Is my water pump belt slipping?

[richardpope50]

I have a cooling problem ….

- Checked /re-calibrated ECU temp gauge and compared to multi-meter – it’s pretty accurate.
- Start engine from cold and just idle at 900 rpm
- Cabin heater pipes warm first as expected
- Radiator keeps cold until thermostat opens
- Thermostat opens around 80
- Engine temp rises to 94 and otter switch for first stage (Kenlowe) fan comes on.
- Temp holds at 93/94 but does not decrease
- Closing cabin heater valve made no difference
- Rad core where fan is, is cold to touch. Outside fan area too hot to touch.
- Rad input hose read 88, output read 72 so some 16 degrees drop.
- Raised revs to around 1,700 rpm for a few minutes and temp slowly climbed.
- Second stage fan came in at 95 and temp still slowly climbed reaching 98 when I switched engine off.

Went for a run and generally much the same with temp climbing to 100 when we stopped to cool down.

So, the problem seems to be not enough water flow especially when revs increase. I’m unlikely to have air lock except possibly just in short section of top hose. So what’s wrong?

Options?
1.) I have wondered for a long time if there is enough belt length driving the pump. It’s only three or four inches of contact. However belt does not appear to slip – no leak, no squeal, no bearing noise, all firm and no polishing of pulley nor belt face.

2.) Are pump impellers so rusty / corroded they cannot shift water? Engine only 44,000m and stored empty of water for recent years. Before that was on road for six years so probably had antifreeze to protect it.

3.) Blocked waterways? Not much rust coloured water comes out.

Questions:
1.) Is a 16 degree temperature drop across radiator about right?
2.) How can I check if the pump pulley is slipping?

Any other comments appreciated.

Radiator is a 65mm deep core, fan is a high capacity two stage Kenlowe 12" fan rated at 1,250CFM and 1,850CFM at second stage.

[stevieturbo]

Are you turning the pump the right direction ?

Was yours and the pump always a serpentine drive ?

ie, you're driving off the back of the belt, whereas old V-belt would be the front side.

[richardpope50]

It's a 1997 serp engine so yes, driving correctly as per original belt.

[DEVONMAN]

Has the top of the rad got a bleed screw.
Reason I ask is because the top hose has a drop loop to the swirl pot so there is no route for any air to naturally purge from the top of the rad.

[DEVONMAN]

Sorry, Just read a previous post so you have got a bleed point at the top of the rad.

[ramon alban]

Hello Richard,

You make no mention of coolant system pressure.

I think your symptoms point towards a faulty pressure cap or its associated sealing rim.

Coolant is being allowed to boil at 100 deg C and generate superheated steam around the exhaust manifold region which migrates upwards through the galleries to the inlet manifold and gauge sensor area, showing up as overheating on the cabin gauge.

If pressure is correct at around 15 psi, then the coolant cant boil and generate steam until approx 120 to 130 deg C,

This allows the control components (thermostat, pump, radiator and fans) to do their proper job safely below 100 deg C.

Furthermore, if a pressure cap is faulty any inevitable steam pressure at 100 deg C also expels fluid thro' an overflow pipe and when it cools slightly air is allowed to enter the system, creating even more problems until it can be expelled manually.

All the above is typical of an RV8 fitted to an SD1 with a faulty pressure cap.

It may not apply exactly to a different system, but - hey - you've tried everything else.

All the above is explained (including some scientific analysis) in detail in my PDF essay on SD1 RV8 cooling.

Follow the PDF link from here: http://www.vintagemodelairplane.com/pag ... ing01.html

From that essay, discover some other possible causes, such as an unknown coolant leak, crud in the system affecting coolant flow, water pump impeller blades eroded, fans not shrouded, etc etc.

Have an enjoyable read!

[ramon alban]

Hello Richard,

You make no mention of coolant system pressure.

I think your symptoms point towards a faulty pressure cap or its associated sealing rim.

Coolant is being allowed to boil at 100 deg C and generate superheated steam around the exhaust manifold region which migrates upwards through the galleries to the inlet manifold and gauge sensor area, is showing up as overheating on the cabin gauge.

If pressure is correct at around 15 psi, then the coolant cant boil and generate steam until approx 120 to 130 deg C,

This allows the control components, thermostat, pump, radiator and fans, to do their proper job well below 100 deg Cl.

Furthermore, if a pressure cap is faulty the steam pressure at 100 deg C also expels fluid thro' an overflow pipe and when it cools slightly air is allowed to enter the system, creating even more problems until it can be expelled manually.

All the above is typical of an RV8 fitted to an SD1 with a faulty pressure cap.

It may not apply exactly to a different system, but - hey - you've tried everything else.

All the above is explained (including some scientific analysis) in detail in my PDF essay on SD1 RV8 cooling.

Follow the PDF link from here: http://www.vintagemodelairplane.com/pag ... ing01.html

From that essay, discover some other possible causes, such as an unknown coolant leak, crud in the system affecting coolant flow, water pump impeller blades eroded, fans not shrouded, etc etc.

Have an enjoyable read!

[richardpope50]

Ramon,

Many thanks for your suggestion and I have read your PDF - interesting.

I have no idea what the pressure of the system is.

The header tank has a VW pressure cap and is the blue one in the lower right of the photo. There is no sign of any discharge from the cap at all - it's all clean. Unlike old rad systems, there is no pipe from the pressure cap. The cap and header tank and swirl pot is standard TVR set-up.

I am beginning to suspect I have an air lock in the short stretch of top hose and currently there is no way of bleeding it - I've just ordered a bleed adapter. I suspect the pump is pushing some water through and is, of course, sucking some via the rad bottom hose and that's why the rad is working. If there is an air lock, then the water will churn and effective flow rate will be small causing the block to overheat.

To me the logical step is to now fit the bleed valve as that's easy. I am also making up a jockey wheel so that will ensure the pump won't slip and be a better set-up anyway. After that it's on to the pump itself, cleaning the block and possibly pressure but I don't currently think it's those.

I'll post when the bleed valve is fitted.

[unstable load]

I am going to take a stab and say one of your airlocks is at about an inch or 2 to the right of the jubilee clamp on your top hose.

As for circulation, if your pump is submerged and there are no restrictions in any of the hoses to the pump, it should move water as advertised. The air in the system creates hot spots and the compressibility of the air effectively allows the water to boil, none of which are good.
An air free system with a pressure cap raises the boiling temperature over 100 degrees C and coupled with an efficient, up to spec cooling system will maintain the working temperature of the engine at the desired level.

[DaveEFI]

On my SD1 EFI, it's not uncommon to see 100C on the gauge - indeed that is the middle marking on the gauge. Usually at very slow speeds on a hot day. At more usual speeds it reads between 80 and 100. The thermostat for it is an 88C type.

So I'd be inclined to see it it 'tops out' at round about 100C, rather than stopping to let it cool. If pressurised to the normal 15 psi, it won't boil until 115C or so.

FWIW, I don't think it's possible to make a cooling system which stays at exactly the same temp when hot. They all have a range for 'normal'

[richardpope50]

Water comes out of ECU sender port (highest point that's easy to check) and swirl pot and rad are all full so I would agree there must be an air lock as said.

All temps are from the MegaSquirt calibrated reading in TunerStudio as my gauges are not accurate. If the temp would go down sometimes such as when the fan comes on then I would be happy for a temporary 100 reading but it only goes up. I have got to 105 and bottled out there. I can drive about three miles at gentle pace and it gets to 100.

Bleed valve ordered so will see......

Thanks.

[mgbv8]

Why is there a swirl pot in the top hose?

[DEVONMAN]

Why is there a swirl pot in the top hose?

It appears to be TVR's way of dealing with the fact that the rad and header tank are lower than the engine due to a low front bonnet line.

I suppose under racing conditions, the odd bit of air developed as a result of local boiling of the coolant or cavitation will get trapped in the swirlpot and at the next cold start the air will get expelled to the header tank.

I think a simply 8mm TEE off the top hose at it's highest point would do the trick provided the top hose enters the rad through a straight neck without the down loop.

[mgbv8]

Why is there a swirl pot in the top hose?

It appears to be TVR's way of dealing with the fact that the rad and header tank are lower than the engine due to a low front bonnet line.

I suppose under racing conditions, the odd bit of air developed as a result of local boiling of the coolant or cavitation will get trapped in the swirlpot and at the next cold start the air will get expelled to the header tank.

I think a simply 8mm TEE off the top hose at it's highest point would do the trick provided the top hose enters the rad through a straight neck without the down loop.

If the swirl pot only has one small vent hose i guess it must go to a sealed expansion tank somewhere? I cant see that being able to easily get rid of trapped air to be honest.

I agree that the top hose straight into the rad with a tapping from the high point into the exp tank would be better.

[DEVONMAN]

The swirl pot will only get rid of trapped air during the warm up process at which time it will force air through the coolant in the low level half filled header tank and out through the pressure cap.

Unlike the simple TEE idea, the pot has a larger capacity for trapped air and will allow normal system flow even when a reasonable amount of air is trapped during any one event.

I have run a TVR and the swirl pot system did work but I did think it was a bit ott and Le Man rather than necessary.