Engine overheats, when air con turned on

[tomtaylor1]

Hi All, on my Nissan SR20 DET, LPG, Mazda RX8, when I turn on the air con, after around 5 mins the engine gets hot, rising from around 80/84 to 95/100,not running the turbo, so have to turn off the air. Head gasket recently replaced, due to overheating, this overheating issue is now fixed. Now even when thermostat removed, the engine overheats with the air con on, so have to turn it off, then engine quickly returns to 80/84. large twin electric cooling fans and radiator fitted.

Have not used the air con in the last 6 months due to it needing to be re-gassed and having a number of botched repairs.

Air repaired same time as the new head gasket.

Driven at 120kph, air off the engine temperature does rise to around 92/94.

The temperature of the water is registered on a Defi Zd advanced multi function gauge, the temperature is taken from where the water enters the top of the radiator, or is it leaves the radiator.

Thank you in anticipation.

Regards Tom

[lust]

Sr20 turbo swapped rx8 running LPG. What a nightmare that thing must be for troubleshooting.

[tomwct]

Replace your cooling system!

[daveAustin]

Aircon pump, radiator bunged up, cooling system pressure loss?

[tomtaylor1]

Hi, I flushed out the radiator, the radiator is hot all over it's surface, not loosing any coolant, over 1500 kms.

Thank you.

Tom

[JAS21]

So your cooling system is marginal ... and the added heat from the air con is just too much.

You could try a new or high capacity water pump ... you must have already looked at the water pump ... yes?

As you have already flushed the radiator with no success ...try an acid clean ... no success ... fit a new or bigger one.

[Lancashirelad]

Hi, I flushed out the radiator, the radiator is hot all over it's surface, not loosing any coolant, over 1500 kms.

Thank you.

Tom

Did you back flush it? i.e. from bottom to top. Wrap a piece of rag around the end of your hosepipe so it forms a (more or less) seal as you push you the hosepipe into the bottom outlet then wait for clean water to run out from the top outlet. Sounds like a new rad is required. Can you easily see through it? Are all the fins intact? Photo?

Is the bearing on the AC compressor failing and causing severe drag?

[pgrahmm]

Is it physically overheating or just a gauge reading? 100c is 212f.....With coolant a pressurized system can go to about 260f.....

Of course the engine is taxed about 15% with AC use so is working harder with higher engine compartment temperatures so some increase is to be expected.....

[FrankGers]

Might be an electrical signal that is causing it

[sirineou]

The cooling system was adequate for the original engine but marginal for the swamped engine. The additional strain of the A/C putts it over the edge.

since the water pump is from the swamped engine I will assume it is adequate. I would look in to fitting the car with a higher capacity radiator

[pgrahmm]

http://www.superchevy.com/how-to/project-cars/sucp-1204-cooling-system-basics/

Good info here.....food for thought....

[DavisH]

I guess a bigger radiator is required? After I modded my mini (overbore, race pistons, cam, etc), the stock radiator would nearly cook if I got stuck in traffic.

[scoutman360]

I have solved this exact same problem many times by buying a new radiator. This was in the U.S. where new radiators don't cost that much more than a rebuilt or recore. No experience in Thailand, though. Flushing, recore, acid tank, etc. is a gamble. New one always solved my over heating problem. If your car has an extra fan that is supposed to turn on with the A/C, check to make sure that is working.

[tomtaylor1]

Thank you for all the information. the radiator I flushed with acid, the cooling fans are from an XR7, both fans are running continually, will look into a high capacity water pump, also will back flush the radiator, all the fins are intact.

Would the radiator cap have any effect on the cooling system, should I fit one with a higher weight.

The spark plugs are running a light grey colour.

Regards Tom

[canthai55]

A new cap would not hurt, but judging by the symptoms I think the rad is just undersized. Altho if the water pump impeller is old, and the vanes are not close to the pump body, it will turn alright, but will not pump much water. Me, I would look at a larger rad, and when it is changed also change the pump. New cap for a new rad is a given. Along with all the hoses and thermostat

[pgrahmm]

Thank you for all the information. the radiator I flushed with acid, the cooling fans are from an XR7, both fans are running continually, will look into a high capacity water pump, also will back flush the radiator, all the fins are intact.

Would the radiator cap have any effect on the cooling system, should I fit one with a higher weight.

The spark plugs are running a light grey colour.

Regards Tom

Yes - you can upsize your radiator cap & the more pressure the more efficient the system should run - in theory......

KEEP IN MIND THOUGH - Every component in your system is engineered for the manufacturer's set pressures....Once you exceed that safety limit at the cap you run the real possibility of blowing out another part of the system.....

I did this on a car once with a car that overheated on grades - went ok until I went up a long harsh grade = popped an expansion plug at the back of a new head - cost me a tow & repairs......

[Daffy D]

Would the radiator cap have any effect on the cooling system, should I fit one with a higher weight.

Yes! the radiator cap keeps the system pressurized and therefore makes for lower temperatures.

Check the radiator cap to see if it's original pressure rated. Fitting higher pressure cap would also help,

Are you sure the new head gasket is doing it's job properly?

[lust]

Are you sure the fans are spinning the right direction?

[lj cm]

Are you sure the fans are spinning the right direction?

That is actually a valid question.

I bought a used car, and while it did not overheat, the Aircon was not cold, when the car was not moving.

I checked the fans and one (of the two) was blowing air out instead of in.

I switched the wires and everything was OK.

[tomtaylor1]

Hi All, thank you for the info, have back flushed the radiator, no debris flowed out, just some slightly dis- co-loured water flowed out.

The same symptoms still occur running petrol or LPG, as I said before the radiator is a large one.

Think the next step is to have the water pump checked again, and look into to a high capacity pump.

The engine bay does get hot, the radiator for the air con, sits in front of the radiator.

Regards Tom

[sandgroper2]

Is it automatic, if so, dont drive in drive, drop it a gear, problem fixed.Also, if youve taken the thermostat out , how is the cooling fluid going to stay in the radiator long enough to be cooled???

Edited June 24, 2016 by sandgroper2

[norbra]

Also a good idea to refill complete system slowly to prevent air locks in your engine block and head. Air locks tend to increase engine bay temps significantly, Also can cause fuel to vaporize in feeder pipe

Edited June 24, 2016 by norbra

[Linden]

Check air con fans are blowing the correct direction...with all the mods easily done fans all fighting against each other.

Thers obviously nothing physically wrong with the engine

Temp sender should be on the closed side of the system close to thermostat housing

Giving a temp before stat opens..if fitted

[Linden]

Check air con fans are blowing the correct direction...with all the mods easily done fans all fighting against each other.

Thers obviously nothing physically wrong with the engine

Temp sender should be on the closed side of the system close to thermostat housing

Giving a temp before stat opens..if fitted

[paddyjoe41]

First check that the rad cap is not blocked,then i would back flush it,then if not good it sounds like a bigger or at least a new rad,

[billphillips]

You may want to check that your rad fluid is coolant and not just water. The boiling temp of coolant is higher than that of plain water. Your motor is not too far over temp but it could be caused by low coolant system pressure. Having said that as the motor seems to be rather non standard ... It could be anything.

[Brock]

It could be that several of the cores are blocked, so not enough cooling area for the non standard engine.

The fuel mixture may be to lean, so that will cause a hotter burn, and raise the engine temperature.

Having the thermostat out can cause high coolant flowso not enough time to cool the radiator. The aircon will pump hot air over/through the radiator, so will raise the temp., that is normal.

You need to address the engine heating issue and forget about the aircon.

[crutchy26]

OK. Here goes. A/C 'radiator' sits in front of engine radiator. it's the first to clog-up with bugs/critters & dirt.

A/C off no pre-heating of incoming cooling air.

My guess is you need to split the radiators, spray in some De-gresaer from the ENGINE side (maybe some dishwashing liquid). THEN hit both 'radiators, from the engine -side, hit the rads with high-pressure -small nozzle water, to flush out the air-grills.

Happy motoring

[sead]

Sometimes i don't believe what I'm reading. He did write LPG right? That engine is famous for errors and oil consumption. It's a boxer and i hope you have been to a professional who advised you to put LPG on a boxer turbo engine.

[sead]

Took me 3 min to know that an RX8 first runs very hot to then go down to cooler temps. Do you have soft valves. LPG on a twin turbo boxer. You are asking for problems.

What kind of engine is least suitable for LPG conversion?

The worst kind of engine for LPG conversion would have badly designed (soft) valve seats which will not resist Brinelling and Friction as well as harder seats would. In addition, it is known that the more similar the metals that make the valve heads and seats are, the more Microwelding will occur. Weight of the Valve Head and Stem is also as important as the hardness of the valve seats. An engine with 3 or 4 valves per cylinder is more likely to resist VSR than an engine with only 2 per cylinder, although if those 3 or 4 valve seats are soft, there will be no benefit. If the engine does not have hard valves it is wise to begin by having the valves re -engineered to the required standard using parts made of much harder material (often 'Stellite'). In addition, an engine with single helical valve springs will suffer more Erosion due to Valve rotation than an engine with two opposing helical springs would.

Can an Engine with Hard Valve seats be damaged?

Valve damage can occur when running on any fuel.

If the valves are made to run too hot due to incorrect fuel/air mixtures this may make Brinelling and resulting VSR much more likely. Incorrect fuel/air mixture, especially if too weak, can overheat the valves, resulting in accelerated Brinelling. It is important for the correct mixure to be supplied to the engine whether it is being run on Petrol, LPG or any other fuel.

Fitting Harder (normally Stellite) Valve Seats

This needs the services of a specialist engine re-manufacturer (re-conditioner). It is a wholly seperate business, requiring a large investment in machinery and the skills required. We cannot offer this service and it is unlikely that any other LPG conversion company will be able to do so. If you decide to go ahead with conversion of an engine with soft valve seats it would be best to begin by having this work done prior to conversion. A search for local engine re-manufacturers (perhaps in Yellow Pages or on the internet) would be the way to go.

In Conclusion

It would be incorrect to heap all if the blame for VSR on LPG.

If an engine's valves are truly fit to run on modern unleaded petrol (for any reasonable length of time) they are good enough to run on LPG with no additional problems, and it must be remembered that all of the effects described above still occur when running an engine on Unleaded Petrol, especially if the valves have been 'engineered down to a price'.

The plain fact is that ALL engine valves will reach the end of their useful life at some point. Nothing lasts forever, although valves with harder seats made out of quite different material to the head and stem assembly will definately last longer when running on any fuel, as will desmodromic valve arrangements.

Finally, note that most modern LPG systems depend on the car's original [petrol] fuelling system to deliver the correct mixture at all times, e.g. if the petrol system delivers weak mixtures that is a problem in itself, and will be translated directly into weak mixtures when running the engine on LPG simply because the LPG system is doing what it is told to do by the petrol system. In a case like that, the LPG system and the installer cannot be held responsible - it is an ordinarly (as if it were unconverted) car maintenance issue, not an LPG issue.