VR Engine Bay Residual Heat

[oneohtwo 8]

Has anyone ever had much success with reducing the residual heat in the VR6 engine bay, or given much thought to it short of cutting large holes in the bonnet? We all know it gets pretty hot under there, small bay/large engine etc, but after coming home the other day having just been driving around pretty slowly I popped the bonnet but could barely touch the bonnet stay it was so hot. Obviously having been going so slowly no airflow could build up and eject the hot air, but even so. I imagine they are designed for the temperatures but nevertheless all that heat can't be tremendously good for the components in there.

 

Best I could really think of was wrapping the exhaust (odd thread in here on the subject), the aforementioned vents in the bonnet and stripping the sound proofing off. I even was thinking of some sort of cowling around the fan/radiator with a pipe running over the gearbox and venting under the car perhaps... I think it could be done, and if the piping is designed well may even improve airflow through the radiator!

 

Anyone else given it any consideration? I'm sure no one really wants to go cutting up a perfectly good bonnet, but thought it might make a good discussion point!

[seanl82 23]

Tons of options. Mocal Oil cooler, fan upgrade, rad upgrade, lower temp thermostat, removing the cover parts on the grilles that have them, wing vents (Merc Sprinter) etc etc.....

 

You can go nuts if you want, but the cars are now at the point where standard is looked upon as best. As long as your cooling system is working correctly with water level sitting around 90, and oil around 100-115 and the fans coming on in stages at the correct temp then there shouldn't be any problems.

[a_riot 0]

You can go nuts if you want, but the cars are now at the point where standard is looked upon as best. As long as your cooling system is working correctly with water level sitting around 90, and oil around 100-115 and the fans coming on in stages at the correct temp then there shouldn't be any problems.

 

I would agree. I had the same issue but couldn't find anything obviously wrong. But it turned out there were a number of small things wrong that added up to excessive heat in the engine bay cooking plastic parts and hoses, etc. Typically these aren't obvious issues and missed so low temp sensors or low thermostats are used as a workaround, but that just shifts the problem, and now things run too cool in winter etc. A properly working Corrado typically doesn't run too hot except under extreme situations.

 

Make sure you have the proper coolant with the right ratio filled to MAX and the system is bled. I use distilled water and G13 these days.

Make sure you are using the proper oil viscosity. Higher oil temps will lead to higher coolant temps.

Make sure your fan's 1st speed is coming on and going off at the appropriate temperature. Normally my fan won't get to 2nd speed unless stuck in traffic on a very hot day, but make sure all 3 speeds come on and go off when they are supposed to.

Make sure the thermostat isn't sticking closed and opens fully when it should.

Make sure the temp sensors are the correct temp values and working. You can get higher valued sensors and tstats as well as lower so make sure a PO didn't do something like that.

Make sure your radiator is working efficiently, is clean and there's nothing blocking it between the condenser and radiator and has the cardboard strip sitting on top of it to prevent circular air flow.

Make sure the aux water pump is running when its supposed to.

Make sure your reservoir cap isn't leaking pressure before its supposed to.

Make sure your head gasket is good and combustion isn't getting into the cooling jackets increasing pressure/temps in the cooling system.

 

If all that works, you shouldn't really see high coolant temps under normal driving conditions but expect some variation from Corrado to Corrado. I have 2 and one runs hotter than the other for reasons I can't figure out. I suspect that the cooler running one has slightly less timing after having the head decked when doing a head gasket, but that's just a theory. But I did notice it ran cooler when the HG and timing chain guides, but also installed a new radiator at the same time. If yours is original it may be time to replace it.

Edited September 19, 2018 by a_riot

[oneohtwo 8]

Fair points all!

 

Although I wasn't so much getting at the engine temp itself, mine is sits around 90, oil around 100-115 so the cooling system is doing it's job well. It's just all the heat from inside the engine pretty well gets dumped into the bay, from the rad, around it and has nowhere to go. I was thinking of all the other parts that sit in the bay outside the block that might not like it.

 

Taking it to an overly simplistic level, i's almost the situation where there better your engine cooling system is, the hotter the rest of the bay will get - all that heat removed from the engine has to go somewhere, and the more that is removed the hotter it, wherever it is, will be... So the things mentioned above, whilst improving the engine temp won't help the rest of the bay! Maybe it's not a problem, just anything excessively hot doesn't feel comfortable!

[a_riot 0]

Taking it to an overly simplistic level, i's almost the situation where there better your engine cooling system is, the hotter the rest of the bay will get - all that heat removed from the engine has to go somewhere, and the more that is removed the hotter it, wherever it is, will be... So the things mentioned above, whilst improving the engine temp won't help the rest of the bay! Maybe it's not a problem, just anything excessively hot doesn't feel comfortable!

 

That's not quite correct though. The heat from the engine is supposed to be passed into the coolant and radiated out the radiator by using the fan, not just radiate into the engine bay and stagnate. If sitting in a traffic jam air can get trapped, but once moving it should dissipate, but it is a small engine bay with almost 3 litres of motor so there is that.

 

Is the cardboard deflector at the top of the radiator and all the radiator air ducts still in place (see image)? Air flow can be tricky, and if hot air is getting trapped in your engine bay, that might be why. You can use smoke to see what might be going on with the air flow inside the engine bay but that often tossed piece of cardboard prevents the air from endlessly cycling around the radiator, so its not as useless as some think.

 

The air is pulled rearward into the engine bay but once moving should leave through the bottom and sides and not saturate the engine. Even if your temps are ok though, that doesn't mean that everything is fine, as it could be the fan is coming on more frequently than it should to try and keep temps normal, when normally it wouldn't run as much, thus pulling more hot air into the engine bay even though temps are fine.

 

If the fan isn't coming on when it should, heat will build up and then as soon as the engine is saturated with heat, it won't cool down until the motor is off. This is typically seen with fans that have lost the 1st speed, or have a Chinese thermoswitch that doesn't switch it on at the right temp. I had that happen, and opening the hood after driving resulted in a blast of hot air in the face. Once the engine is heat saturated due to a cooling issue, there's really no way to cool it down without turning it off and waiting.

 

Check to make sure all your heat shields are still in place as well. If you have a laser heat device, you can try pointing it at various places to see what is going on and maybe make changes if need be. Maybe something as simple as an air duct that directs the fan air downward might help, just make sure it doesn't overheat some other component like the battery, etc.

[oneohtwo 8]

That's not quite correct though. The heat from the engine is supposed to be passed into the coolant and radiated out the radiator by using the fan, not just radiate into the engine bay and stagnate. If sitting in a traffic jam air can get trapped, but once moving it should dissipate, but it is a small engine bay with almost 3 litres of motor so there is that.

 

Yes, indeed this is it really - I was being overly simplistic just to illustrate a point and it shouldn't really be an issue when moving at a decent speed. It is just the sitting in traffic and moving slowly, which seems to be an increasingly common occurrence! I don't think the fans on their own have enough to force it out under the car and as you say once it is saturated there's not a lot to be done.

 

I don't have the card section on top of the radiator though, that is something I need to rectify. the old radiator I had never had it, and I don't remember if the new one came with any - might have accidentally discarded it as packaging. Will need to sort something out there. I guess that must happen pretty regularly!

 

I do wonder how much difference an airduct at the back of the radiator would make, behind the fans. Always seemed a sensible idea to have the radiator in a separate compartment, if nothing else from an air resistance perspective.

[Dox 23]

That's not quite correct though. The heat from the engine is supposed to be passed into the coolant and radiated out the radiator by using the fan, not just radiate into the engine bay and stagnate. If sitting in a traffic jam air can get trapped, but once moving it should dissipate, but it is a small engine bay with almost 3 litres of motor so there is that.

 

 

Hot air rises, the bonnet is only sealed on the rear edge so heat will leave via the bonnet to wing gaps and via the grill when the fans aren't running. The bonnet itself will act as a heat soak radiating the heat into the atmosphere.