MGB - coolant pump replacement (Part 1)

Last Fall, before I got too deep into fixing things on the MG, I took it to the specialists at British Auto NorthWest in North Plains. After addressing just about everything else, I am finally getting to the most important thing they called out: the coolant pump. Today's post covers that effort. This got really long, so I've split it into pieces. So, today we'll cover parts and the tear down.

Parts
Like any project, replacement parts are needed. At the very least, we need a new pump. These pumps aren't nearly as expensive as you may fear: $40US. These usually deliver with a replacement gasket. Verify before you commit.

Hoses. How old are your hoses? You don't know? Well, they're probably really old then. Best to assume that anyway. The hoses to/from the heater and the larger ones to/from the radiator are car-specific. Again, they are not terribly expensive unless you choose to go with silicone. Even then, the set is around $60US. The other hoses (from rear of head to pipe, and the smaller ones connected to the overflow bottle) are standard 5/16" hoses and can be purchased by the foot for next to nothing.

Hose Clamps. Look at the hose clamps. Rusty like mine? Get a slew of new ones. You'll need 4 larger ones for the hoses which route to the radiator. There are 4 smaller ones for the hoses leading to/from the heater plus 2 more smaller ones for the hose leading from the rear of the head, 2 more for the smaller hose from the radiator to the overflow bottle and one extra for the overflow bottle overflow hose. The other end of that hose on my MGB routed through the radiator mount, which seemed kinda weird. I'm not sure where it's supposed to go, but it probably doesn't need a clamp on that end. I found all clamps at Ace Hardware and they cost around $1US a-piece, so around $15US all-in.

Thermostat. If you haven't had any temperature issues, you probably don't need to change it. They are very inexpensive though, and getting the system apart for a thermostat afterwards just seems needless. So, I encourage spending the extra $8. I also replaced the thermostat housing ($6US), because mine was rusty and I replaced the housing gasket ($1US). The gasket does not ship with the housing, so buy them both. You may find it necessary to change the gasket even if you aren't swapping out the housing. My original gasket was smashed up against the housing and didn't look reusable. Often things like this are one-use-only. Also note that the housing does not deliver with the filler plug in the top. For a small brass cap, this is actually kind of expensive relative to everything else at $4.50US.

Temperature Sender. If your engine temp gauge isn't working, now would be the time to replace it. My gauge worked fine, so I didn't do this. They are around $7US, so in retrospect, I probably should have.

Fan Relay Switch. If your radiator fans are still triggered by the sensor in the radiator, you may want to replace this while you're in there. These range from $15US to $40US, representing the most expensive part so far. My fans are activated by a switch on the dash so I didn't need this. I highly recommend the dash switch. From talking to the British Auto Works guys, it sounds like those thermostatic fan switches are the system weak spot.

Fasteners. Of course I'm going to advocate replacing all fasteners. The thermostat housing is held on with 3 studs. These are 5/16-18 on the head-side and 5/16-24 pointing up. All of the bolts I replaced are 5/16-24 as well, just different lengths. I did not replace the tensioner bolt for the alternator, but did replace the 2 mounting bolts, the studs and nuts for the thermostat housing and the bolts for the coolant pump. Get stainless, if you can, so they don't rust-up on you again. And, they look pretty.

Tear Down
I was fortunate to have my step-son K2 available to help out again. So, while I finished routing and re-routing the fuel lines, fuel filter, flip-over shut-off valve, etc, he started the cooling system tear down. We had pushed the MG back into the garage for the Fall, with fears of the rainy season starting before we had a top. Our fears were met with sheeting rain on the other side of the garage door transom. Since we're dealing with old-skool coolant that animals like to drink (and then die from), it was all the more important to keep the cat out of the garage and the liquids well contained. Since I was working on the fuel system at the other end, we decided not to lift the front end, and used a dishpan to catch coolant.

K2 attacked the lower radiator hose from above, loosening the rusty clamp and then pulling off the hose from the lower radiator bib. Once the gush slowed to a trickle, he removed the cap from the overflow bottle. This allowed air into the system and more coolant came out. The coolant up to this point was really nice and green. I'd expected much worse. We poured the coolant into an empty coolant bottle for re-use and then returned to the job of removing hoses. Some of the hose clamps were very rusty. We used a WD-40 product for rust penetration to loosen them up. It worked for all but one which needed to get cut off.

old rusty pump on its way out

With the hoses off, and the coolant stowed away, we moved on to removing the coolant pump. After doing the work, I found a step-by-step on the MG experience forum, but I'll detail what we did... which, of course, wasn't what they had written down. First, we loosened the mounting and tensioner bolts for the alternator. These are 1/2" bolts. We released the tension on the belt and pulled the belt. We noted that the coolant pump shares one of the bolts with the alternator so we pulled both mounting bolts completely and moved the alternator out of the way. Now, we could get after the coolant pump. The pulley is reusable and the four bolts holding it to the pulley loosened by hand. I held the pulley with one hand and a small socket ratchet in the other. I still had the smog pump pulley, so in order of removal they go: bolts, pulley cap, smog pulley, accessory pulley. I set the cap and accessory pulley aside for clean-up. Once the pulleys were off, I could get after the coolant pump, using our 1/2" socket again. We were reminded of gravity as we loosened the last bolt and coolant started to flow from behind the pump. Considering how far we'd gone, this was our first spill.

We set the pump aside and shifted to the thermostat housing. The rust on the studs and the nuts on top was so bad that all three studs spooled out of the head rather than the nut threading off. The gasket was a mess and the thermostat was stuck to the head. Some quick work with a putty knife removed both. Last, I removed the overflow bottle by removing the 2 nuts from inside the passenger-side fender/wing and we were ready to clean some stuff up.

That's it for today's portion of this work. Next time, I'll cover cleaning up various parts, including the inside of the radiator, and re-assembly. Thanks, as always, for following along.