Not sure if I'm getting proper coolant flow through radiator.

[Mad4Mud]

After installing a reco ZD30 in my GU3 I filled the cooling system and ran motor to get any air out of system. Turned heater on, even removed fan, and even though the temp gauge showed it was at operating temp the bottom return pipe to the radiator from thermostat housing still felt cool to touch. Top radiator hose was too hot to hold for long. I got mechanic to swap thermostat for genuine one. Same result. Has never over-heated. Had it checked by radiator shop and they couldn't find a fault. I still can't get my head around the what logic tells me: If the return pipe's cold, there's no flow through that pip. Can anyone shed some light and maybe put my mind at ease?

[AB]

With the engine cold and the radiator cap off can you actually see water returning to the top of the radiator?

[Mad4Mud]

Hi, AB.
I can see coolant moving in the reservoir tank with its cap off but not in the radiator with that cap off.

[Sir Roofy]

if you have a genuine themostat the tempreture that it opens at should be ok if your temp gauge is reading normal every thing should be ok
take it for a run and see what the temp range is should go to at least halfway

[Mad4Mud]

Thanks, roofy.
Did take it for decent run down Hwy. Temp gauge showed a frag under half way. Bottom engine pipe back to radiator still feels cold to the touch though. Can't get my head around it. Might be a case of me being a little paranoid and seeing ZD30 melt down lurking in every shadow. Thanks heaps for your input.

[Sir Roofy]

Thanks, roofy.
Did take it for decent run down Hwy. Temp gauge showed a frag under half way. Bottom engine pipe back to radiator still feels cold to the touch though. Can't get my head around it. Might be a case of me being a little paranoid and seeing ZD30 melt down lurking in every shadow. Thanks heaps for your input.

thats ok mate waas going to say that but seeing as you did yep could be
have a look in your owners manual and see what temp range your themostat opens at that will put your mind at ease

[patch697]

Although I wouldn't expect it to be dead cold as such, if your radiator is working efficiently then you should have a fairly significant temperature drop at the bottom outlet.(much cooler bottom hose)
This is the outlet that returns the tempered coolant back to the engine.

By all means it is better to be safe then sorry especially when you've just replaced the engine but if the engine is showing no signs of overheating & you've had it all checked out & theirs no problems found then I'd say your system is working very efficiently.

[macca86]

try running it with no thermostat and see how that goes? Had similar problem in my commodore and also had normal temp readings when really car was over heating due to leaking water pump

[Mad4Mud]

Cheers, Patch. I had it in my head that the flow was the other way. I think the position of the thermostat had me confused. Bit easier to get my head around now that I've been enlightened a bit. I'm pretty sure the thermostat is 82 deg C. Still have to install exhaust temp gauge as the last anti-bang measure, fingers crossed, I'll get around to enjoying it instead of cursing it.

[Mad4Mud]

I reckon I might take your advice, macca. Got an old thermo I can cut guts out of and still use rubber gasket so she'll seal. If nothing else I'm curious as the spot where temp gauge now sits is a frag higher than when I first got the Patrol (had 82k on clock) and about the same as it did when it all started to go wrong (roughly 130k on clock). Will post any noticeable differences.

macca, could i ask where the quote came from? Thanks again.

[Gentle Ben]

This is a much later post, nearly 10 years later, but did any light come of this?

I'm having the same problem, top pipe is hot, bottom pipe is cold. Thermostat is OK, and a good drive gets the engine up to operating temps, but the bottom part (like bottom 3/4) of the radiator is still cold, and the bottom pipe is cold.
Coolant doesn't seem to be flowing through it. Car isn't overheating. Wondering about airlocks etc.

Bewildered, and going to pull out the water pump to inspect.

[nipagu7]

that sounds about normal . top hose has hot coolant from motor to radiator , bottom hose has cooled coolant from radiator going to the motor , just keep an eye on the over flow bottle and make sure it is filled up to to the minimum mark when the car is cold . the pressurised bottle beside it should be full .

[threedogs]

If in doubt park uphill some where steep ,cut the bottom off a 2lrt Coke bottle
tape that to the top of the radiator outlet and fill with coolant, well a bit of coolant
youll see any or all air disappear.
My mechanic told me they were self bleeding