328 running hot at low speed

Keep an eye on it. I went through this whole scenario a little over a year ago, same symptoms but got progressively worse as time went on. I started with new radiator cap, new hoses, new radiator, new water pump, easy bleeders and auto bleeders but in the end it was head gasket.

While going through all this I must have read every thread ever written about it going back probably ten years and I learned a lot about the cooling system of the 308. The 328 has a number of improvements but basically is the same. I’ll have to warn you there is a lot of misinformation out there and one of them is the “sucking air in” myth. I never could get that figured out because as the coolant cools and the volume decreases it can’t suck anything in since the fluid in the expansion tank is higher than the rest of the system so if air gets pulled in through the overflow it just stays there at the top of the tank.

As I said before I’m not claiming you have a blown head gasket but here’s a simple test that will give you a quick answer. Remove the cap from the expansion tank (when cold) start the engine and look in there with a flashlight. Do you see a steady stream of coolant flowing in from the upper bleed hose or do you see a constant stream of air bubbles? If you see bubbles, you’ve got a problem.

Also, forget the auto-bleeders, they don’t work. Ask me how I know....

 

ONE thing I have to admit I've wondered about occasionally, especially with all the posts about this subject is: It is possible for the water pump or other system characteristics to cause cavitation and actually "make" air in the system. DD two strokes required a specific coolant package to prevent "micro-cavitation" and its subsequent reduction in cooling. Seems unlikely here since that didn't happen when these cars were new, so if air keeps showing up in the system. it's because something is...as they say in scientific circles... broken.

But cavitation can be caused by changes in the system over time - like corrosion in engine water system passages, radiators, etc. So MAYBE there is something to the claims that air really is "generated" in some of these cars as they age due to system changes caused by cavitation, which, MIGHT be caused by insufficient coolant additives over time. ???

NOTE: This is just "thinking out loud" on my part...

 

Cavitation does not generate air. It creates coolant vapor which will condense back to liquid when the coolant temperature drops or when the local pressure in the coolant rises above the vapor pressure. Vapor pressure is temperature dependent. Liquids boil at the temperature where the vapor pressure is equal to the local pressure. The local pressure in a cooling system varies due to changes in the velocity of the coolant through small passages, etc, thus lowering the pressure and causing cavitation. Micro bubbles can form on surfaces as a result. This bubbles don't necessarily get swept away by the liquid coolant and can result hot spots because they reduce heat transfer which, over time, can damage liners. I have heard reports of damaged liners from cavitation but I have never met anyone who actually suffered such a fate.

 

Thanks John! I didn't know that cavitation "bubbles" were vapor which condenses back to liquid. Clearly this debunks my speculation re the possibility of air being "generated" and we go back to the scenario that "if there's air in the system that needs regular bleeding, something's broke"

 

I don't think the formula is a factor; AFAIK, green Prestone is pretty much the same now as 1985, give or a take a minute percentage of additive.

 

It's all basically the same, pumps, turbines, boat propellers.... If the fluid pressure drops below the vapor pressure at some point in the flow path, vapor bubbles are generated. As you note, they can cause significant damage in different ways. In turbines and pumps it's primarily by erosion. (Like you, years ago I was involved in design of turbines and pumps associated with power generation.) In IC engines it primarily a problem with engines with wet liners (AKA Ferraris, etc) where it effects heat transfer in addition to errosion.

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There's a 0.9 bar and 1.1 bar pressure cap available for these. Was the cap replaced like for like?

 

Not sure if this was addressed already, but do you have the foam barriers installed? (I have a 308 , not sure if the design on the 328 is the same, but the foam barriers forces the air to move thru the louvers instead of getting "stuck" on the spare tire compartment)

 

As far as rad caps, rather than fooling around, in the US I suggest buying the cap Ricambi sells. Yeah, it cost more than going to Pep Boys and buying a rad cap for 6-8 bucks but from Ricambi you'll get the functionally correct cap, not one that just happens to fit but doesn't work correctly in the application. Nothing wrong with the Pep Boys cap per se, but it's the wrong design for an expansion tank; it's fine for a radiator with an overflow tank but that's not what we have.

 

Have to disagree, Mike. Just take the old cap to any auto parts store and ask for a similar one with 1.1 bar rating and you're good to go. The only thing you need to check is the depth. NAPA 703-1698 works just fine. It's the same construction/design as the OEM cap. This radiator cap crap is way over analyzed.

 

Good point! I'm sure you can find a correct cap but, from my own experience, selecting a cap by saying you want a cap for a 328 Ferrari or using the list they have at the parts store for cars/rad caps, got me the wrong cap for the car. Only issue with taking your current cap and matching is that it assumes the current cap on the car IS the proper type of cap. As long as you know it's the proper cap, I agree you can match it.

But it is important to have the cap with the proper return vent design (spring loaded shut). The most common type of cap is wrong for the application. Using it, the cooling system won't pressurize properly (if at all) and, as a result, it will regularly spit coolant overboard, eventually causing the coolant level to be low enough to create a problem.

 

I guess that's an advantage of being an original owner. I was able to take the OEM cap with me. The problem was two fold though. The OEM cap was cracked, thus leaked and would not hold pressure anymore. But it was also a 13 0.9 bar cap. So I replaced it with a 0.9 bar cap which would still, on occasion, allow some coolant to piss out. Changed to the 1.1 bar and that solved the problem. The NAPA 703-1698 would appear to be identical to the Stant 10231. Both are vented 16 psi caps and apparently have the correct depth for the Ferrari expansion tank.

I think what you are referring to are the caps with the little thing that dangles and requires the coolant to expand and push it closed. Yes, they won't work on our cars. We need the Type A cap, not Type B. It's a jungle out there.

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Too Funny! That Stant cap per internet cross reference "Is not suitable for your 1989 Ferrari 328 GTS"

I'm Not saying it's the wrong cap, undoubtedly if he who must not be named uses it, it's right. Just pointing out NOT to trust general application information.

 

The only way to suck air through the expansion tank is if you let the coolant level get too low and the tank is empty.
But my 328 did have a habit of sucking air through an improperly sealed radiator bleed screw, until I replaced it.
A gap in the system anywhere can cause both coolant to leak out (running) and air to enter (on cool down).

I like to cold bleed my cooling system by putting a few psi of pressure on top of the reservoir tank with a hand pump, to both facilitate the bleed and to confirm that the system holds pressure.
Of course, without a specialty cap with air hose, putting pressure over the tank involves layers of plastic and a boatload of rubber bands -- a real Rube Goldberg kludge.

But I've found that doing a pressure bleed on my 328 (with the heater cores open) makes for a "one and done" bleed.
FWIW

 

Mityvac MV4560 Cooling System Pressure Test Kit
About $35 Good enough for DIY.

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Don't pressure test over 10-12 lbs.... More than that and you might cause leaks.

 

To clarify: coolant flowing into the expansion tank from the upper bleed hose is completely normal. What you don’t want to see are air bubbles in that flow.

I’ll also warn you that the block test kit is inconclusive unless you have very badly blown head gasket and you can somehow get a test on the system when it’s hot. Not sure how you would do that because it’s impossible to remove the cap when it’s under pressure. I did indeed have a failed gasket that was leaking at the #4 cylinder but I was never able to get a positive result from the block test, which I had to perform after it had cooled enough to open the system, it always showed negative and the fluid stayed blue.

 

Here are two short videos I took last year. The first shows the air bubbles in the stream and the second shows how I located the source at #4 cylinder when doing leak down checks.