Coolant Not Circulating

Samer

Well-known member
Jul 12, 2006
80
1
Washington DC
Putting this out there before I start figuring this out - incase a common issue:

Was driving my Discovery 1 up hill around a corner at about 3000 RMP when I noticed engine temp starting to rise. I pulled off before I was anywhere in the red. The coolant In the reservoir was boiling and I couldn't feel any pressure in the upper hose while motor was running - I figured my thermostat failed in the closed position.

Got home (keeping an eye on engine temp) and took off the thermostat housing. Thermostat was open and looked in good clean condition. I put the housing back without the thermostat and ran the engine. Still no pressure in the upper hose.

No strange noises come from the water pump and water in the reservoir is still getting very hot when running but no circulation. No obvious leaks. So I'm wondering:

1. Could the heater core be causing blockage? In that case would bypassing it be the way to diagnose this issue?

2. I would imagine if the radiator was blocked I would get full pressure on the top hose but none on the bottom - is that correct?

3. Would water pump failure create this situation because I would think it would fail by leaking or having a bearing fail but still push water as long as the pully was turning.

If anyone has encountered this before I would be glad to hear your thoughts.
Always appreciated.
 
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Samer

Well-known member
Jul 12, 2006
80
1
Washington DC
The more I research this the more I suspect I might just have a leak some in the system and losing pressure. Practically no coolant came out when I undid my top hose so I'll do a more thorough inspection tomorrow after filling and bleeding the system
 

Blue

Well-known member
Mar 26, 2004
9,418
473
AZ
If you’re leaking that much while driving at speed you should smell the sweet aroma Of coolant rising off the exhaust manifolds. This is typically a pleasure reserved for D2 owners.
 
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Swedjen2

Well-known member
Sep 12, 2018
556
113
California
Oh yeah, check the throttle body heater that is under the intake right in front of the throttle. There are two small (1/4"?) hoses, the feed and return lines that go to and from the overflow tank you can follow to the heater unit. They are a known leak point. You can get a nice, thick brass replacement from a shop in Canada, or pay more for another similar product from a shop in either Somewhere, Arizona or Walter White's old town - ABQ.
And, the tank itself. The PRC made tank is below standards and the small hose nipples can crack at the point they join the tank. A hairline leak only obvious after the tank is empty, the temp. gage is pegged and you've reached Destination F*cked.
What else?
The water pump gasket. Poor installation.
The ultra-goofy 3-way plastic tee and bleed screw just aft of the radiator -it's looking you in the face when you open the hood. Get an aluminum replacement off Amazon.
The goofy plastic 3-way thermostat about half-way down the passenger side of the radiator. Get a 180 degree thermostat. regardless.
And to top it off, the head gaskets. There are whole libraries in The Mechanicum that owe their existence to Rover head gasket leaks.

How old is your radiator? I'd start there and if it's more than 5 years old and has the plastic side tanks, get a new one. 1 leak point down, 8 or 9 to go.

Praise the Omnissiah after each repair to ensure it stays fixed. You can look it up.
 
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Samer

Well-known member
Jul 12, 2006
80
1
Washington DC
Thanks for that great summary. I think the 3-way connector is a Disco 2 item but everything else is also relevant to my truck.

What happened to me, much like you describe, is coolant loss from the seam between the two halves of the original (black) coolant reservoir that only revealed itself after getting home (Driving while watching the temp and stopping to let the engine cool).

I initially thought it was a bad thermostat because the coolant was low but not empty in the tank.

But after refilling and getting the engine up to temp. I could see a slow leak between the tank and the mounting bracket (had to use an inspection mirror).

Now that I’ve pinned down the first leak I can chase through the rest of the points you mentioned as I change out hoses, flush and refresh. Good to know metal substitutes out there for the plastic OE parts.

Thanks for all that useful information.
 
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Samer

Well-known member
Jul 12, 2006
80
1
Washington DC
F21EBA83-8057-44CD-8C17-93E0D04669C9.jpeg
Just posting the location of my coolant tank leak for reference in case someone runs into this slow leak scenario on a factory black tank - this seam is typically hidden from view when installed and would only open up In a heated over pressurized situation slowly bleeding away coolant. Luckily I caught The needle moving up quickly before any engine overheating