Overheating Roadster

[stevejgreen]

Re: Overheating Roadster

It should be easy, but it isn’t, that’s why the same conversation has been had many times since the first 1800 roadsters were built.

[boustrophedon]

Re: Overheating Roadster

You guys are missing the issue

The way to understand what is happening is simple - two temperatures - in and out of the radiator

That will immediately tell you where the problem is

Then you can work on radiator and air flow - or water flow and water pump and thermostat

Without doing that simple measure its all guesswork

I agree, this should be easy to arrange. There is absolutely no need to over complicate the discussion.

[stevejgreen]

Re: Overheating Roadster

You guys are missing the issue

The way to understand what is happening is simple - two temperatures - in and out of the radiator

That will immediately tell you where the problem is

Then you can work on radiator and air flow - or water flow and water pump and thermostat

Without doing that simple measure its all guesswork

If only the real world was that simple.

Assuming that you can get calibrated thermometers/thermocouples actually in the water flow, what temperatures should we be looking for at the top and bottom hoses, and what temperature difference should be found, and at what point are these measurements of significance, presumably only when the vehicle is overheating, not from a cold start.

Of course atmospheric air temperatures will have to be considered in any calculation as it has a considerable impact, along with the airflow rate through the radiator depepending on the speed of the vehicle and assuming free flow of air and no turbulence from any leading vehicles. You would also have to consider the cooling system water pressure as that has a direct impact on temperatures.

Valid measurements can only be taken whilst the car is in motion i.e. with the engine under load, bonnet closed etc. The second you stop the engine, airflow and water flow cease, and heat soak becomes an issue.

Ultimately a ducted fan in front of the radiator, forcing air through, is a solution for a roadster, but that will simply mask any latent problems like poor ignition timing / mixture and the use of ethanol fuels etc.

If only it were that simple, overheating would not be a perennial (hot summer) issue, there are just too many variables in real life.

[duncan]

Re: Overheating Roadster

You guys are missing the issue

The way to understand what is happening is simple - two temperatures - in and out of the radiator

That will immediately tell you where the problem is

Then you can work on radiator and air flow - or water flow and water pump and thermostat

Without doing that simple measure its all guesswork

[stevejgreen]

Re: Overheating Roadster

Hmmmm my experience with water pumps feeding high pressure steam boilers says otherwise.

Unless you are a professor in fluid dynamics which I am not, I would not jump to conclusions.

In an overheating automobile engine, you are not dealing with water alone But a mix of water and antifreeze, it should be under pressure, until the radiator cap or hoses blow, but the pressure is not the same through the whole system. There are areas of lower and higher pressure either side of the water pump, these can be the source of cavitation as the fluid flashes off to steam on a very small scale, there are plenty of YouTube videos describing the phenomena on large and small scales.

The vast majority of discussion points being raised here are addressed in my document that attempted to draw together all the various MOC sources of information into one place, many of them from the first days of the MOC and Pitstop.

If I have specific errors in that document I will happily correct them. It’s been downloaded almost 1500 times, with no specific adverse comments yet.

[boustrophedon]

Re: Overheating Roadster

I agree that speeding up the water pump shouldn’t cause extra stresses on it but wouldn’t that speed up the water flow through the radiator and therefore not cooling it enough before it enters the engine again.
Cheers, Martin.

No. The rate of heat transfer is zero at zero circulation. At a very slow speed it's a little better and as the water speed increases the heat transfer increases asymptotically to a maximum, it doesn't go up then down again with increasing flow.

[martinclan56]

Re: Overheating Roadster

I have been watching this thread with interest as I have just bought a roadster, with a B series engine, for restoration. I'd like to make a couple of remarks.
1. Even the newest B series engine is pretty old now and no doubt the waterways will be full of cr4p not helping the situation. Unless of course the engine has been properly rebuilt and had a good chemical clean. Hot tank I think they used to call it.
2. When fitted in the MGB did not the B series engine have an oil cooler? Must have been there for a reason.
3. I would have thought the louvers in most Roadster bonnet sides would have contributed greatly to getting rid of the hot air. Unfortunately my car doesn't have any - something I will need to address.

Cheers Robin

[AndrewKB]

Re: Overheating Roadster

I have no wish to appear facetious, but the key problem is the B-Series engine and cast exhaust manifold. Since I swopped my B-Series for a Ford Crossflow with a four branch steel pipe manifold (well-lagged), the over-heating problems have completely disappeared although the radiator is unchanged. I have fitted a 'low temp' thermostat (kicks in at 82F rather than 90F, if I recall correctly) but have rarely seen the temp gauge above the mid-point even after a thrashing on a trials section (with the electric fan on, admittedly). I'm afraid that overheating with the B-Series has been a problem ever since the first Marina-based Marlin.

[duncan]

Re: Overheating Roadster

If you have a clean "new" core then the radiator is plenty big enough

I have seen lots of issues with water systems over the years - but not with the air flow part

The original radiator has about twice the cooling needed for a "tuned" 1800cc B Series
Which does mean that if it's half clogged up you will be marginal

[Ye Ol Ripper]

Re: Overheating Roadster

I agree that speeding up the water pump shouldn’t cause extra stresses on it but wouldn’t that speed up the water flow through the radiator and therefore not cooling it enough before it enters the engine again.
Cheers, Martin.

This is an area that is not usual to explore as on competition cars, the usual route is to fit a radiator with larger surface area by it either having larger dimensions if there is space to do so or by adding extra cores.

With the Roadster a lot of heat accumulates in the engine bay and also at the back of the engine & transmission Tunnel area.

My idea is to try and move the water /heat around No 4 Cylinder back faster to the radiator area. No 4 has been known to distort on the bores even in MGB's, iirc something to do with the engine tilts back slightly and causes sediment to restrict the water flow.

With the Roadster moving, the water is cooled by colder air that passes through the radiator , if the pump is turning faster my theory is it might remove that heat in No4 faster.

If it wasn't for the heat accumulation at the back of the engine and transmission tunnel, this water pump pulley exchange is something that I would not normally consider.

If the heat could escape at the back of the engine by passing along the tunnel , then I totally agree having the water circulating in the radiator at a slower speed would be beneficial as it would have more time to cool.

The Roadster's heat accumulation phenomenon is unusual, so all avenues are worth exploring.

As this is unexplored territory, how beneficial this will be is currently unknown.

Every little bit helps and the lower you can get your engine temperature towards iirc 84/85 deg, then the more power it will produce and will be less susceptible to pinking as well.

It may or may not help ,but I do think its worth giving it a try, if a smaller pulley is readily available.

The water pumps flange will be the limiting factor on how small a pulley could be fitted. So I wouldn't expect that marginal speed change to cause cavitation on a B series.

If it doesn't work , it's an easy task to swap back to the correct water pump pulley.

[stevejgreen]

Re: Overheating Roadster

Further reading on cavitation. It’s a real thing.

https://oaktrust.library.tamu.edu/handle/1969.1/163898

[meverett]

Re: Overheating Roadster

I agree that speeding up the water pump shouldn’t cause extra stresses on it but wouldn’t that speed up the water flow through the radiator and therefore not cooling it enough before it enters the engine again.
Cheers, Martin.

[Ye Ol Ripper]

Re: Overheating Roadster

I have seen Mini A series engines rev to over 8k and the water pump has not disintegrated because of the speed of rotation. Infact, I have never seen a water pump fail or have cavitation issues , because of an increased rotational speed. That was whilst Dyno testing for over 20 years fully modified race engines producing 2-3 times the BHP that they produced in standard form.

So Steve where do you get that opinion from please?

Waterpumps fail due to:


1) The bearing seal failing first causing the bearing to rust and then you get play in it.
Same issue with washing machine drum bearings , that only rotate at 1200rpm.

2) the water pump or Washing machine drum is overloaded by over tightening the fan belt or in the case of the washing machine overloading the weight in the drum.

With a Roadster to solve problems or issues with it, we have to sometimes "think out of the box" and be innovative.

If Mr James Dyson didn't have that approach all vacuum cleaners and cooling fans would work and look alike.

Agreed there are examples of poorly constructed waterpumps , most of which have plastic impellor's that break from debris or some become loose on the shaft ( The 2.8 MA61 Toyota Supra's were famous for this , yet the dealers sited a head gasket failure - The cure was to replace the water pump).

There have been cases of impellor problems with the B series pump, but that will be age related as it has occurred on standard engines working in their designed rev ranges.

I do not envisage there being very large improvements by speeding up the water pump , but every little bit helps when there are limitations with space within the nose cone.

I have heard of people that had fitted Rover V8's in their Marlin's fitted an additional radiator under the nosecone, mounted horizontally. Apparently that worked.

[stevejgreen]

Re: Overheating Roadster

I note on the MGB /Marina water pump that there are extra bolt holes, so this got me wondering if there is another pulley for the water pump that holds the fan belt that is a slightly smaller diameter than the original.

If so, from another British car of that era, then the water pump would then turn faster for any given engine speed.

I haven't a clue whether it will help but certainly worth investigating.

Has anyone explored this avenue of thought?

A track through the parts lists, (guess where) might help, it’s an interesting avenue to investigate, but not for me.
Simply speeding up a pump does not necessarily increase the water flow, there is a complex pattern of cavitation that can rapidly destroy any perceived benefits, as well as the pump vanes.

[Ye Ol Ripper]

Re: Overheating Roadster

I note on the MGB /Marina water pump that there are extra bolt holes, so this got me wondering if there is another pulley for the water pump that holds the fan belt that is a slightly smaller diameter than the original.

If so, from another British car of that era, then the water pump would then turn faster for any given engine speed.

I haven't a clue whether it will help but certainly worth investigating.

Has anyone explored this avenue of thought?