Overheating 350i

[Pilo-Wedgebits]

Hi guys,

Went a run out with Hotty at the weekend in the new toy she sat a indicated temp of 50 degrees (which I thought was a bit low) The minute I hit traffic the temp shot straight up. I have an override switch inside so a got the temp back down ok apart from when I lifted the bonnet she was pushing water out of the cap. I have a new cap ready to fit and I'm going to change the coolant pipes at the weekend along with the thermostat but any ideas what it could be? I was going to flush the rad and the block through whilst I'm at it.

Cheers

Shaun

[honestjohntoo]

Pilo-Wedgebits said:

indicated temp of 50 degrees ---- hit traffic the temp shot straight up ---- override switch got the temp back down ---- lifted the bonnet she was pushing water out of the cap

Without that override you are close to meltdown. Could be leaking head gasket, crud in system or simply just airlocks. Suggest urgent review/overhaul to clean out crud, observe for bubble stream and refill without airlocks.

o Drain the system.
o Check stat/cap are to spec, hoses secure, etc.
o Forward/reverse flush rad, block and matrix with garden hose at domestic water pressure.
o "Coolant Fill without Airlocks" by using this process. Click Here
o Look for a constant stream of bubbles in the expansion tank due to head gasket leak pressurising cooling system.

To avoid wasting coolant and to practice the process, perform no-airlock refil with plain water, bring to temperature, observe for leaks, bubbles, stable cooling performance, etc. Correct any problems discovered before coolant refil without airlocks, again.

[hallsie]

honestjohntoo said:

Pilo-Wedgebits said:

indicated temp of 50 degrees ---- hit traffic the temp shot straight up ---- override switch got the temp back down ---- lifted the bonnet she was pushing water out of the cap

Without that override you are close to meltdown. Could be
To avoid wasting coolant and to practice the process, perform no-airlock refil with plain water, bring to temperature, observe for leaks, bubbles, stable cooling performance, etc. Correct any problems discovered before coolant refil without airlocks, again.

Hmmm, wish I had thought of that before rushing in too quickly and pissing bright green coolant everywhere!!!

[Pilo-Wedgebits]

Head gasket gone - need I say anymore

[HOTTY]

Pilo-Wedgebits said:

Head gasket gone - need I say anymore

But it ran to Melton OK ?

Oh sh8t Shaun, whats your plan ?

He must have sold it knowing the bd

Are we going to get the tools out I will give you a hand if you need it.

Stephen

[Pilo-Wedgebits]

Hi mate,
Thanks for the offer - she is currently sat in a mates garage awaiting attention. Do you know how big a job it is? He has quoted me 250 inc skimming heads - would have a go myself if fairly straight forward tho.
Cheers Shaun

[adam quantrill]

Why do they always say they want to skim the heads. Just bung on some composite gaskets, it's not hard to do either. The trickiest bit I found was cracking open the head bolts, do them a little at a time and you should be OK.

P.S. my 350i still bears a scar on the windscreen surround where the 3 foot breaker bar I was using on the last head bolt swung round when it let go with an almighty "crack" ;^)

Edited by adam quantrill on Wednesday 7th April 13:26

[RedRum350i]

Thanks for the good tip on filling the system HonestJohn.

Had successfull first outing of the season at Croft on Monday - first 20 pointer! Probably due to suspension improvements. However, had coolant problems again:

1. Running on the road, coolant level seems fine, now that we've got proper seal on all the caps.
2. Runnning on the track obviously pushed the temperature up, which resulted in the overflow tank filling beyond capacity (aparently the cloud of steam as it gushed onto the exhaust in the second chicane was quite spectacular!)
3. The run home resulted in temperature being quite eratic - lots of hills and bends sending the temp up. Does that indicate an airlock?

Q1 Should I fit a larger reservoir so I don't have to keep emptying for events/filling for the road?

Q2 According to the SD1 tip - how do I "rock the car a little" with new stiffer suspension?

Cheers

Steve

[Wedg1e]

adam quantrill said:

Why do they always say they want to skim the heads.

Here here. The RV8 heads (and the blocks) date from the days of sand-casting when large amounts of alloy were poured in. They can withstand huge amounts of heat without distorting, unlike modern cars where with CADCAM techniques the heads have as little alloy as possible resulting in distortion and cracking. Thin-wall casting is why cracked heads are so common nowadays.

[honestjohntoo]

RedRum350i said:

Thanks for the good tip on filling the system HonestJohn ..... Runnning on the track obviously pushed the temperature up, which resulted in the overflow tank filling beyond capacity .... The run home resulted in temperature being quite eratic - Does that indicate an airlock?

Cheers! No question! The lost coolant was replaced by air when the engine cooled down during/after the event. Thus it exhibited the classic airlock symptom - variable temperature.

Instead of adding capacity to the pressurised system why not capture the expelled coolant, feeding the expansion tank overflow pipe to an unpressurised overflow container (Tesco - Flat Plastic 0.5 - 1.0 ltr Shampoo bottle - no lid) strapped somewhere adjacent but below the expansion tank. The expelled coolant then sits there, dumb and happy, until the engine starts to cool down, creates a vacuum inside the cooling system which then sucks it all back in instead of air, thus preserving the prior status of the system, IE, no air locks.

Its gets even better! If you keep the overflow container part-full, the system automatically keeps itself topped up. This is mentioned in a different context (minor head gasket leak) in the last paragraph of this web page

[carob]

Bigdaftlad (AKA) Roy had a similar set up to the one mentioned on the Rusty Nail Run last year, although his was a tonic water bottle it worked a treat.

Rob,

[RedRum350i]

Thanks for the advice. There is an overflow tank below the reservoir - I presume this is meant to be doing the same job as you describe with the pop bottles? It was this that filled during the race - the plug in cap had popped so I think it was that that spilled the fluid onto the exhaust. I kinda understand the logic about the vacuum effect, but now on 3rd pressure cap on the reservoir, and it still doesn't suck back. What else am I doing wrong?

Cheers

Steve

[honestjohntoo]

I never had that situation when the fluid did not suck back, but bear in mind my reason for the installation was to work around a minor fault condition - small/almost insignificant, head gasket leak.

Suggest three possibilities.

o The cooling system de-pressurises before it cools so no vacuum is generated.

o The overflow tube is cracked, or not in the bottom of the tank.

o The pressure cap is too high pressure. I had 15 psi.

It also begs the question, why did the coolant pop out anyway? On a perfect system with the expansion tank half filled, coolant expansion is not supposed to overflow. Otherwise the cars/engines would never have left the showroom.

Maybe you have a more fundamental problem such as:

o Minor head gasket leak that occurs under maximum stress.

o Trapped air somewhere else in the system - Matrix?

o Cooling system capacity insufficient for the thermal load.

. o Rad core undersize for a V8.

. o Cooling fans inefficient.

. o Viscous coupling not working proper.

. o water pump cavitating.

Edited by honestjohntoo on Thursday 8th April 12:52

[RedRum350i]

Thanks HonestJohn

Just had the Rad recored, so hopefully it's not that. I'll try a new pipe from the reservoir to the overflow tank - I'll let you know if that works (cap is 15psi).

With regards capacity, that was what led my limited logic/knowledge to ask about a larger reservoir. If anyone has successfully sourced and fitted a bigger one, could they share the details?

Plan C will prbably be (a) empty reservoir to minimum when I arrive at event, and (b) fill it up again before I head home.

Cheers

Steve

[adam quantrill]

What sort of cap do you have - it's not one of mine is it? My ones have a little brass plunger underneath the bottom seal that opens to allow the suckback, and a top seal too to keep the sucking effect focussed on the overflow pipe leading to the catch tank (or pop bottle).

A lot of 350i's don't have a catch tank but just waste the coolant onto the ground - not very satisfactory.

[GV]

I had the same cooling problems until I had the rad re-cored. Went from 3 to 4 rows and since then my temp always stays constant. I will also add that since converting to carbs - there is less heat soak due to the absence of the plenum.

Otherwise the correct filling of the rad and heasder tank on level ground will go a long way to sorting the problems. I also plumbed in a bleed valve on the heater return pipe just make life easier in getting rid of any trapped air...

[honestjohntoo]

hjt said:

Cooling system capacity insufficient for the thermal load

I think my choice of the word "capacity" was misleading! What I meant to say was its ability to dissipate heat. The size (capacity) of any non circulating expansion tank or overflow facility would make no difference.

Hence the suggestions
. o Rad core undersize for a V8.
. o Cooling fans inefficient.
. o Viscous coupling not working proper.
. o water pump cavitating.
being fundamental to the system's ability to dissipate heat.

Regarding your re-cored rad, I found out to my cost that there are different types of rad, 2, 3 and 4 row (core?), each having progressivley more cooling fins. Not saying your rad is not good, just suggesting in extreme conditions, size matters.

My erstwhile Vdp Efi used for holiday caravan and other heavy duty stuff was wrongly fitted with a new 2 core unit by the PO and in some conditions it was simply inadequate.

[Pilo-Wedgebits]

Omg garage called today - they snapped off a head bolt in the block. Composite gasket turned up with big split in it. Old gasket completely shot on both sides although the rest of the engine is tidy. Should have bought a moggy minor - any tips Graham

[blaineuk]

not good shaun, hope you get it sorted.

[350zwelgje]

A good garage can sort a bolt problem without any issues, due to experience, and knowning the alternative to helicoiling it...

Rob