unit, which has the same resistance, and both of them are basically fine I think) in some hot water with the ignition on, a wire to earth, and the usual wire into the back. The gauge reads N at only around 70°, or even less, with 88°C (where normal should be for my car, a 1979 Mk IV) about halfway between N and H.

 

So I put the 88°C thermostat back in, which is the correct one, and drove about 30 miles. Temp stayed around that point midway between N and H with some variation. Conclusion: that is the "new normal" for my car. It's fine. Quite possibly I need to look at the voltage regulator as others have mentioned. But she's not really running hot.

[mbolt998]

Another update for anyone still interested in this :) My gauge calibration was off. The surface of the water was 70°C with the IR gun but I measured again with a proper alcohol bulb thermometer and it was more like 90°C in the interior where the sender was.

 

So my sender and gauge was OK: 90°C for N. I then tested boiling water and found that 100°C was about halfway between N and H. That would put H at about 110°C. These seem to correspond fairly well with IR temps on the head.

 

I got a new solid-state VRU anyway, which I measured to be 9.97V. The sender and gauge gave similar results, so I think the old VRU was probably OK.

 

Then I thought it was still running a bit hot. I changed the water pump (old one looked fine) and the bottom hose (it looked a bit kinked so I got one with a better bend in it). No effect. Running out of ideas I upgraded the rad to the Moss "performance 3 core" (GRD4442TDF). I had been running the "standard" GRD210.

 

Curiously the "standard" GRD210 looks like it's 3 core as well. The cores look very similar. The "performance" one may have bigger tanks though. But some of the tubes in the "old" one (it had only been on there for 100 miles or so) looked a bit blocked. It took a while to boil all the rust flakes out of the engine from sitting for 25y maybe. The coolant looks much cleaner now so fingers crossed.

 

I'm now now getting fairly nice normal temps on the gauge-- usually a bit above N though. However the weather has also cooled down a little bit. Searching around it seems that the cooling power of a radiator is proportional to the temperature difference between the hot water and the outside air. This means that if the weather is 10°C warmer then under the same conditions your coolant will be 10°C hotter (assuming it's all limited by the cooling system, and not the thermostat, which in summer in a Mini it probably is).

 

10°C on my gauge is about 1/4 of the scale. So quite a big change, and we did have temps of nearly 30°C when I was first messing around with all this.