3.5 RR classic cooling issue

[rob588]

Hi,

I recently purchased a CCV 80 inch trialer with a 3.5 V8 (mid 80's) RR engine, running on twin SU's. The temperature gauge was faulty when I purchased it so I installed a mechanical gauge. Immediatly after installing the gauge I started getting strange readings, it would tick over for 5 mins and the gauge would show zero, suddenly it would go to 80 degrees and it would then flucuate all over the place however, with the fans on I could maintain 90 degress ish (stationary). Due to it not being road legal I hadn't been able to drive it anywhere, until a recent trial. At the trial the gauge was rockting up to 100+degress regularly, and water was leaking out of the expansion tank. I wasn't happy running it so warm so I packed in the trial.

Having since looked at the plumbing in more detail, I had two small hoses at the top of the radiator, one going to the expansion tank and one going to the top of the inlet manifold. The hose at the bottom of the expansion tank fed into the TOP hose on the radiator, this hose was almost horizontal to the ground. When I was going up hill water was running from the TOP hose back to the tank, causing it to overfill !! I completed a sniff test and that proved to be clear. I also checked the thermostat and it didn't have one......which I believe is fine in a trialer.

I have since re-plumbed the system so that the expansion tank drops down vertically and T's into the LOWER radiator hose. The other two small hoses are connected as they were, one to the expansion tank and the other to the inlet manifold. I then filled the system (nose in the air) and ran the engine. The temp gauge shot up to 100 degress, but on a positive, the expansion tank settled nicely, and wasn't being fed from the radiator hose as it was before, so no over flowing from the tank. I managed to clear the air from the system and the temp sat comfortably at 72 degress with the fans on (stationary) for a good 30 mins..........so, I think I've now sorted the over heating issue, but I guess I won't know that for sure until I attend the next trial.

However, I've now developed a new problem.......everything seems to be functioning 99% correctly apart from the fact that the aluminium expansion tank is getting really hot to touch. When the engine is at 72 degress you can only touch it for about 5 seconds. If you turn the fans off and allow the temp to get to 90 degress you can only touch it for about 2 seconds. To clarify, the tank remains really hot even if I remove the small hose that goes from the radiator to the expansion tank. The heat can only be coming from the lower hose connection and/or from the heat of the engine (theres not much space under the bonnet). But, it doesn't make much sense because the engine is only running in the 70's and the lower hose from the radiator is very comfortable to touch.......where is the heat coming from ??

A couple of points worth mentioning.....I used a laser thermometer and took various readings.

Everything in the engine bay (thats metal) feels very hot. The alternator which is very near to the expansion tank was about 65 degrees.
I haven't managed to test it whilst actually driving. Is it being caused by the heat sitting in the bay due to no air circulation ?
When the top hose is around 75 degress the bottom hose is around 60 degress (this suggets the radiator is woking effectively ?), is it just convection from the water in the lower hose heating the water in the tank and the tank itself ?
There are NO bubbles in the expansion tank now that its bled properly and the level of the water in the tank is remaining very constant, this feels positive ?
The truck is running with two new, decent, electric fans.
I may well be getting some of the terminology wrong (header tank/expansion tank).....this is all new to me.

Sorry for the long message, but I wanted to give everyone the full picture !

In summary, why is my expansion tank getting so hot.......is it just because the truck was stationary when I tested it and therefore getting no air ciculation ? I guess, if the lower hose is around the 60 degree mark, due to convection, the water in the tank and the tank itself would run at a similar temp........it just felt too hot !!! If it not this.....where have I gone wrong !!??



Thanks

[Ian Anderson]

The way I read it the expansion /header tank now forms part of the flow of your system…..from radiator top and manifold top to tank to bottom hose so the heat of the fluid out the engine will be the heat of the header tank. I would also put in some restrictor to allow minimal flow to clear any air but reduce fluid flow as much as possible…restrict or sin hose from top of manifold and top of radiator hose to bottom hose stays unrestricted.

Reason for the restrictions is to force as much fluid as possible through the radiator and not allow a secondary major flow route.

Where is your pressure cap located? I presume on the header tank and that the final fill of the system is done from here.

Once full of fluid crack the temperature gauge fitting to relieve any air that may have collected there…..that could account for variations in the reading.

Sounds like a fun car

Ian

[rob588]

Thanks for the reply Ian, much appreciated.

Yes, the pressure cap is on the tank.

To clarify my understanding, the two small hoses that go from the radiator and manifold to the tank should be restricted ? But the hose that goes from the tank to the bottom radiator hose shouldn't be ? Whats the best way to restrict the flow ?

Are you saying that the heat in the tank is not concerning ? Is it made worse by that fact that the tank is made of aluminium ?

Thanks again.

[Ian Anderson]

As a restrictor I used a bit of barthe diameter of the hose with a 2 mm hole drilled through. Many ne was a 1/2 inch hose so actually used a plumbing copper pipe with a stop end soldiered in place then drilled the 3 mm hole

If the top hose is at say 90 degrees any flow from top of radiator is thus 90 degrees and the tank will get there after time depending on flow rate. So aluminium tank would be my preference over a plastic one…… but causes another problem in that you cannot see fluid level till car has cooled and pressure cap removed

I suggest a dip stick kept in the car and marked at a level once the engine has cycled to temp. Or you end up filling and blowing excess out every time you run the car

Ian

[rob588]

Thanks again Ian, thats really helpful.

The heat generated from the tank is not ideally how I would like it to work. I really do have no knowledge with cooling systems so bare with me on this one ! Having read many posts on line I think there may be another solution but I wouldn't mind running it by you, if thats ok ?

If I did away with the connection from the bottom radiator hose to the tank. And then replaced the aluminium tank with one of the tanks below. And then ran the small hose from the top of the radiator to the connection on the new tank, would this work as an effective cooling system ?

If so, the benefit would be that there would be less heat in the tank ? I assume the connection on the tanks below go to the bottom of the tank so that when the engine cools the system would pull the water back into the radiator allowing it to expand and contract ?

Would the plastic tank below still accept/need the same pressurised metal cap ?

With this system I assume I'd have to fill the cooling system from the radiator itself, not from the tank ?

Any thoughts or views ?

Apologies if I've got this totally wrong !!

Thanks again.

[Ian Anderson]

Not sure your pressure cap would fit on the first plastic tank, the second looks like a standard cap fitting

For your suggested idea the top radiator overflow would have to go to the bottom of the header tank so that it runs uphill from radiator so any bubbles generated will float upwards to reach the tank….. but what about the pipe from the top of manifold…..what will you do with that?

The system I described earlier was as I used on my GT40 where additional height above engine is not possible
The header tank ran at the temperature of the engine and I never thought much about it………because the 40 runs a rear engine and front radiator it had a bleed nipple on the radiator one thing I did at the start of season was crack the bleed nipple and in15 years never had more then perhaps an egg cup full of air in the radiator and the manifold bleed went through the header tank so no bubbles there.

Must say in a Landy runnng slow I would add some bonnet vents to let hot air escape…..the more heat that escapes the better!

Ian

[rob588]

Thanks Ian, once again, the information is really helpful.

Can I pick your brains with your sentance below ?

For your suggested idea the top radiator overflow would have to go to the bottom of the header tank so that it runs uphill from radiator so any bubbles generated will float upwards to reach the tank….. but what about the pipe from the top of manifold…..what will you do with that?

If I connected the top radiator overflow to the bottom of the tank, it wouldnt be going up hill. But it would be going uphill if I connected the top overflow from the radiator to the top of the header tank.

I've done a very basic drawing below......the orange line shows how it would run if I connected it to the bottom connector on the tank. The purple line shows how it would flow on the top tank connector ?

The manifold pipe would stay connected to the second overflow outlet on the rad.

Thanks

[FBW]

Hello,

I think your design won't work correctly.

As we all know, water expands when it gets hot. But when it gets cold, it contracts again. We also know that water begins to boil at 100°C. It's important to note that this only happens at typical atmospheric pressure.
In the context of cooling systems, it's also important to know that air bubbles rise to the top...if nothing else prevents them from doing so.

You write:

Having since looked at the plumbing in more detail, I had two small hoses at the top of the radiator, one going to the expansion tank and one going to the top of the inlet manifold. The hose at the bottom of the expansion tank fed into the TOP hose on the radiator, this hose was almost horizontal to the ground. When I was going up hill water was running from the TOP hose back to the tank, causing it to overfill !! I completed a sniff test and that proved to be clear.

I also checked the thermostat and it didn't have one......which I believe is fine in a trialer.

The hose on the carburetor dome is at the highest point on the engine. Air would collect there. The hose directs any air bubbles toward the radiator. It doesn't matter whether it runs horizontally, downhill, or uphill.

This is because the water pump pushes the water through the engine and from there through the radiator. The inlet from the radiator to the water pump is probably located at the bottom of the plenum chamber, below the small hose connections. The water pump therefore draws water not far from the small connection.
Therefore, there is significantly less pressure at the small connection than in the carburetor dome. This results in water, and if present, air, being constantly drawn from the carburetor dome to the radiator.

This ensures that the air initially collects in the radiator.

It also ensures that the intake manifold warms up quickly. This ensures a shorter warm-up phase.

So. Now the air is in the radiator.

As the coolant heats up, it expands. The pressure in the system increases. There is no outlet for the volume other than the second small hose to the expansion tank.

So the volume pushes there.

Since there may be air in the radiator, and this is located directly in front of the hose connection, the air from the radiator is first forced into the expansion tank.

It is better if the expansion tank is positioned as high as possible, but the pressure differences that also exist here also push the air downhill into the tank.

The hose is inserted into the lower connection of the expansion tank.

Functionally, the plastic and metal tanks are the same. In both cases, the lower connection opens at the very bottom, although it looks different on the metal tank. If you look inside, you can see that the connecting pipe extends almost to the bottom.

So now the air is in the expansion tank.
This must(!) have a special pressure equalization cap. I've been using the original cap with the 15-PSI imprint on my V8 for years.

Two valves are integrated into the cap.

"A pressure relief valve": If the engine expands because the water, and therefore the engine, gets hot, the pressure relief valve maintains the pressure up to a certain level. This increases the boiling point, and the water only boils at 105-110°C. This is very important for the engine. Even if the gauge shows 90°C, there can be hot spots in the engine that are significantly higher. If the water starts to boil there, the cooling effect is reduced.
If the pressure rises above the intended limit due to expansion, the cap releases the pressure. First, the air that was once in the engine flows out.

The excess pressure ends up in the small space between the cover and the valve. This is also where the second pipe connection opens. A hose leads down to the outside.

Another valve, a vacuum valve, must be integrated into the cover: When the engine cools down, the volume of the coolant changes again. This causes the vacuum valve to open and let air into the expansion tank. But! The connection to the radiator is at the bottom of the expansion tank. This means that only water flows to the radiator. It's important that there's enough water in the expansion tank. Too much isn't a problem. It's pushed out during the first warm-up, and the level is correct when the engine cools down.

A few more words about the thermostat valve:
It makes sense to have the valve installed. It reduces the warm-up time and keeps the engine at the right temperature. A valve at 74°C is very cool. That's not particularly good if everything is OK. I would install one with 82°C. You can also remove the small check valve (plastic ball with a metal fork). This will ensure constant flow through the thermostat and react more quickly. However, the engine will only warm up slightly slower.

All in all, I think the system was properly connected before. I would reinstall it.

Check carefully to see if the expansion tank cap is properly positioned. Change the thermostat valve to 82°C.

Oh, and the temperature gauge sensors aren't very good either, and they're showing strange readings. Checking with an infrared thermometer helps enormously.

Best regards,
Frank

[rob588]

Thanks Frank, thats really informative.

So, in summary, you would suggest sticking to the way I have it plumbed now (bottom radiator hose plumbed into the base of the tank, with the inlet manifold small hose to the radiator and the other small hose to the tank). Since I plumbed it this way its been operating perfectly, other than the fact that the header tank gets hot.

The original owner had the top radiator main hose plumbed to the tank, the hose was almost horizontal to the ground. This was causing the over heating issues. As soon as you pointed the truck up hill the top radiator hose would fill the tank and it would over flow. After a few hours trialing, the water level had dropped significantly. As I have it now im not getting any of these issues.......thankfully. Temp is fine, no air bubbles, the water level rises and fall as it should when the engine heats ans cools.

I only thought about plumbing it like I showed in the pic to prevent the tank getting so hot......but I think you're right. If it ain't broke, don't fix it ! I also have the benefit of being able to top the system up from the tank this way, which is easier.

Thanks again.

[FBW]

The correct answer is:
# 1x Small hose from the carburetor dome to the radiator.
# 1x Small hose from the radiator to the lower expansion tank connection.
# 1x Overflow from the upper expansion tank connection to the outside.





What do you mean by:

...bottom radiator hose plumbed into the base of the tank...

Regards
Frank

[rob588]

Hi Frank,

Thanks for the reply......my system is currently set up slightly differently.

The main bottom hose (outlet) from the the radiator (the one that goes to the water pump). Has a 'T' in it, this 'T' goes to the bottom of the tank. As it is, everything is working perfectly, apart from the fact that the tank gets hotter than I'd like, I think it's not helped by the fact that the tank is aluminium.

I'd contemplated plumbing it like yours which would allow me to use a brass tank and hopefully resolve the tank heating up.

Thanks

[FBW]

The main bottom hose (outlet) from the the radiator (the one that goes to the water pump). Has a 'T' in it, this 'T' goes to the bottom of the tank. As it is, everything is working perfectly, apart from the fact that the tank gets hotter than I'd like, I think it's not helped by the fact that the tank is aluminium.

I'd contemplated plumbing it like yours which would allow me to use a brass tank and hopefully resolve the tank heating up. :

If you connect the lower hose leading to the water pump to the expansion tank via a T-piece, you've solved the expansion function. But! Air might collect at the top of the radiator. This isn't automatically vented to the outside. That's not good.

A hot tank isn't a problem as long as the temperature stays well below 500°C. Above that, there's a risk of the aluminum melting.


If there was a lot of air in the system during the first test drive, it's quite possible that the temperature fluctuated abruptly. As long as there's no water at the sensor, the sensor doesn't detect the water being hot.

If there was water in the expansion tank, the system vented itself, and the water "migrated" from the expansion tank to the radiator.

You mistakenly attributed this to the gradient. In reality, the water replaced the air.

With few exceptions, the designers put a lot of thought into how something should work. It takes good ideas to improve it.

Regards
Frank