Needle says i'm overheating - could it lie?

[tamper]

Since getting my engine replaced, I've had some (probably unrelated) overheating problems. Whereas previously the gauge would go from cold to dead centre (and stay there), now once warmed up it starts to swing back and forth from center to overheat as I drive.

My expansion bottle looks normal, but the radiator was low on coolant. I topped it up, and things were fine for a few days. Now it's swinging again. My first thought is a radiator leak, which it still could be, but there's no tell-tale pool of coolant on the ground when parked. I do notice a lot of bubbling at the expansion bottle after stopping, but maybe this is normal?

Strangely (or possibly not?) when the needle indicates overheat, I turn the fan on full to dissipate into the cab, yet the air coming out isn't especially warm.

Is there anything other than a radiator leak I should look for? If it is a leak, should I try pouring in that gumming-up formula stuff?

Thanks guys,
tamper

[BUSHWHACKER]

Sounds like you've got an air-lock in the cooling system.

[tamper]

Sounds like you've got an air-lock in the cooling system.

I thought that too, and tried 'burping' the radiator, but to no real effect. If that's what it is, is there another way of clearing an air lock?

[BUSHWHACKER]

Remove rad cap, set heaters to hot, including rear heater if you have one, run engine up to temp. (until thermostat opens) while topping up coolant.
When you can pour no more in, replace rad cap and shut off engine.

[tamper]

Remove rad cap, set heaters to hot, including rear heater if you have one, run engine up to temp. (until thermostat opens) while topping up coolant.
When you can pour no more in, replace rad cap and shut off engine.

Thanks mate - just so I'm clear, I'm supposed to be running up to temp WHILE topping up coolant (so from cold)? Or run up to temp and top up coolant after that?

t

[BUSHWHACKER]

Top up with a stone cold engine. Also the expansion bottle should only be about a third full when cold, basically just enough coolant to cover the end of the tube, (plus an inch) that goes inside.

[TonyN]

A small leak, especially on the rad may go unnoticed as the water coming out get evaporated from the hot rad, instead of dripping down.

If the heater is blowing cold and temp is hot is a sure sign your low on coolant, (as long as the heater worked before, and isn't blocked) You need to find where is leaking from.

Don't let is overheat to often, even the better designed heads, like any other car, will only take so much heat before you crack them.

There was no hint of problems when you had it up here for the oil change a couple of weeks ago.

[tamper]

There was no hint of problems when you had it up here for the oil change a couple of weeks ago.

Cheers Tony,

Yeah it was fine after coming to see you - just started about a week later. I'm just unlucky I guess, or else the Surf's 14 year vintage is starting to show!

Incidentally, the oil pressure gauge has lately starting swinging into the lower quadrant too (then back to normal), yet the dipstick shows normal oil level. I don't know if this could be in any way related to the radiator problem - it's just that both things started around the same time.

Do you perchance do rad repairs?

[TonyN]

Cheers Tony,

Yeah it was fine after coming to see you - just started about a week later. I'm just unlucky I guess, or else the Surf's 14 year vintage is starting to show!

Incidentally, the oil pressure gauge has lately starting swinging into the lower quadrant too (then back to normal), yet the dipstick shows normal oil level. I don't know if this could be in any way related to the radiator problem - it's just that both things started around the same time.

Do you perchance do rad repairs?

Sounds like your guages are going nuts!! You could have a wiring problem on the motor earth leads, this might affect how the senders read.

When you say the oil pressure is moving, is this when at a constant speed, as the guage will be different at idle than at 3000rpm.

Can't easily see how you'd get a verying oil pressure without something very odd going on.

I can get recon-ed rads and fit then, or minor holes I can solder up.

[tamper]

Sounds like your guages are going nuts!! You could have a wiring problem on the motor earth leads, this might affect how the senders read.

When you say the oil pressure is moving, is this when at a constant speed, as the guage will be different at idle than at 3000rpm.

Can't easily see how you'd get a verying oil pressure without something very odd going on.

I can get recon-ed rads and fit then, or minor holes I can solder up.

Tell me about it! Oil pressure gauge does go down when idling, but I expected that. It's more that it can then stay at 1/4 (rather than 1/2) for a while at 3000rpm+. As I say, the actual level seems okay so maybe I'm worrying too much - but after last time, I'm paranoid!

I think the rad is definitely a leak - just had to top up 3 litres of coolant since last weekend. I think it's time I paid you another visit!