If your crack was in the mounting hole like mine was, then the RTV might do the trick. I squirted it in with the system full of coolant and it held just great. But with how quickly these engines are destroyed by low coolant, I wanted to get the cracked radiator out and a new one in on my schedule. Looking at how well it sealed up with the RTV makes me think it could last a while, but with the tank expanding and contracting with every use of the vehicle, I would be worried that the little crack would be a much bigger crack in no time. I used Permatex Ultra Copper which supposedly has the best adhesion to oily surfaces but I'm not sure if that really made a difference.

If your problem is the broken bleed line nipple, then use bolts and clamps as a temporary fix but that line is the bleed hose that dumps excess fluid in the system into the expansion tank when the coolant gets hot and expands.

 

Well, on the advice of Savannah I back-flushed the heater core last night. I pulled the heater hoses off at the tubes from the pump and the intake and hokked a length of 3/4 inch heater hose to the inlet. For anyone else doing this job, you can use 1/2 inch pvc pipe to couple the factory heater hose to a 3/4 inch hose so you can direct the flow to a bucket. I have a hose nozzle that has a tapered brass outlet that fit into the outlet hose so that part was easy. I was able to hook the hose to my hot water, so I figured some heat couldn't hurt. I slowly opened the nozzle letting the water flow backwards and it pretty much trickled out the other end. I kept adding some flow until the hose firmed up, then all of a sudden it let go and the water came blowing out the other end. It let go so suddenly that I thought I popped the core. After that, I was able to run the hose wide open. The only thing I found in the discharge water was some yellowy-white stuff floating on the surface. Wierd. I was expecting orange sludge.

After that I blew the water out using a shop-vac on the blower side, then filled it with distilled water and blew that out two times. I filled it with 50/50 coolant, hooked up the lines, bled the system and fired it up. Best heat I ever got out of that thing. More heat at idle then I had on the highway before. The engine temp at idle is now down around 190 instead of 197. All I can say is thanks for the suggestion and for anyone changing coolant, make sure you backflush the heater core no matter how clean the coolant comes out. I don't know what was blocking mine but it definitely was doing a very good job.

 

It was in fact the mounting hole like yours. I used the RTV, then a Flat Fiber Rubber Washer between the radiator and shroud. I'm hoping that holds. I'll keep a close eye on it and report back if it ends up giving up.

 

what brand of thermostat would you recommend and where do I get it? Thanks for any help!

 

There are a few ways to go with the thermostat. The factory one is called a 190 degree thermostat, but it only starts to open at 190 so the engine runs much hotter than that, like 210 to 220. The consensus seems to be that the Rover V8 should not be allowed to run this hot. Most people seem to be switching over to a 180 degree thermostat. I'm running a Motorad 180, which is an aftermarket supplier. The other option is a gray Rover thermostat that also is a 180 degree.

The Discovery 2 thermostat is somewhat unique in that it has a built in by-pass valve to divert most of the coolant flow to the heater core at idle, but then opens up as the coolant flow increases when the engine rpm increases. This valve is controlled by a spring. In the Motorad, the spring rate is the same as it is in the OEM 190. The gray Rover one is designed for the diesel engine which idles at a lower rpm than the gas engine so the bypass spring is softer. This likely allows some of the coolant to bypass the ehater core at idle, so there may not be as much heat. However, Motorad has a somewhat spotty quality record so some people avoid their thermostats. I've had no issues with mine, although when I just flushed my system, I looked inthe thermostat and saw that the seal around the thermostat in the housing was partially displaced. This could cause the coolant to bypass the thermostat so it will only make the engine run cooler if it affects it at all, but I'll be replacing it just the same. The Motorad part number is 439-180, the Rover number is PEL500110. You can get the Rover one from Lucky8 or BP Utah. The Motorad is available through other suppliers. I got mine from Amazon.

 

re: thermostat is somewhat unique in that it has a built in by-pass valve -

Also found in lots of other vehicles, from Mercedes to some Fords, even pickups. IMHO the shift from a 180 stat in earlier Rovers (fully open at 180) to fully open at 204, plus remote mounting adding some delay, plus smaller radiator (compared to D1), put the D2 owners at a disadvantage. Add the "who knows what temp it is" gauge, and it is no wonder problems result. Most guys would not drive their truck around all the time at 227F - if they knew it was happening.

 

Good to know. I had never seen a setup like the one that Rover uses before. Do other manufacturers use the crazy housing too, or do they just mount a similar thermostat in the head or manifold?

So the way the Discovery 2 thermostat works is one of the top lines connects to the outlet from the block and to the top of the radiator, and the other goes to the inlet on the water pump. The heater core inlet basically comes from the block and the core outlet tee's into the hose going from the thermostat to the pump. The water pump pressurizes the coolant in the block. When the truck is idling, the coolant flowing from the block to the thermostat is stopped by the disk held closed by the bypass spring so the flow instead goes through the heater core and back to the pump inlet. This leaves the section of hose running from the thermostat to the point where the heater core outlet tee's into the hose much cooler than the coolant in the block. To allow the thermostat to know what the temperature in the engine is, the bypass disk has sensor holes in it that allow some of the hot coolant in the other hose on the top of the thermostat to dribble in and heat up the chamber that houses the actual thermostat. When the engine is operating at higher rpm's, the bypass valve opens due to the higher pressure from faster spinning the water pump and the hot coolant flows through the upper chamber, out through the other hose and back to the pump. Once the thermostat opens, the coolant flows into the bottom of the thermostat housing and out to the hose that goes back to the pump. The pressure of the flowing coolant combined with the spring on the bypass disk keeps the bypass valve closed. This allows the coolant to flow through the radiator essentially bypassing the section of hose that runs to the other port on top of the thermostat.

With the softer spring, the coolant likely flows through the top chamber at idle so the thermostat likely responds quicker to the engine heat but once you are underway, there shouldn't be a difference because bypass valve has already opened, right?

 

Not quite. The stat has two springs. At cold idle, main stat is not open yet. WP pressure not enough to force open the sample disc. Revved up, sample disc opens, freshly warmed water enters the cavity and back out to WP and heater. Faster heat in the morning. When the main stat opens, it pushed the sample disc back up closed, and at that point only sample flow of hot water is getting mixed in the cavity. So if those four little holes get plugged, it changes point at which stat operates.

On some trucks this stat is in the intake manifold. On a Merc they are in a housing that is part of the water pump.

 

Now I'm confused. Isn't the upper "mixing" chamber also where the coolant flows? When hot, the thermostat opens and the coolant flows in from the lower inlet from the radiator, through the thermostat and into the upper chamber. Since the bypass disk is forced shut, the coolant flows out the port leading to the pump while the other thermostat inlet no longer flows. This puts the reactive side of the thermostat in the flow of the coolant coming from the radiator, correct? I should think that with this setup, there is no way to get the running temps down to the same number as the thermostat because it will sort of be reacting to an average of the hot coolant on the radiator inlet side and the colder coolant on the radiator inlet side. When the thermostat is closed it reads temps in the chamber from the engine inlet and when open it reads temps from the radiator outlet.

 

Examine the cutaway pix. It is the orientation as installed. The housing is double walled. The sample hole disk is at the top. Water flows thru holes, circulates in the chamber with rad water (cooler) and passes out thru the slots in the chamber walls to the space between the chamber and the outer wall, and out the "side arm" port and off to the water pump and cirulation thru the heater core and throttle body heater.

When main stat is closed, and engine rpm comes above idle, the soft spring of the sample disk allows it to descend, more flow of warm water thru to heater core, etc.

When main stat finally warms up, it opens upward, and the soft spring of the the sample disk is forced to the closed position. The main stat may move partial to full open, like a variable speed drill, not a light switch.

Regadless of main stat position, there is always some water flow thru to water pump, and there is always some sample water coming in from the holes in the sample disk. What a delicate dance we have here, plug up some of those holes with trash, and performance of the heating chamber is slowed, while engine block heats higher. The sample holes are arranged to be at the bottom of a hose from the T fitting, so they become a natural collection spot for crud.

The flow thru the stat body is cool water in the bottom, out the side to water pump, and hot water for sample comes in the top, and mre hot water if needed during warm up operation, and out the side. See attached flow chart from the RAVE.

I'm sure it made more sense in the original Klingon. Just add Dexcool for a really long life reliable system.... almost like it was designed to fail between expiration of warranty and last loan payment (what's new about that?)...

Could holes be enlarged slightly for lower temp or more consistent temp? Wind chill in winter must change the temp of the housing. Could you wrap it with insulating foam tape and get more consistent operation?