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cbjroms 13th September 2020 20:05

Cooling System Problem
So I am running a Herald 13/60 engine in my (Sammio) kit car. The top of the radiator sits lower than the thermostat housing due to the shape of the bonnet. So, in the hose which connects the bottom of the radiator to the thermostat housing I have added a T piece, one limb of which is connected to an expansion tank. The expansion tank sits slightly higher than the top of the thermostat housing.

I was out in the car this afternoon and noticed that the temp guage was reading very high. First thought was that the temp controlled radiator fan had failed but that all checked out fine. Then I noticed that the radiator felt cooler than anything else and that the expansion tank was bubbling. I carefully removed the pressure cap from the expansion tank (it was full to the top) and lifted it higher above the engine. There was a gurgling noise, the level in the tank dropped back to normal, the radiator heated up and the fan kicked in.

I had presumed that with the exapnsion tank being higher than both the thermostat housing and radiator, any trapped air would make its way to the expansion tank. But today, the air seems to have collected in the radiator. What am I missing?

cbjroms 14th September 2020 19:49

I have put some photos onto piston heads:

Mister Towed 14th September 2020 21:02


Originally Posted by cbjroms (Post 105160) the hose which connects the bottom of the radiator to the thermostat housing I have added a T piece, one limb of which is connected to an expansion tank.

What am I missing?

There's your problem, the thermostat housing should be connected to the top connector on the radiator, and the pipe to the expansion tank should connect in as high as possible in the top hose.

Otherwise, any air trapped in the cooling system would have to travel all the way to the bottom of the circuit before it could enter the pipe and escape into the expansion tank and air doesn't like travelling downwards in a liquid.

One way of avoiding trapped air in the first place is to disconnect the top hose from the thermostat housing and fill the system through that hose until coolant comes out of the housing. Also don't forget to pre-fill the heater matrix if you have one fitted.

Finally, the symptoms you describe could be due to head-gasket failure allowing compression gases to overpressurise the system. Check for 'mayonaise' stuck to the inside of the oil filler, it's not always present but it's a giveaway if it is.

Hope that sorts it.

cbjroms 15th September 2020 15:16

Thanks Mister Towed,

My description was incorrect. The top radiator hose does go to the thermostat housing. Bottom radiator hose feeds from the water pump.

On Pistonheads the suggestion is that I need to change:
a) Expansion tank should feed into bottom radiator hose.
b) Add connection from radiator filler drain (always open on Honda radiator I think?) to the expansion tank top (but not vent).

Does this make sense?

Grey V8 Pete 16th September 2020 11:26

Hi! I would offer the following which I hope will solve your problems.
Yes a coolant hose should ideally go uphill from the thermostat so natural convection aids the flow. However you should be ok provided the water pump is in good condition and the radiator and engine are free from sediment build up.

On your pistonheads photo there should be a plain sealing cap on the radiator at 4 so it seals on the top face of the rad boss with no spring or pressure relief. There should only be a pressure cap on top of the expansion bottle 7.

The hose 6 needs to be Teed off immediately after the thermostat housing which is where any air will tend to collect.

Hose 6 needs to be small bore (mine is 8mm) so that as the coolant heats up and expands it will expel any air up into the expansion bottle.

The small bore hose attached to the top neck of your expansion bottle 7 is an “overflow” drain and so should be open ended and finish down under the chassis.

The expansion bottle should not be filled up! Leave about 1” of coolant above the lower connection which should be ample. Keep a check on this after the first few start and cool down cycles and top up as required to replace if any air has been expelled from the system.

Finally I would fill your coolant system from empty as follows:
Remove the plain seal cap from the radiator.
Remove thermostat housing and thermostat.
(I would fit a new thermostat anyway at this time as a precaution.)
Start filling system through the thermostat housing keeping an eye on the open radiator filler hole!
When the coolant level reaches the radiator neck replace the seal cap.
Important! Check now in the workshop manual to see if there are any bleed vents on the engine that need opening to remove air locks.
Continue filling until the coolant level reaches nearly to the top of the thermostat housing.
Fit the (new!) thermostat, new gasket and thermostat housing cover.
Continue adding coolant through the neck of the expansion bottle until it is about 1” above the bottom inlet.
I would then unbolt the expansion bottle from the bulkhead and raise it up for a while so any air bubbles can escape.
Rebolt the expansion bottle in place.
Recheck there is still 1” coolant above the lower connection.
Replace the pressure cap on the top of the expansion bottle.
Start the engine and allow it to warm up, keeping an eye on the temp gauge and check the top hose gets hot when the thermostat opens.

Finally recheck the coolant level in the expansion bottle when the engine is cold.

Hope this rather lengthy post helps. Let us know how you get on. Peter.
P.S I have this layout on my V8 engine and it works well!

cbjroms 17th October 2020 18:42

@Grey V8 Pete a belated thank you for the above advice and guidance.

I have changed the system so that the 25mm spout on the bottom of the expansion bottle is now connected by rubber hose to a T piece in the bottom radiator hose (as per pistonheads advice).

Rather than fit an air bleed into the top radiator hose or thermostat housing, I remembered that my initial plan had been to unbolt the radiator and lift it above the thermostat housing when filling the cooling system. This should allow any air trapped in thermostat housing to escape?

cbjroms 18th October 2020 21:23

Yesterday I unbolted/lifted the radiator so that its filler was above the thermostat housing. I fllled the radiator until the water was level with its neck - thus I knew that the thermostat housing and radiator were filled with water and that there was no air in that hose. The expansion bottle cap was in place and the level was correct as per the marking on the bottle.

Leaving the radiator cap off (as it was temporarily higher than the thermostat housing) I ran the engine until it got warm and then replaced the radiator cap and continued to run the engine until everything got nice and hot (temp gauge read normal). I then turned the engine off an allowed to cool, at which point I removed the radiator cap and found the radiator was not full to the top. So I loosened the expansion tank cap, water started to come out of the radiator filler and so I repaced the radiator cap. Went through this cycle a number of times (radiator was clearly getting very hot) before lowering the radiator down and bolting it back into position.

On road testing the car the temperature gauge remained unusually low but when I got back and stopped in the garage the expansion tank starting venting water, all hoses felt hard (there seemed to be bubbling/boiling in some of the hoses) but the radiator was cold to the touch. I also noticed that a couple of new water leaks had developed and thinking that the cooling system was over pressurising? After the engine had cooled, I removed the radiator cap and it looks as if there is no water in the radiator.

Could a stuck thermostat cause water to be pushed out of the radiator into the expansion bottle?

Lucky@LeMans 18th October 2020 22:08

Could be a failed head gasket . If the hoses were hard they were under pressure. But if the radiator was cold it must have been full of air rather than hot water. If all the water was pushed into the expansion tank and escaping through the vent I can't think it would be anything else. Is the coolant that is coming out brown and sludgy ? If it is then most likely head gasket.

Grey V8 Pete 19th October 2020 10:26

Have a look at the first few paragraphs of my earlier post. If you Tee off the top hose for a small bore pipe to the expansion tank then it will automatically purge air in the system as that will always float to the top. Air has a habit of coming out of the coolant during heat up so this system will automatically get rid of it and replace it with coolant during cool down.
Did you fit a new thermostat? If that has failed “shut” you could get your current symptoms. As Lucky@LeMans says it could be a head gasket due to the amount of pressure you are getting.
Did you bleed all the air out of the heater circuit? Make sure the heater valve is open (set it at fully hot position if the valve is part of the heater control). I have bleed valves in both heater lines. Available at CBS in diameters to suit popular hoses. Link below.
Gauge will read quite low if there is no coolant in contact with it, which indicates that your cylinder head is empty! Peter.

cbjroms 19th October 2020 12:28

Thanks for the help guys, really appreciate it.

@Lucky@LeMans - running the engine (up to nomral on the temp gauge) with the radiator or expansin cap off, I do not get any bubbles which would be expected it is head gasket? The coolant is a little brown but not partcularly sludgy. Hoses were defintely hard after road test and the radiator was cold so it must have been full of air rather than hot water.

@Grey V8 Pete - the heater circuit is bypassed (heater in connected to heater out). Your 'Gauge will read quite low if there is no coolant in contact with it, which indicates that your cylinder head is empty!' is interesting. Running the engine on the drive for 20 minutes gets the gauge into the high position at which point the electric fan cuts - so under these conditions head is full of water. But on road testing the gauge barely rises and this is when the problems are occuring. Perhpas I will try road testing without the thermostat in place.

Lucky@LeMans 19th October 2020 16:35

Running the engine at tick over on the drive the engine might well behave as normal. If the head gasket is only just at the cusp of failure it might only show itself as faulty when you drive the car under load. When driving the head gasket takes more load as does the cooling system in general.

Grey V8 Pete 19th October 2020 20:00

Pull the dipstick and see what it looks like. Clear or dirty oily is normal. Something that looks like mayonnaise shows water (e.g. from a failed head gasket) :fear: is getting into the sump and emulsifying.

Plumb the expansion tank into the top hose and you will see immediately if air (or steam! ) is entering the system! Simples! :high5::high5::biggrin::biggrin:Do it now! You know it makes sense!

Mister Towed 20th October 2020 07:27

I'm with Lucky, the symptoms suggest a failed head gasket. I had the same problem on my Midget - it ran fine for nearly 200 miles back from Goodwood in 2018 with the temperature gauge staying below half way, but started making odd noises, a bit like a slow running steam engine, with about fifteen miles to go.

I arrived home and turned the engine off and everything seemed fine, but a minute or so later about three litres of coolant gushed out of the expansion tank in big pulses.

Each time I took it out after that it did the same thing, it ran fine and the gauge said it was cool, but it would vomit coolant all over the road a minute after shutting down.

The coolant wasn't unusually sludgy and there was no 'mayonnaise' in the oil, but after checking everything else I decided that it must be engine gases over-pressurising the cooling system.

I whipped the head off and sure enough, there was a fine crack across the gasket on one cylinder. After a clean up of the mating surfaces and a new Payen gasket, I haven't had a problem since.

Good luck getting it sorted :)

cbjroms 20th October 2020 13:06

Thanks again everyone,

I intend to plumb the expansion tank into thermostat housing anyway, but suspect that the root cause of the problem to be the head gasket. I cant really see trapped air being the cause of such extreme coolant vomitting. Whatsmore my symptoms are exactly as Mister Towed describes.

cbjroms 20th October 2020 17:23

Decided to whip the head off this afternoon. Gasket, head surface and block surface look absolutely fine. Put a bit of fuel in the cylinders and no sign of any leaking out. Did the same with the head and 2 and 3 leaked whereas 1 and 5 held the level. This makes sense as I know that the compression in 2 and 3 was 20psi lower than 1 and 5.

Lucky@LeMans 20th October 2020 17:32

Ok, so you'll be eliminating the head gasket once a new one is fitted and torqued down. It can be a pain in the ar** getting to the bottom of these sort of faults !

Put a straight edge across the head just to make sure it is flat before you reassemble it.

Grey V8 Pete 21st October 2020 09:25

Not to do with the original topic but you mention checking the head for leakage. I presume you mean around the valve seats? There shouldn’t be any leakage so its worth taking the valves out and checking / regrinding the seats while it’s all stripped down. Has the head been converted for unleaded fuel? If not you may want to consider this as it saves the hassle of adding valvemaster stuff to the fuel every time you fill up. I did this to my 1955 classic years ago and it’s run well on unleaded ever since.

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