Intermittent heat (Harry Metcalfe, you out there?)

I think there is air in the cooling system and when less rpm the air prevents the water from circulating. had this on a lotus once

 

may be the waterpump impeller is damaged and so less water will get circulated in the system?
do you you see at the temperature gauge a difference between the heating works and not works?
is this "no heating" problem only when you drive with low rpm or also when the car is standing and idling? if so what will happen when you raise the rpm when the car is standing?
if you have an infrared thermometer you may check the temperature at the 2 radiators top and down and also the heating hose going to the front.

you mean for sure the shop has refilled and then evacuated? evacuated on all 3 bleeders?

what also could be that the heating hose coming from the engine may be bent/snapped off somewhere?

 

Another failure mode is crud blocking your heater hose flow. My heater hoses were disintegrating on the inside so I replaced them.

 

may be they used a wrong size impeller?

how many rpm you need to get heat?

 

my car use to do this. the thermostats get lazy. They will open at 190-195 but never really close until the engine is cold again. So when I would drive when it was cooler out, the the engine temp/coolant would go right down because there is still coolant going through the rads and not recirculating through the engine and heater core. Change them both. Easy job. You don't need to take the engine out
Barry

 

Jay535, a couple of thoughts. Did your mechanic orient the new thermostats with their bleed holes pointed to the top of the thermostat housing to vent air? See picture below. In a hot water bath, my 1986 TR original Savara 9.10.358.00 thermostats just "crack" open at 160 and 169 degree F and are "fully" open at 180F. They will start to close below 180 degree F. Were your new thermostats tested by your mechanic to be in spec before installation? The Ferrari Owners Manual, page 59, also gives specs for thermostat and cooling fan temp operation. EDoug

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Harry and barryr are describing the symptom as the water temp gauge reads low so heating is feeble. Is your water temp gauge also showing a low value when you get the "no heat" condition, or is your heat coming and going suddenly with the water temp gauge always reading ~195 deg F?

 

I am going through this with my 512tr currently.

Before I noticed the problem, I drained and replaced my coolant. I created a vaccum w the harbor freight tool to refill my system. I thought this was the best way.

Afterwards I noticed what you are encountering. I then bled the system with the normal bleed screws and really saw no more air.

However, I did notice that my car would not get up to 195F when I drove it in the cold. This makes me believe that one or both of my thermostats are bad.

I have purchased new ones but have not had time to put them in. I’ll happily report what I encounter.

This is probably even more important on the 512tr because the computers will keep trying to enrich the fuel trim.


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That is a very unusual situation, and the first report of such an issue that I can recall. The default of the TR hot water valve (if the HVAC system loses power) is to be full open so we often have had reports of heat when not wanted/requested, but not the other way around. A couple of things you might try:

1. Perform the resistance tests at the unplugged HVAC ECU connector described on pages H29 and H30 of the TR WSM -- could be some (wacky) input sensor value is causing the HVAC ECU to intentionally close the hot water valve when it shouldn't. If all those are OK,

2. Next time you want heat, and it goes away, unplug the hot water valve in the passenger footwell behind the passenger footrest, and see if heat returns -- would verify everything with the physical hot water flow is working correctly (if the hot water valve was open). If it does = then things like bad HVAC ECU, or maybe something wacky with a relay/connection on the HVAC unit itself = don't want to go there!

Good Hunting!

 

It's on the RH side of the compartment behind the passenger foot rest. The two pin connector on the top (with the brown and brown-white wires) just pulls off upward (and has no polarity requirement, IIRC, so either way is OK):

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My thermostats were upside down with the air holes in the 8 o’clock position.




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https://youtube.com/shorts/3zq7VdFaPqY?feature=share


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Lol…sorry it wasn’t more exciting!

That honestly was what I saw for the first time. My 512tr has had 3 engine services in its lifetime by authorized dealers so either 1) anyone can make a mistake or 2) the bleeder hole orientation doesn’t matter that much? You can also see that those are original thermostats by the little plugs used in the bleed holes.

I just wanted to show you guys what I saw.

I still plan to pull the heater electro valve in the cabin and make sure it is clean while the coolant is drained again.


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Confirmed today that the thermostats were bad.

First, both of the originals were opening much too early.

Second, one of them stuck open as it cooled. It’s easy to miss if you really don’t look for it.

Both of the new ones remained shut and opened fairly sharply around 82c. They also close SIGNIFICANTLY faster when removed from the hot water.

It feels great when you positively find the problem.

Now comes the fun part of putting it back together.


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That is supposed to be closed after cooling….but you can see that it’s still open.


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Happy you found that. Same behaviour as mine before I replaced them
Cheers
Barry
New doesn’t always mean good.

QUOTE="tf308, post: 148606663, member: 2880"]Confirmed today that the thermostats were bad.

First, both of the originals were opening much too early.

Second, one of them stuck open as it cooled. It’s easy to miss if you really don’t look for it.

Both of the new ones remained shut and opened fairly sharply around 82c. They also close SIGNIFICANTLY faster when removed from the hot water.

It feels great when you positively find the problem.

Now comes the fun part of putting it back together.


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I was able to get everything back in the car today.

Car will now get to 195 from an idle and the heat now works.

A few things that I learned

1) You will spend some time laying on your exhaust and engine. It’s pretty close to water boarding after a while.

2) A pair of “coolant hose picks” Astro 9502 on Amazon made life easy. I would just cut the hose at the start.

3) Dielectric grease lube made the installation easier.

4) The 45 degree angle of the valve assembly is so frustrating when you go to reinstall.

5) it’s not fun, but it is possible with the engine in the car.

Lastly, if you have 3/4 inch hose you can test the function of your heater valve. You can blow through it with the key off, but mine closed %100 shut as soon as you turn the key to on.


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