'Stat testing

[Cavman]

Hi All,
I had a bout of overheating on weds on the old Cav, so parked her up and finally today set about finding what was up. to cut a long story short I reckoned the 'stat might be iffy so I whipped it out and did the old hang in a pan of water on the stove test. sure enough it started opening about 87 degrees C and was fully open by 100, the haynes manual was very pleased with this in the mean time I took the car out for a spin with no stat at all and she (unsuprisingly) wouldn't get up to temp unless sat still in traffic. so I put the stat back in and within 4-5 mins, before I'd even got off the drive, the needle was climbing fast and wasn't stopping.
So my stat isn't opening. I can also tell this because with the rad cap off theres no water movement across the top of the rad, which there is with no stat in place. this confuses my simple brain so I thought I'd put it out there for you lot to muse over!
I realise this is a bit cheeky as it's not actualy a v8 (standard 2L lump ), but it is the car that my V8 will go in when it's built!
for reference, Carb is recently tuned, timing is good, no fan belt slippage, new-ish (6000 miles or so ago) water pump, no coolant leaks, plenty of fresh oil in her (changed 3 weeks ago) and I drained, flushed and renewed all the coolant this morning before starting.

has anyone had a stat "pass" this test but still be defunct when put in an engine? any other ideas?
thanks guys!

James

[gelmonkey]

Hi James
How about trying a new stat?
Have had a similar problem in the past and a new unit fixed it.
You could also be suffering froma knackered temp sender unit as these are tempermental to say the least and can give up in a moment.
Also, do you need any bits off Malcs old Manta for spares?
He asked me to ask you as he still remembers the huge grin you had on your face after driving his car back into the Pod a few years back and would like to try and help in some small way.
Cheers
P

[Ian Anderson]

Does the Stat have a hole in it to allow bleeding before it opens?

Perhaps a couple more will allow enough to move until the stat decides to move

Or just buy a new one - not normally too pricy

Ian

[ramon alban]

has anyone had a stat "pass" this test but still be defunct when put in an engine?

Hello James, As you have discovered, thermostats love to be immersed in water to be able to open, thats why it passed the saucepan test with smimming (flying) colours, and failed the engine test miserably.

Expressed another way! You have probably been unable to expel all the air in the system and whilst the really hot bits like the exhaust valve and exhaust manifold water jackets are boiling merrily away, with zero coolant flow, the thermostat is dumb and happy trapped in an airlock and unable to open properly, if at all.

And what about the trapped air? Well it congregates in the highest part of the cooling system - just about the exact location of the thermostat. No surprise there then - so dont blame the thermostat, thats the way they like to work - immersed in water.

Mind you, there might also be other faults with your system, as yet undiagnosed.

Read all about diagnosing RV8 cooling system problems in a downloadable and print ready PDF available from here:

http://www.vintagemodelairplane.com/pag ... ing01.html



Ah, you'll say, but its not a V8? Well sucks! The general principles are the same across the board, you just have to apply them to your system.

[Cavman]

thanks for all the advice guys,
Over the last few days I have, in two stages so as to see what effects they give, firstly drilled 2 x 4.5mm hole through the 'stat and secondly made attempts to clear any air lock in the 'stat housing by parking on an uphill, then jacking up the front to add even more height, "adjusting" the rad mounting bracket up an inch or so to get the rad cap higher than the 'stat housing. then squeezing all the pipes with the rad cap off and slowly adding another pint to the system. I now get a slower warm up, as expected with the extra holes, and at anything up to 2500 revs stable-ish but mostly cooling down readings. at anything over 2500prm it slowly heats up and up. luckily my drive to work only involves ten mins on the motorway before the 50mph 'A' roads kick in and it all starts cooling down again. I'm ordering a new 'stat to see if this solves it. Can't not be able to do long journeys in it, I'll miss all the shows!

James

[ramon alban]

Hello James, Some people go to extraordinary lengths to expel air from their cooling system.



On the other hand have you tried burping it out. If not, you should be able to adapt this to your cooling arrangement.

http://www.vintagemodelairplane.com/pag ... ant01.html

The trick being to run the engine at fast idle, top up the coolant, jam on the pressure cap, wait for the glob of air to burp up, remove the cap, top up the coolant, jam on the cap, etc etc, until no more burps come out.

[unstable load]

You say in your first post you drained, flushed and replaced the coolant, but what condition is the radiator and the water pump in?

This is starting to sound like a scenario with restricted flow or cooling effect rather than a 'stat issue. It makes little sense to me that you would overheat only on the motorway with a duff stat, it has to be related to the amount of water flowing in the system and/or the cooling ability of the rad core.

If your impeller is not good then your flow will diminish regardless of revs, but an engine on a lighter load produces less heat, so cools easier. Likewise, a rad that is marginal will not cool a lot of really hot water well, but will cool less hot water better at lower power usage.

I'm probably off base here, but it's worth a stab in my opinion...

[Cavman]

thanks for the comtinued help guys, I'll be picking up the new 'stat tomorrow and I've got a new rad cap to boot to make sure I get a good seal. I figure they're only cheap things and may well help.

Ramon - love the pic! I'm going to try your tip tomorrow so I'll keep you posted

Unstable load - I was confused by the "hot on the motorway/ cool in traffic" backwards-ness, but what you say makes sense to me. The pump was new a couple of years ago but the car has covered only about 5000 miles since then, it's still shiny and new looking so I cant imagine it's that. If only I had a mini camera to view all my waterways I'd be laughing. I could scrounge a infra reed thermometer and hot-spot hunt? is there a better way to dignose blockages?

Mr Monkey - I will call you soon for a chat and say Hi to Malc for me, <--- emoticon version of said MASSIVE grin! I'd love to know what bits he has, I'm sure it's all very useful stuff

J

[ramon alban]

is there a better way to dignose blockages?

Hello James, I guess the temperature measuring process can be a bit technical, but if you review again the first link I gave you, you'll come across these two simpler possibilities.

1 (mostly on page 6, third possibility) If the radiator is badly crudded then the water temeperature at the output lower hose will be high compared to a normal situation, or expressed another way, the difference in temperature between the top and botton hose will be quite small, because the radiator it simply unable to dissipate the heat load to the air passing over the fins.

In such a case just sensing the temperatures (carefully) with ones fingers should reveal the lower hose is too hot, by comparison.

2 (mostly on page 5, headed "seriously impared coolant flow") If the water galleries in the engine are badly blocked one of the unmistakable symptoms is that the coolant temperature as seen on the cabin gauge will be unstable, varying quite a bit, depending upon driving conditions etc.

However, for both the above situations, the beauty and simplicity of flushing and reverse flushing the whole system, as two separate functions, with a garden hose to clear the crud from either or both the block and the radiator on a routine basis is so enjoyable, that its hardly worth not doing it, just for the fun of seeing all that crap come out.

It is also very cathartic, and you just know right from the get-go, its gonna solve a load of problems at virtually zero cost (specially if you saved the coolant before flushing).

[Cavman]

Ramon,

I had failed to notice the link to the entire document and had just read the web page.
less haste more speed! I'm now all over it like a rash. today will be a fun day!