I bought my 91 convertible for a song and a dance, even with my voice, because it would lose coolant and overheat in traffic. So here's what I've found so far.
Somewhere in the past the engine driven fan went away, replaced by a 16" electric in the top right corner of the radiator, no shrouds, and turned on and off by a thermostat jammed into the top row of fins at the "A" head inlet. The stock electric fan was still there.
The heater core was bypassed by putting one of those radiator flush fittings between the inlet and outlet hose.
The space between the radiator and condenser was 2/3 filled with leaves and other wind blown debris.
Now this:
You are seeing it as I found it. "A" side thermostat housing with a broken bolt, with the bolt head glued back in with red gasket maker, and no thermostat.
What I understand from reading around here, no thermostat is a bad thing.
So I am not sure how this wound up like this, I hesitate to blame the mechanic this car was taken to, but I am pretty sure the fellow that owned it didn't do any of his own work beyond keeping the fluids topped off.

Near as I can tell, somebody spent what appears to be a fair amount of money chasing a problem that would have been fixed by simply cleaning the leaves out from in front of the radiator. The electric fan was in the wrong place for the lack of thermostat (it cooled the top third of the radiator, the "b" side), the switch to turn on the fan was in the wrong place to sense the increased temp from lack of thermostat, if the cabin heat control was anything other than "off" the coolant from the head ran directly to the intake of the pump, bypassing the radiator. I dunno that this thing had any choice but to overheat.

My prayer now is that it didn't get hot enough to drop a valve seat.

and since I'm in it this far, change the water pump?

So there you go. Sometimes things really are that simple.

Steve aka 71 MKIV

91 XJS convertible classic edition
71 Triumph Spitfire
"never underestimate the perversity of an inanimate object."

 

At this juncture I'd replace the water pump if it was noisy or leaking. Look at the underside of the pump for coolant stains. Otherwise, no.

IMO the effort and money is best allocated for removing the radiator for professional cleaning at a radiator shop. It's common for them to be clogged up internally. Sometimes a new core is needed.

If you DO decide to replace the water pump then the time to do it is when the radiator is out.

If the heater is bypassed then I suspect the heater core is leaking. Fortunately, your car has the later system and replacement is not particularly gruesome.

Cheers
DD

 

What are you going to do about the electric fan? That mechanical one does the heavy lifting, and if it's the replacement electric is not up to scratch, it'll still overheat in traffic. Only the best electric fans can replace the big mechanically driven one, and do an adequate job, and probably only if you replace both (two decent electric fans being equal to one big mechanical one plus the one crap stock electric one).

 

yeah, no stat is usually pretty bad. It works in some cars, but not in most. The slot at wide open for the Tstat is much smaller than the housing itself. Not to mention it disrupts flow as well. If the coolant moves too fast, it can't really absorb heat, likewise there isn't much time for the radiator to take heat away.

Like mark said the mechanical fan does a lot of work and usually isn't worth replacing with electric for the money. Sounds like it would be easiest to go back to stock with the housing, fan, and anything else because baseline from the factory clearly is not an overheating condition.

 

I have the radiator out, so I will most likely do something with the pump, probably rebuild it myself.

The radiator will be going out for a cleaning and rodding.

Gotta snouse around and see if I can find a donor car for the fan, bearing housing and shroud. Otherwise I would probably go for some sort of variable speed twin fan in some sort of shroud that covers the whole radiator. Something like this:

https://www.flex-a-lite.com/reversib...ontroller.html

a pressure test of the heater core is on the list of projects to do in the near future.

The archaeology is sometimes the hardest part.

Steve aka 71MKIV
91 XJS convertible classic edition
71 Triumph Spitfire
A 20 minute project is never more than one broken bolt away from a 3 day ordeal.

 

No thermostat in a bypass cooling system will have coolant bypassing the radiator and circulating uncooled back through the motor - not a good thing.

I would not source a used mechanical fan, there is no guarantee that the clutch will be good. Buy new or install eFans properly.

 

Well, the used bits would be the bearing housing and the belt tensioner, I would use a new fan and new clutch.

 

I've not tried it. But, a way to check a heater core for leaks in situ might be a vacuum test. A Mitty Vac tool would be ideal. Pump it down to 15 psi or so. See if it holds. Same technique as the AC pros use... They do have more sophisticated tools, but the idea is the same.


Carl

 

Thanks Carl, I have a Mity Vac, and enough misc to make an adapter. So we shall see.

There's lots to do.

Steve 91 Jaguar XJS convertible classic edition
71 Triumph Spitfire
Every 20 minute project is one broken bolt away from a 3 day ordeal.