14 replies to this topic

[tadleysimon]

ive been reading and there alot of conflicting advice. i have a 1275 metro engine with no bypass.

should i drill my thermostat?

and if yes, how many holes at what size?

cheers

[minimender]

If it's a Mini one it should have a hole in it.
If your heater is fed from below the thermostat (as in the Metro) then you wont need a hole in it.
If you really want one then drill a small hole in it by why would you?

[zebidee]

When replacing my thermostat on mine (A+ with no bypass and using standard mini thermostat housing) I noticed it didn't have any holes in it. It had been run like this for the whole time I had it (2 years by then) without any problems whatsoever! When I fitted the new thermostat I decided to drill holes just because I had heard it was unsafe to run without some form of bypass. I found the diameter of the standard bypass hose and was going to drill under that amount. I think I ended up doing 3 3mm holes (unfortunately I can't quite remember) which was far smaller in the end than the original bypass, and it takes a hell of a long time to get up to a good running temperature! When I do a bit of work on it over Christmas I'm going to put an undrilled stat back in!

Edited by zebidee, 15 December 2009 - 10:05 PM.

[mini13]

essentially the hole is to let through any air, a lot of stats with no holes have a "nick" at the opening edge so air can get through,

[zebidee]

essentially the hole is to let through any air, a lot of stats with no holes have a "nick" at the opening edge so air can get through,

I thought its main reason was to allow some flow of coolant around the head during the engine warming up to avoid hot spots

[Dan]

He means the standard hole, the one with a float valve fitted. The engine needs a bypass of some kind. If there is a chance for the pump to be running without coolant flowing the pump will be more likely to cavitate. The bypass won't make any real difference to warm up time if everything else is working and the bypass isn't excessive.

[CobraV8]

On older motors- they normally had a small bypass hose between the head and block. If this was removed and the holes blocked up, you needed some extra holes in the thermostat to allow the bypass of water flow. I dont know about the A+, but if they have ditched the hose, I am sure what is standard would be ok.

[zebidee]

He means the standard hole, the one with a float valve fitted. The engine needs a bypass of some kind. If there is a chance for the pump to be running without coolant flowing the pump will be more likely to cavitate. The bypass won't make any real difference to warm up time if everything else is working and the bypass isn't excessive.

Ah I see!

Well I can only say that the bypass was the only thing I had changed at that point, and it did take noticeably longer to get up to temperature. Nothing else was changed and nothing was wrong before

[Dan]

All A+ engines use a bypass as standard.

[il-barba]

i have the same problem of the car taking long to get up to temperature. i am blaming either of two things. it is either the thermostat is stuck open a little bit.

or another theory i have is that i have put the thermostat gasket the wrong way round, allowing coolant to flow from under the thermostat. what should go first, the thermostat or the gasket? or am i just building useless theories?

[Dan]

It is usually just a tired thermostat that opens too early. I don't understand what you mean about the gasket.

[tadleysimon]

i do and it goes thermostat into the head, gasket ontop, i highly doubt you got that wrong though because it doesnt look right the other way round

[bmcecosse]

If you want fast heater warm up - block off the bypass, and make 1 x 1/8" hole in the rim of the stat. Also - fit an 88 or even 92 degree thermostat - and make sure the heater valve is wide open!

[Ethel]

How do you know it's taking longer to warm up? Are you going off the temperature gauge? Its sensor is right under the stat and could be proving the point about a bypass ensuring good circulation and even temperatures.

[zebidee]

How do you know it's taking longer to warm up? Are you going off the temperature gauge? Its sensor is right under the stat and could be proving the point about a bypass ensuring good circulation and even temperatures.

Most excellent point!