36 replies to this topic

[matt050990]

Hey all

Going to get a new water pump while I'm swapping engines.

Seen 2 types online so need people's advice.....

With bypass
Or without bypass

What's the difference and what's the pro's and con's of both.

If it makes any difference it's going on a 1275 A+ engine.


Much ta
Matt

[blackbelt1990]

You need to know whether you've got a cylinder head with a bypass or not. I know my A+ 1275 has a bypass and I don't know when the changeover year was.

[Cooperman]

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.
You might want to drill a few 5 mm holes around the edge of the thermostat to allow a bit of flow before the stat opens.

[Spider]

I fit the blanks off ones and while many also drill a few holes in the T'stat, I have never bothered. The only down side of doing this is it take a few mins longer to fill the cooling system, otherwise the T'stat is left alone to perform it's job.

[Tahiti Joe]

I run a by-pass head and pump, use a silicon hose for the bypass hose if you do, not one of them flexi pieces of crap. Never had an issue. *touches wood*

[RooBoonix]

I fit the blanks off ones and while many also drill a few holes in the T'stat, I have never bothered. The only down side of doing this is it take a few mins longer to fill the cooling system, otherwise the T'stat is left alone to perform it's job.

Ive read that due to no flow it could lead to hot spots in the block and head if you do this?

Edited by RooBoonix, 19 June 2015 - 07:58 PM.

[nicklouse]

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.You might want to drill a few 5 mm holes around the edge of the thermostat to allow a bit of flow before the stat opens.

That is what I always run.

[blackbelt1990]

I run a by-pass head and pump, use a silicon hose for the bypass hose if you do, not one of them flexi pieces of crap. Never had an issue. *touches wood*

Same here, always fit a silicone one and never had a problem!

[Dan]

A series engines (in fact most engines) need a bypass of some sort. In all standard systems where the bypass hose is not used there is a different bypass in another area. What the bypass is actually bypassing is the rad of course as well as the stat, allowing the pump to draw a little heated coolant down from the head. This heats the coolant faster, and also allows the pump to actually work. If the pump cannot draw from anywhere then it will cavitate. This creates hot spots around cylinder 1 and erodes both the cylinder wall and pump impeller. Hot spots also develop in the head. Drilling the stat allows some coolant to flow which gives the pump something to draw on but does not bypass the rad, lengthening warm up time. The bypass hose also stops cylinder 1 being inundated with very cold water direct from the rad by mixing in a bit of warm water, reducing the temperatrue gradient across the block. If you don't want to use the bypass hose, arrange a different bypass using a heated manifold or something like Rover did.

[matt050990]

Hmmmm so very strong recommendations from both sides.

I'll have a look when I'm in the garage next to see if my head has a bypass or not.

I'm guessing both are just as good at keeping temp low?

[Dan]

I believe I've read something about engines without a bypass running less consistant temperatures as the stat tends to cycle between open and closed. Not too cool or too hot, just not consitant.

[matt050990]

I think I'll go for the with bypass route.
Don't fancy driving holes and stuff as knowing me I'll break it!

Thanks for all the replies lads,

[blackbelt1990]

I think I'll go for the with bypass route.
Don't fancy driving holes and stuff as knowing me I'll break it!

Thanks for all the replies lads,

Just use one of these, I've never known one break!

http://www.minispare...|Back to search

[matt050990]

I think I'll go for the with bypass route.
Don't fancy driving holes and stuff as knowing me I'll break it!
Thanks for all the replies lads,

Just use one of these, I've never known one break!http://www.minispare...|Back to search

Was looking at that exact one last night mate. Matches the rest of my blue silicone!

[Spider]

I believe I've read something about engines without a bypass running less consistant temperatures as the stat tends to cycle between open and closed. Not too cool or too hot, just not consitant.

 

Not if the T'stat is working properly. The T'stats are not Open OR Closed, they 'throttle' the flow to maintain a fairly constant temp.

 

All I'll say is I've been blanking them off and not drilling the T'stat for around 30 years, also built many engines this way too, never had an issue.