3.0 V6 Overheating - exhuast manifold related?

Justin85 · #1 (**permalink**) 05-19-2008, 11:17 AM

Hi,

I know this is a common topic but I have a 1987 3.0 V6 which overheats when driven hard for any period of time. I have started using the car for trackdays and although it runs just fine in normal road use and when idling, when we really push it on track it overheats fairly quickly, with steam coming from the expansion tank.

I have removed the thermostat, checked fan operation, removed and flushed the rad and engine and it still seems to overheat. I do not think it's the HG as there are no other signs of head gasket failure and it doesn't over-pressure straight away.

The exhaust manifold developed a leak about the same time it started to over heat. However, as this was our first trackday in the car we're not sure if it's related. But it did seem that as the exhaust leak got worse, the car overheated quicker. Could it be that with the exhaust manifold leaking ignition has become advanced somehow and the car runs hotter?

Many thanks,
Justin.

AR4me · #2 (**permalink**) 05-19-2008, 12:53 PM

My money is on the engine pressurizing the coolant system. A leak may be so little that you don't see signs during regular driving. I have had a very similar experience. You can get a little kit that can check for exhaust gasses in your coolant - simple and cheap. This condition can occur without you seeing oil in coolant or coolant in oil.
Jes

**papajam** · #3 (**permalink**) 05-19-2008, 01:08 PM

Running without a thermostat can actually cause overheating. The reason is that without a stat, the coolant velocity through the radiator is so fast that the coolant has insufficient time to cool.

Depending on the severity of the exhaust manifold leak, there may not be enough backpressure. This could result in a weak mixture which, because weak mixtures burn hotter, may be the root cause of your overheating.

AR4me · #4 (**permalink**) 05-19-2008, 01:26 PM

Quote:

Originally Posted by papajam

Running without a thermostat can actually cause overheating. The reason is that without a stat, the coolant velocity through the radiator is so fast that the coolant has insufficient time to cool.

75evo · #5 (**permalink**) 05-19-2008, 02:59 PM

I think AR4me could be correct. Check the cap first.

slyalfa · #6 (**permalink**) 05-19-2008, 03:16 PM

the V6 is a bypass system. the bottom of the thermostat has a 2nd ring that valve closes the bypass while the big valve opens the path to the radiator.
if you just remove it you would need to plug the bypass some how or else you are not going to get very much flow to the radiator.

**papajam** · #7 (**permalink**) 05-19-2008, 04:01 PM

Quote:

Originally Posted by AR4me

I have run the Alfa V6 (albeit a 2.5) in race conditions without a thermostat without any issues whatsoever. I don't believe this is an issue.

AR4me · #8 (**permalink**) 05-19-2008, 04:22 PM

Jim,

I'm glad to hear you are concerned about my engine wear. You'll be equally glad to learn (I hope) that it only ran like that shortly due to an "emergency", but it doesn't change the fact that I saw no issues whatsoever - laws of physics and all.

Anyway, each to his own - don't think this is helping Justin much.

Jes

**papajam** · #9 (**permalink**) 05-20-2008, 07:48 AM

You're absolutely right, Jes. My apologies to all if my response seemed a bit..........abrasive.

ToonRboy · #10 (**permalink**) 05-20-2008, 02:16 PM

I had an exhaust leak once (on my 3.0 - seems to be a common problem), but it mostly heated-up the starter & brought fumes into the cabin. My overheating problem started the first time I flushed my cooling system (on my Gold model). After thinking about it for a while, I noticed that brass bolt on the thermostat housing. After loosening it a bit, a lot of steam hissed out. I ran the car up to temp again and bled it one more time till only coolant came out. Problem resolved.

Be careful to put a hand towel over it when you loosen it (so you don't get sprayed) and not to torque it down too much as you can split the washer, or worse, the thermostat housing.

oldschooleuros · #11 (**permalink**) 05-26-2008, 02:51 PM

A few things to keep in mind:
I didnt see if you said this.... But did you pressurize the coolant system to check for leaks?
Does the coolant hose look good? Is it closing under pressure because of age.
From experience and seeing this happen, this is the first thing to do, and I am kinda shocked nobody mentioned this.
Open the rad cap, start the car. See if the coolant rolls (is moving around) in the rad. If it is not, the waterpump is most likely not working properly, or at all. That is certainally a death warrant for a motor.
Did you run it hot? If so, say goodbye to your HG.