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Discussion Starter #1
Continuing to have coolant issues and would like your suggestions for next steps to diagnose my issue:

Just replaced HG and inspected (visual) liner/blocks. All seemed to go okay (thanks for the help). Didn't see any visual evidence of slipped liner or cracked block. HG that I took out didn't appear (to me) to be in bad condition (no obvious cracks).

Got the P38 back together and went through coolant refill process. While running the engine with coolant reservoir cap off, the resovoir will overflow when the engine gets up to temp. (When the thermostat opens up I believe).

My observations:
  • Did compression test after getting HG back together. Readings seem to be consistent to me. There were 2 cylinders that were right around 150. All others were 155-160. I didn't see that as much of a variation/issue- am I wrong?
  • Might be wrong here but when I feel the hose below the thermostat as compared to above it (after the car has run for a while), the lower hose seems to be warm, but certainly cooler than the upper hose. Thermostat issue?
  • Heater hoses- appear to be the same temperature (to touch)
  • Have replaced reservoir cap a while ago
Possible issues:
  • Blocked radiator?
  • Thermostat issue?
  • Have not done a leak down test- should I? Would need to purchase the gauge.
Why do you all think my coolant is overflowing when I try to bleed the system?
 

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I am still learning the rope with my P 38 but I would wonder how old is the thermostat? since you are draining anyways pop the rad out and make sure it is not blocked, put in a new thermostat, that is of course if you rule out a crack in the block, ? I am sure someone will offer better advice , lol
 

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You haven't got rid of all the air so as it gets hot the air expands far more than coolant would and pushes the coolant out. If you can squeeze the top hose and hear coolant gurgling around in the system, there's still air in there.
 

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Discussion Starter #4
Thanks, Richard. You’ve been right with most of my issues. On this one, I’ve tried to bleed air out and read on different processes, including rave of course, till I’m blue in the face (I think you or someone else mentioned this Starting maybe a year ago). Given where I’m at (engine full of coolant and air in the system), which process to relieve entrapped air would you recommend? Rave?
 

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Another simple possibility I can think of is that you're taking too long to get the air pockets out. If the expansion tank cap is off when the engine is up to temp, the cooling system will not run properly. The cooling system has to operate under pressure, decreasing the boiling temperature of the coolant.
 

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My method is to remove the header tank cap, disconnect the bleed hose from the top of the radiator (carefully, without breaking the nipple off) and poke a bit of wire in to ensure the bleed path is clear. Blow down the pipe to make sure that is also clear and the inlet from it into the header tank neck is also clear. Fill the header tank to the top, squeeze the top hose, put finger over the bleed nipple and release the top hose. Keep doing that and keep topping up the header tank. What you are doing is blowing air out the bleed nipple when you squeeze the hose and sucking cooolant into the system when you release it. Once coolant starts to come out of the bleed nipple, put the hose back on. Carry on doing the squeeze, release process only now plug the hole inside the top of the header tank filler neck. When you reach the point where coolant comes into the header tank in a continuous stream, you should have done the job but if you can still hear gurgling in the cooling system, keep going, you haven't got all of the air out. Only when you can no longer hear any gurgling, start the engine and look for a continuous stream of coolant going back into the header tank through the small hole. If the hole in the radiator nipple, the hose or the hole into the header tank neck are blocked, you will never get all the air out.
 

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Discussion Starter #7
Thanks. I did that process. Twice actually. 2nd time drained/refilled (just through radiator drain plug). Both times, the radiator to header tank hose flowed strong for about 15-30 seconds. Then it would flow to a drip, very small stream (flowing down edge of tank) or even nothing at all. Then boil...

Upon 2nd fill, the reservoir was very slow to drain. Even when I first started putting coolant back in.
 

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Sounds like you've got some crud floating around in there that is blocking the bleed path. If any air can't bleed out through that hose then you won't get all the air out, it must run clear all the time. The crud will be at the top of the radiator so draining it from the bottom won't get it out. If you take both top and bottom hoses off and cobble together some reducers so you can put a hosepipe into the bottom, you'll backflush it and get anything in the top of the radiator out.
 

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Discussion Starter #9
I must admit, I lost my patience after this one! ha!

removed rad. backflushed. looked inside rad and didn't see gunk (from what little you can see from up/lower ports). looked clean. refilled per instructions. then:

no coolant stream from rad to header tank and boil after a few minutes.

Any other suggestions?
 

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It's possible to connect the smaller/ upper hoses the wrong way round on the thermostat apparently - which will screw up proceedings big time. You may also want to take the t/stat off anyway and test it with boiling water (add cold until it shuts, or drop the housing into a pan and bring it to the boil). But no coolant stream from the radiator is feeling like the water pump's not doing the biz.
On mine the PO had managed to install an EXTRA thermostat inside the elbow coming off the front of the engine (where a 4.0 wd have it) - so in effect I had two t/stats - and the top one was majorly blocked and caused an over-heat first weekend - needed removing. If you think that might be the case remove the top hose and poke a screwdriver in and see if there's something in there.
Do you get interior heat?
As Theo R noted, you can't leave the system unpressurised for too long without a cap: if you run it to temp with no cap you can easily get boil over, as the air expands unpressurised; if you run the engine with the cap on unbled air will still expand and spill over into the overflow; and lastly, if you put the cap on when its merely warm (and not yet boiled over), as it cools it will collapse the top hose under the vacuum - so, you need to get in and bleed the air quickly after start-up.

If you've tried one bleed procedure without success then you cd try this (no reason it shd be any better really tho): park nose up somewhere (and if you have nanocom deflate the rear EAS and leave a door open), fill the reservoir up, start, level will go down, milk the top hose, top up coolant, use the throttle cable to hit 2000+rpm (res cap off), keep it there until you see the coolant "wee" out of the hole on the inside of the top of the reservoir - it shd be a pretty strong jet, and no air bubbles. You say you had no stream but that means you don't have enough coolant (needs topping off when the system cools)/ there's a blockage (but you've done the rad)/ the water pump is toast/ the t/stat is "wired" incorrectly. If the coolant starts steaming off then let the system cool (cap off), top up, and start again. It may take two/ three cycles to drive all the air out.

BTW When you tap off the coolant from the radiator, if it looks good/ you know it is fresh you can use it again, and then if the system is not taking at least the same volume back then you know you have trapped air.
 
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If all the air is out but nothing coming back through the bleed hole, there's no flow which would point to the water pump (or a pretty major blockage as Rob says). The 4.0 SE I used to have would do the same thing. Initially it would overheat after about 30 miles, which got shorter and shorter until I could start it up, leave it idling and it would overheat after about 10 minutes. New water pump cured that totally.
 

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Thanks. I did that process. Twice actually. 2nd time drained/refilled (just through radiator drain plug). Both times, the radiator to header tank hose flowed strong for about 15-30 seconds. Then it would flow to a drip, very small stream (flowing down edge of tank) or even nothing at all. Then boil...

Upon 2nd fill, the reservoir was very slow to drain. Even when I first started putting coolant back in.
Romanrob, thanks for the detailed write up! I'll take a look at all of this.
hi this is how i fix mine,its worth a try? fill tank so its full up,fill a 2 litre coke bottle 3/4 full with water,invert bottle into header tank,it will stay there on its own,you will now see air bubbles coming up in coke bottle,wait till air bubbles stop leave bottle in tank,start engine ,from cold,wait till you get flow from tube on radiator,then no more air bubbles,apart from small hose flow,take off bottle ,take out excess water from tank,to proper level,put cap on,do all this before engine gets hot,or to warm,it works for mine,4.6 1996 gems,good luck,
 

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Discussion Starter #14
First... And again... can't thank you all enough for your help.

Romanrob (or anyone else), you asked about heat. Interestingly, when I stopped the truck at its current resting point (about 5 months ago maybe) the heat was not working. And even as I tried to bleed air out over the last few days, I'm not certain, but I don't believe the heat was working then either. For whatever reason, this time, the heat was working and the bleeder line to the reservoir was flowing strong. I'm currently on my second bleed cycle with your process. I'm not letting the truck get too hot (almost to mid way on temp gauge but not mid way- although I know those aren't the best).

So I guess my question is: is no heat an indication of air in coolant system? And if heat came back, is that an indication that I got air out?
 

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Pretty much...having heat thro hvac is good...no heat cd be air, or a lack of coolant flow. Have you checked the upper tstat hoses according to Rave btw?
Sounds like you are on the right track tho
 

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Discussion Starter #16
Rob, I did look at the tstat hoses yesterday- they seem to be appropriate.

This evening, I decided to take off tstat and boil in a pot. Found 2 things:
  1. I'm really really hoping I found the issue here. When taking the tstat off, the port from the reservoir was blocked with what appeared to be an old reservoir cap gasket. I removed and refitted- I'm currently in the process of bleeding. But was able to get the truck up to a higher temp than I had before without boiling... Fingers crossed...
  2. After boiling the tstat, I would run cold water down the header tank port. It did close fairly quickly. However, it did not seal 100%. If you filled up the top ports (after it had closed), the water would drain through the lower hose port in maybe 20-30 seconds (pretty slowly). Is this normal?
Now onto the other laundry list of issues? lets hope! I'll update you once I cycle this one through.

Many thanks.
 

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+1, all sounds good but a blockage would account for the lack of flow that it appears you had before.
 

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Discussion Starter #19
Well, I guess I was wrong on getting rid of my issues.

I'm wondering if I have a water pump issue. The coolant continues to boil over. I believe that when I thought I had gotten the air out, I was just keeping the throttle open too much when bleeding (if kept around 2,000 rpm, the header tank won't boil over).

Take a look at the 2 photos:
photo 1 is at startup or when revving the engine
photo 2 is when I let off the throttle or after the initial startup (will flow strong for a few seconds at startup)

Is this normal?
 

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Seems like you are getting there but you should get a continuous stream all the time, not only when you rev it. That suggests the impeller on the water pump has corroded so it isn't pushing the coolant around as it should.
 
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