Temp gauge moving up and down

Temp gauge moving up and down

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Discussion

tbernd

Original Poster:

91 posts

134 months

Wednesday 17th September 2014
quotequote all
Hi mates,

i've got the problem that the temp gauge is moving up to 110° and after some seconds it moves to 85°. Sometimes it stays a bit longer but it's moving around without any visible reason. The cooling system is, as the whole engine new and seems to work good. The fan never starts when the gauge shows 110°. The sender is at 46 ohm when the fan comes.Maybe there is a ground problem? Where is the ground for the instruments ? Perhaps any ideas?
Thanks.


Cheers

Bernd

honestjohntoo

576 posts

215 months

Wednesday 17th September 2014
quotequote all
tbernd said:
The fan never starts when the gauge shows 110°.
That is because the temp sensor is measuring temperature inside the inlet manifold and the fan sensor is elsewhere, probably in the radiator or cowl near the top hose.

tbernd said:
the temp gauge is moving up to 110° and after some seconds it moves to 85°. Sometimes it stays a bit longer but it's moving around without any visible reason.
You probably have trapped air in the cooling system that allows the extremely hot parts of the engine near the exhaust manifold to boil the fluid and generate super-heated steam. That steam navigates its way to the inlet manifold, cooling as it goes, where the temp sensor resides.

Even so, the gauge reads very hot, before the system flushes cool fluid around to immediately show the lower temperature.

And so it goes on, without any reason to stop this absurd cycling.

To fix the problem you have to burp the trapped air from the system.

TVR's probably have a special method for this that I don't know about - but someone will.

Another possibility is your pressure cap has failed allowing the engine to boil at approx 100 deg C.

Here is some special reading material, although written for an SD1, it approaches the issue from the point of view of achieving a stable engine temperature. However, much of it may apply to TVR.

http://www.vintagemodelairplane.com/pages/Snippets...

http://www.vintagemodelairplane.com/pages/Rover_Te...

The Hatter

988 posts

169 months

Wednesday 17th September 2014
quotequote all
Does this happen only when the engine's warming up or all the time?

Both my Wedges do this as they warm up with an 88 Deg 'stat fitted; it's worrying so I run 82 Deg stats. I'm pretty certain I don't have any air locks and the head gaskets are OK. I spent ages trying to sort out the 'problem' but now I'm satisfied that it's a TVR 'characteristic'. I know that TVR used a different/larger thermostat so they clearly had issues, plus they tried several coolant pipe configurations over the years so I suspect they never got the cooling system to work properly.

The SD1 had an engine driven cooling fan in a steel body, TVR had an electric fan in a fibreglass body... I think that's the 'problem'. If someone can correct me I'd be very happy; I'd love my tempgauge to hover around the middle all the time!

ElvisWedgely

2,714 posts

164 months

Wednesday 17th September 2014
quotequote all
I've owned five different Wedges but never had that problem with any of them. They do tend to run hot and hover around the red mark when the fan kicks in. Guage moving up and down eretically doesn't sound right. Possible air lock or pressure problems but doesn't sound like a serious problem as the car is not overheating.

Tony. TCB.

adam quantrill

11,535 posts

241 months

Wednesday 17th September 2014
quotequote all
It could be because of a very small leak, get it up to temp and then some, then kill the engine and listen for any hissing.

The wedge system cam lead to more trapped air than the SDi so it's more prone to air - and steam - accumulating near the thermostats.

tbernd

Original Poster:

91 posts

134 months

Wednesday 17th September 2014
quotequote all
Hi,

it happens all the time. You're cruising around and suddenly the gauge rises. After a short time it goes down . Sometimes it' even stable.Maybe there's some air in the system.


Cheers
Bernd

honestjohntoo

576 posts

215 months

Thursday 18th September 2014
quotequote all
tbernd said:
Maybe there's some air in the system.
I'd bet there is.

How to burp the RV8 (I am familiar with)

  • Easily cured problems are ageing hoses/components, crud in the system and blocked water galleries but tiresome airlocks are a common cause of unstable temperature and low efficiency. Eliminating them is a mystery verging on black art and this is my solution to that problem.
  • Faulty components such as thermostat, pressure cap, leaking hoses/joints, etc, can be readily tested and replaced. Fitting a thermostat with a jiggle pin makes for easier filling when the time comes. Radiator can be re-cored and engine block, heater matrix and radiator can be easily back-flushed using a domestic hose. Caustic soda solution can be left in a matrix for a few hours to loosen lime-scale deposits before flushing again. Loads of crud can be purged from a neglected system in a short time. Refill the system with plain water and bring the engine up to temperature with a short run to further loosen stubborn residues then check for obvious leaks before emptying.
  • With heater controls set to "hot", the radiator filler plug and pressure cap removed, refill with appropriate coolant via the radiator filler hole using a funnel until the system is full. Rock the car a little to encourage coolant to flow through the system and when the radiator stays full, replace the filler plug finger tight ensuring it has a good seal. Fill the expansion tank and with the pressure cap off, run the engine until hot and watch fluid rise and fall in the tank as bubbles escape with an occasional burp purging air from the system. When the engine is hot and bubbles/ burping slow down, stop the engine, remove radiator plug and top up the radiator again.
  • Raise the idle speed to 2000 rpm and watch the level in the expansion tank rise and fall as burps come and go. Keep the idle speed raised, fill the expansion tank and screw on the cap. Lower the idle speed for a minute as the system sucks in fluid to replace the burps. Remove the pressure cap and raise the idle speed again. It's normal for the level to go down and stay down. Repeat the above few steps a couple of times, including topping up the radiator until eventually no burps and very little level change occurs as the idle speed is varied. Close the system and take the car for a run to check the temperature remains stable under all road conditions. If it does not stabilise, carefully release the pressure and repeat the topping up process as described.
  • If a very small head gasket leak over-pressurises the system forcing fluid from the overflow there is a way to cheat the problem. Route the overflow pipe into a flat plastic bottle (0.5 - 1.0 litre) secured on the chassis rail below the tank to catch expelled fluid. As the engine cools, the resultant vacuum sucks fluid back into the system preventing continual topping up. It doesn't work for larger head gasket leaks. Amazingly, filling the bottle automatically tops up the system as the engine cools and is completely safe as the cap need not be removed.
.
Hope this helps?
.
Somebody may have a definitive process for your TVR.

Ian350

316 posts

177 months

Thursday 18th September 2014
quotequote all
I seem to remember that on mine there was no radiator filler stopper that I could get to but there were two pressure caps, one on top of the expansion tank and one on the steel pipe towards the front of the engine (is this the swan neck pipe?). To expel the air I ran the engine with both pressure caps removed and topped up through the aperture on the pipe. It was extremely simple and worked a treat,

erik350i

35 posts

257 months

Thursday 18th September 2014
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I've had the same problem. Tightening all the hose clips solved it for me.

adam quantrill

11,535 posts

241 months

Thursday 18th September 2014
quotequote all
Exactly:

adam quantrill said:
It could be because of a very small leak, get it up to temp and then some, then kill the engine and listen for any hissing.
The hissing is the loose clip (or a split hose).

tbernd

Original Poster:

91 posts

134 months

Thursday 18th September 2014
quotequote all
Hi mates,

I think Ramon gave the right hint. Today I tried to get some air out of the system. And a big bubble came out and the system worked a lot better. I think it's so difficult because the engine was empty after the rebuild. When I worked only on the water pump and I refilled the system it was no problem.
Thank you all for your advice especially to Ramon.

Cheers

Bernd

adam quantrill

11,535 posts

241 months

Thursday 18th September 2014
quotequote all
Good news - I have my own method for refilling which is to leave the swan neck cap on and undo the thin pipe that runs to this - but at the expansion tank end.

Then attach a funnel to the thin pipe, raise it as high as possible and pour in coolant.

The expansion tank will burp air and then eventually the level will rise. Also try squeezing the bottom rad hose to promote more burping.

This way I never disturb the swan neck cap and it lasts forever.

tbernd

Original Poster:

91 posts

134 months

Tuesday 28th October 2014
quotequote all
Hi mates,

unfortunately my problem is not solved.
Evertime I think the air is out of the system and I drive a bit the problem with he rising gauge is there again. When I let off the throttle bublles occur in the expansion tank. Maybe it´s the head gasket but compression is good, every cylinder 170 psi.The engine was out last winter and I (the engine builder)changed from the thin gaskets to the composite ones.
Any idea??

Cheers
Bernd

mrzigazaga

18,534 posts

164 months

Tuesday 28th October 2014
quotequote all
Hi Bernd...Is the car actually getting that hot?...Have you checked the temperature with a laser pointer thermometer on the rad and associated pipework?..
If you have a temperature control switch for the fan what is it set to?..You need to make sure the thermostat is able to open fully...

Ideally you want the car on level ground, The swan neck is meant to be filled before the expansion tank..The cooling system does leave a lot to be desired so sometimes the system takes a while to bleed..You don't need to fill the expansion tank up too much..You only need around a third to half as its a closed loop system which means the water will expand in the expansion tank and be drawn back in to the system as its allowed to cool.

Ideally a fan should be kicked on a few degrees after the thermostat has opened..I think Normal operating temp for the V8 is 88-90 degrees?

I think first see if it is getting that hot or if its an electrical problem with the gauge.

Cheers...Ziga

tbernd

Original Poster:

91 posts

134 months

Tuesday 28th October 2014
quotequote all
Hi Zig,

Thermosthat is 82°, Fan-switch ist 92-87° both new and good quality. If the car moves the fan sometimes works sometimes not when the Temperatur rises, if the car stands in the garage the fan works erverytime.Everything else on the cooling system is new or reconditioned. I´ve tried the Laser thermometer. The Temperatures at the temp-sensor are the same as on the instrument.
Before the engine rebuild bleeding the system was no problem.
I´m really puzzled.
Cheers
Bernd

wooly350i

2,248 posts

207 months

Tuesday 28th October 2014
quotequote all
I seem to remember this going on with my previous engine, don't forget the swan neck always empties of water when its cooled down so is full of air and will start filling again on warm up so the air that's collected in it is pushed up that little pipe to the expansion tank or most of it should anyway. I think this is where the design is a little floored because we then have water trying to overcome air at a high point which in plumbing terms ain't ideal.scratchchin
If there are any tiny leaks it could suck air into the system when cooling as the water contracts and will collect at its highest point being the swan neck. We can always bolt a 40 gallon water tank to the boot lid and pipe it through to the engineidea

adam quantrill

11,535 posts

241 months

Wednesday 29th October 2014
quotequote all
what doesn't help here is if the air bubble in the swan neck backs up to the thermostat and then it doesn't open for a while because it's surrounded by air.

One thing to check is that the thermostat element was installed with the "jiggle pin" at the top (please correct me if I'm wrong but I think that's the correct way) so it allows air to bleed.

Do you get bubbling from the overflow pipe when the engine is running and hot? If so it might have acquired a small cylinder head leak. I diagnosed this on mine by:

a) running the bubbles through a lime solution - it will go cloudy if there is CO2 present
b) disconnect the injector electric connectors one at a time - when you get to the culprit, the bubbling will stop fairly shortly. You only need to check the end cylinders on each bank for this as they are next to the water jackets - 1 2 7 and 8. YOu can take it for a short run like this to confirm - it drives a bit lumpy but does no harm.

The Hatter

988 posts

169 months

Thursday 30th October 2014
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Bernd, Do you know what make of head gasket was fitted to your engine? I also have had this problem; I have changed my head gaskets to composites from Rimmers but I'm not convinced of their quality. I'm doing a load of work on the car at the moment (Megasquirting...) and I've almost convinced myself to pull the heads off and put Felpro gaskets on it. It's nearly wintertime after all and what else is there to do??!!

MrPicky

1,233 posts

266 months

Friday 31st October 2014
quotequote all
I have also added some bits to the compression test thread about the cooling system.

tbernd

Original Poster:

91 posts

134 months

Friday 31st October 2014
quotequote all
Hi Martin,

don´t know the exact make but I bought them from v8engines. They were mounted by an engine builder and he didn´t complain about. But it looks as if i´ve solved the problem. Last winter I dismantled the heater box and changed the original rad inside to a one from a Fiesta. I changed the routing of the hoses and there seems to be a leak where air is sucked in. Two days ago I disconected the heater and tried the car on my way to work (Berlin city traffic) and everything worked fine. The needle of he temp gauge is nearly glued to 90° and the fan works as he should. I bleeded the sysem over the small hose of the swan neck. Car was jacked up and a longer hose attached. Today I´m going to work with the car and I hope it works again then she´s layded up for winter. Time for fixing the other issues.

Thank you all.

Cheers

Bernd