4.2 in a Mk2: Water pump?

For those of you that put a 4.2 in your Mk2, which water pump did you use?

I have a MkX 4.2 and I can buy a new E-type pump for the cost of rebuilding a MkX pump. Does it matter which pump? Does one mate up better to the Mk2 radiator?

I used the MK2 pump on the front of my 1975 3.4 XJ6 Engine , in my 240 , the MK2 pump Impeller is a few mm smaller , but I have had no heating issues !
I do have a uprated Rad core !

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Yes it matters because the outlets from the pumps changed over the years, and the incorrect one for your radiator will cause big headaches

Tony, can you elaborate? Is it the sizing or the angle or something else? I don’t think anything else will fit, so I assume I’ll end up with an aftermarket aluminum MK2 radiator or a recored original. I don’t have a radiator right now.

So you’re saying I need a MK2 3.8 pump, and that it will fit the 4.2 timing cover?

Also, the Mk2 pump has 2 outlets whereas the MkX only has 1. Where does the smaller pipe go on a Mk2… or rather, where would it go on a MkX 4.2?

There is main 3 issues

  • What size, number and orientation of pipes are on your MK2 Radiator

  • will that match up with the WP you propose to use

  • will a 3.8 MK2 WP fit a 4.2 MX engine

Dealing with the last one first, if you have the original 3.8 WP, you can check

Otherwise I would check the Parts Manuals of the major suppliers, they have diagrams

I can say for sure there was at least 4 iterations of MKX radiator/WP, and not easily compatible, as the inlet and out let pipes were altered for rad and heater

You can usually plumb up a water pump to work with adaptors, but a perfect match is ideal

My Mk2 came without a radiator or engine. The 4.2 came without a radiator, so I’m flying blind without much to go on for comparisons. The major suppliers list one WP for all Mk2s and only 1 radiator that I see. From the diagrams, the MK2 pump goes straight down and the MkX is at an angle, and then a series of pipes and hoses pieced together. Very different radiators.
It seems like the 4.2 swap is common enough that there would be a common solution. I just don’t want to spend a lot of time reinventing the wheel.

Well you know you must obtain a MK2 radiator, so if you are not in a hurry, I would buy that and see if everything will fit ok.

Note the steel bent pipes to hook up the MKX parts.
That is the mid-iteration of the MKX cooling systems

My personal opinion is fitting a MK2 WP to a MK2 with a MK2 rad would be the most straightforward (Ian said he did this)

Are MK2 WPs not readily available new or rebuilt ?

Also worth checking the archives, as others have done it before

The gasket part number may help tell if they are the same