36 replies to this topic

[Spider]

 If the pump cannot draw from anywhere then it will cavitate.

 

They are a Centrifugal Pump Design. That style of Pump is in fact designed to be 'shut off' in that way so that they don't cavitate.

 

It has been proven that the original Head to pump by-pass causes cavitation, this comes about (so I have been told by a pump designer / tester) because the By-pass is much too close to the pump impeller. This is why Rover eventually changed the design of this set up.

[blacktulip]

as you are looking to run a performance engine i say stick with the bypass as minis without can create hot spots. This is on standard engines so this will increase on a performance engine.

[Dan]

The stat is meant to throttle yes, but without any bypass it doesn't do it well. The throttling range (so to speak) increases, someone posted test data about this on here a while back. I think it's to do with the response time of the wax capsule compared against the flow speed varying with engine speed.

So the cavitation on earlier engines would be caused by turbulence in the incoming flow? I can understand that but I thought the cavitation problems of A series engines were completely solved by simply slowing the pump with the A plus. I have seen some pretty seriously eroded impellers! I thought Rover deleted the head bypass port simply so that they could incorporate a permanant heated manifold without dramatically increasing the bypass volume.

[Spider]

Without a Bypass the T'stat can throttle from No Flow to Full Flow, so it can control the temp in a more stable and better way than if some of the flow by-passes the T'stat as that portion of the flow the T'stat has no control over, so in regards to claimed 'hot spots' it is more likely to occur with a by pass than without, though with or without, hot spots won't occur because of any perceived flow , more like because of turbulence or blocked flow paths.

 

Yes, too high a spinning impeller will also cause cavitation, however the impeller size used on these engines is small enough that they can be spun up to to fairly high speeds before cavitation occurs (I think my Pump friend said 5 800 - 6 000 shaft RPMs - without the bypass and pressurised to 0.8 bar), the by-pass while increasing the on-set of cavitation, isn't the only cause of it. The A plus engines we got out here were all fitted with the same size pulley as the earlier engines, in fact, I have been looking for the bigger pulleys but can't find one! They are very rare in these parts. The bigger pulley was fitted mainly to reduce noise as this was an issue in some of the European Markets. One other item that great reduces the likely hood of Cavitation is having a true Header Tank, so that the major part of the system is devoid of air.

 

To the guys who want to say this causes hot spot and other things, I have tried systems with, without and also 'part' (ie drilled T'stat) By-pass. Without doubt, I have found that a by-pass less system on these engines the way to go - hands down. If you haven't tried it, in a proper way  and test method, then please don't knock it.

Edited by Moke Spider, 20 June 2015 - 10:38 AM.

[1984mini25]

Best to get the one without the by-pass. Then blank off the head if the by-pass stub is there. Those by-pass hoses are a source of unreliability.
 

 

I've always used a short section of 1/2" heater hose and decent jubilee clips on all the minis I've owned/worked on for the bypass hose. I've never had a bypass hose fail, even on the trashed daily mini of the last 10 years.

 

Now if you chose to use those easy fit cheap rubber concertina type bypass hoses with rubbish clips, then you're just asking for it to fail.

[Fast Ivan]

I won't be using the bypass on my build

[dave1010]

The main reason for drilling a hole in the stat was to make sure there wasn't an air lock behind it, as this would cause it to overheat due to not having hot water touching it thus opening it. It was something we done on all stat changes when I was a mechanic back in the 70's and 80's .

[MrBounce]

I have done it the following way since the early nineties:

 

If you have a bypass hose and need to change the waterpump, simply use a bit of 1/2" heater hose and decent jubilee clips with hex screws. Never had one fail.

Edited by MrBounce, 20 June 2015 - 03:59 PM.

[mingy]

I have done it the following way since the early nineties:

 

If you have a bypass hose and need to change the waterpump, simply use a bit of 1/2" heater hose and decent jubilee clips with hex screws. Never had one fail.

Agree on this one, i have done the same with no problems. 

[nicklouse]

The main reason for drilling a hole in the stat was to make sure there wasn't an air lock behind it, as this would cause it to overheat due to not having hot water touching it thus opening it. It was something we done on all stat changes when I was a mechanic back in the 70's and 80's .

But they have that hole in as standard with a wiggly thing in it.

[blacktulip]

 

The main reason for drilling a hole in the stat was to make sure there wasn't an air lock behind it, as this would cause it to overheat due to not having hot water touching it thus opening it. It was something we done on all stat changes when I was a mechanic back in the 70's and 80's .

But they have that hole in as standard with a wiggly thing in it.

 

yeah whats that wiggly thing all about?

[dave1010]

The main reason for drilling a hole in the stat was to make sure there wasn't an air lock behind it, as this would cause it to overheat due to not having hot water touching it thus opening it. It was something we done on all stat changes when I was a mechanic back in the 70's and 80's .

But they have that hole in as standard with a wiggly thing in it.

not all stats had a jiggler but due to having issues with air blocks it was a done thing with every stat on any car of the day. The wiggly thing was supposed to keep the hole clear to help cut down on the air lock.

Edited by dave1010, 20 June 2015 - 09:48 PM.

[nicklouse]

Every one that I have ever bought have had one since the mid 80s.

[A-Cell]

The wiggly thing in thermostats is another version of the infamous Jiggle Pin, used to keep the hole clear. The same function as the one in the bottom of the flywheel and clutch housing.

[A-Cell]

The hole in the stat is to prevent air locks when filling with coolant.