| Author | Message | ||
     Mark Anson Prolific User Username: bentleybloke Post Number: 67 Registered: 11-2004 |
Thank you all for your advice on the replacement of my temperature gauge. I am going to buy an aftermarket gauge with a capillary tube as these seem more accurate, also the sensor will fit inside a radiator top hose to save me finding a perfect thread fit for the original sensor hole. My problem is there are so many types of gauge starting and ending at different readings. What should the temperature (in F) be at normal so I can buy one that covers all probabilities? Please remember I am in the UK and don't have the same hot weather as OZ etc. Many thanks Mark | ||
| Robert Wort Grand Master Username: robert_wort Post Number: 221 Registered: 12-2004 |
You cooling system is atmospheric and not pressurised, so the boiling point will be 212 degrees Fahrenheit. If you get a guage in Celsius, the boiling point will be 100 degrees.Oops! Almost forgot. Assuming that you are using coolant (I hope so), instead of just plain water (a definite no no), your boiling point will be raised to approximately 220 degrees Fahrenheit or 105 degrees Celcius. | ||
| Bill Coburn Grand Master Username: bill_coburn Post Number: 463 Registered: 4-2003 |
Sorry Robert, the cooling system may be atmospheric but more likely presurised through the steam valve as it was quaintly called. That's the thing with the screwed in plug on the top of the header tank. For a while they deleted this until owners objected to the car micturating at the traffic lights so they went back to pressurising it. The original figure was about 4 psi! | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 841 Registered: 4-2003 |
Actually, Bill, the final system is at atmospheric pressure. True, the steam valve plunger was reintroduced, with a new soft spring. The final steam valve plunger is, however, drilled hollow so that the system is normally at atmospheric pressure. The drilling reduces splash overflow on hard braking. The systems went to atmospheric pressure early in MkVI production due to chronic coolant leakage into the engine oil.... RT. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 843 Registered: 4-2003 |
 | ||
| Mark Anson Prolific User Username: bentleybloke Post Number: 68 Registered: 11-2004 |
WOW as usual the replies are outstanding...drawings too! Thank you for that. Excuse me for sounding a bit thick, but what should the running temperature be? I am presuming boiling is not the ideal temp to be running your car all day. I also made a mistake in my question. The gauges are in Celsius not Fahrenheit. On my modern day car the gauge just says cold, normal and hot, I think the Mk VI says something similar (can't remember what the gauge looks like as it has never worked). Does anybody have a stand alone gauge and can tell me what there temperature readings are under normal driving conditions? Also what difference does running the car at atmospheric pressure make? Many thanks Mark | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 844 Registered: 4-2003 |
72-76C | ||
| Ashley James New User Username: ashley_james Post Number: 7 Registered: 2-2005 |
Please have a look at Norman Geeson's Cylinder Blocks and a few deviations in the technical section of www.kda132.com for full picture. Most thermostats are 78 degrees and the gauge may reach nearly ninety on hills, in traffic jams and very hot weather. Early cars have more problems because of the angle of the radiator slats. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 852 Registered: 4-2003 |
Correct on 78 degrees or so: that is the nominal thermostat opening temperature. On calibrated running temperature, under any condition (and B174UM has seen them all), I have known that there is a problem in my car if it reaches 80 degrees C. That only ever happened with a cracked head, and once with a partially blocked core. Over its entire life, the behaviour has never changed without a problem existing somewhere. I have a few bellows thermostats, and they start to open a little below 78C: by 72C they are just starting to open partly. Above 80C it is a case of dimishing returns as the flow does not increase much above that point. My experiences are that, once the system is effectively fully loaded, it's a slippery pole towards boiling. Of course, it has the MkVII radiator which may be more effective. | ||
| Bill Coburn Grand Master Username: bill_coburn Post Number: 466 Registered: 4-2003 |
Thank you Richard I stand corrected. | ||
| Mark Anson Prolific User Username: bentleybloke Post Number: 72 Registered: 11-2004 |
Thank you for your advice. I purchased the modern gauge and I have fitted it in the car. My only problem is were the sensor is to go. The original thread is the wrong way around on the plug that sits in the block. I have removed this now and cut the male thread off. Included with the gauge was a brass adapter. I am looking for an engineering shop now to drill the original plug out and tap a thread for the new brass adapter. I will let you know how I get on. Cheers Mark | ||
| Bill Vatter Frequent User Username: bill_vatter Post Number: 12 Registered: 9-2004 |
Comment concerning water vs coolant: Both straight water and coolant (50-50 mix of ethylene glycol and water) have advantages and disadvantages. The big plus for straight water is that it cools better than glycol. This is because the thermal conductivity of water is higher than that of ethylene glycol. Glycol-based coolant will boil at a higher temperature than water, which is good because the engine will run hotter with glycol than with straight water. An overheated engine might not boil with glycol-based coolant; however, if you have straight water, it might not overheat. Straight water needs corrosion inhibitors to prevent corrosion. These are principally an oxygen scavenger, and a pH buffer. These are present in glycol-based coolants but don't last forever. That's why you need to change coolant every couple of years. In my opinion, you can do very well with plain water (corrosion inhibitors added of course) unless your car is subjected to below freezing temperatures. If there is any possibility of freezing, you need to have the appropriate amount of glycol or freezing water will break the block. The water jacket outside wall on the right side of the block is very thin, has no contour for strength, and cannot abide any freezing. Block cracks that Norman referrs to in his treatese "Cylinder Blocks and a Few Deviations" are caused by overheating in the area around the exhaust valves and in the deck bridge between the exhaust valve and cylinder. For good health in these areas, you want a high thermal conductivity coolant (water is the best) and high velocity coolant (high-speed water pump) to make sure steam pockets don't form. A water distribution gallery with optimally-placed water jet holes also helps, as Norman's article addresses in depth. |
