Overheating related explosion

[ACJJ619]

I'll try to keep this brief but I don't wanna leave out any details.

I have a BMW E30 with an M52 engine swap. The temp gauge has never worked cause the temp sender was never installed but it's always been fine.

Yesterday I took the drain plug out the radiator, let it all drain, then filled the tank up with new coolant/water mix. Today, I drove 15 miles. There was a little bit of steam out the back but I put that down to not driving the car much at all in the last few weeks and the cold weather just building up condensation in the engine. After 15 miles, the steam was quite bad out the exhaust and it began coming out the engine bay, with a bad smell and poorer running. Clearly overheating basically.

So I pulled over and let the engine cool down. I figured air had got into the system during my coolant change. I ran it with the cap off and kept topping it up with water whilst it bubbled and gurgled until I felt warm air coming out the vents, and the fan was coming on and off. It seemed to be working fine now that I'd got the air out.

I drove the next two miles to my job interview and the car seemed to be running fine. As I parked up - WHOOSH. Big explosion of steam from the engine bay. No pop or crash as such, just a big whoosh. I tried burping the system as before and running it with the cap off but I couldn't seem to get any warm air from the vents.

I then found a leak from the bottom of the radiator. Difficult to say specifically where yet as it was dark, but there is water leaking out the bottom. I guess that's what the explosion was.

So, it's all very well replacing the radiator and stopping the leak, but I need to know **why** the explosion happened so the new one doesn't do the same thing. Would the initial overheating have weakened it so when it came up to operating temperature and pressure it just failed? As I said, as far as I could tell it was working fine before those two miles once I'd burped the system.

[Brianmoooore]

Chances are you ran it air locked after the coolant change, and may have cooked the engine. The M52 isn't noted for giving you a second chance.
BMW black plastic cooling system components are notorious for going brittle with age, so the pressure surge from then overheating may just have finished a weakened radiator off.

[ACJJ619]

The thermostat and (metal) water pump were brand new when the engine went in a few months ago so they should be good. The radiator was second hand so could have failed under the stress of the overheat.

The engine did seem absolutely fine in that short two mile trip between overheating and the steam explosion so I'm cautiously optimistic that the engine isn't cooked (too bad at least). I just don't want to replace the radiator only to find the issue lies deeper than just a weakened radiator.

[Motorhole]

Seen a few people claiming to be running without a working temperature gauge recently - it's just not worth the risk! For the cost of a cheap sensor and some simple wiring.

A new rad, fit the temp gauge, get it re-bled and hopefully you don't have any head/head gasket issues

What kind of rad is it? The integrated expansion tank type or the external type (i.e. M3)? If the former, the bleeding process is to fill from the top hose until coolant comes out the rad, then attach the hose and top up. Run the engine up to temperature (with heaters & fan on full) then take for a short drive, all with the cap on. On your return, switch of the engine and let any remaining air bubbles out the bleed screw.

Filling and warming the car up with the front of the car raised can help ensure that the bleed screw is the highest point on the circuit and therefore where the air should collect.

Have followed this process a few times (first fill,busted rad, busted heater valve) on the same setup and never had an issue.

[Brianmoooore]

The thermostat and (metal) water pump were brand new when the engine went in a few months ago so they should be good.

Google "bathtub curve".

[ACJJ619]

Okay an update. Sorry for the length - just trying to give as much info as possible.

Yesterday I replaced the radiator for a new 328i one - same as before. With the expansion tank on the side and the larger of the two models.

To start I topped it up with water and started the engine with the cap and bleed screw removed. It's difficult to know operating temperature without a gauge but I ran it for about 10 minutes or so with the bleed screw removed and just kept it topped up so water was coming out of the bleed hole slightly. It was bubbling for a while and seemed to settle down so I turned the engine off and put the bleed screw and the cap back on. I was getting hot air from the vents but interestingly the electric radiator fan doesn't seem to have come on.

The following morning (today) I had a look and the water level had dropped slightly so I topped it up and took it for an easy 5 mile round trip, with a 10 minute rest in the middle at the 2.5 mile mark. Engine sounded and felt fine although I didn't push it, and there was hot air from the vents as before. Again though, nothing from the electric fan? I've tested the fan by connecting the two wires together and it works, so I'm not sure what's up there. Maybe with the cold temperatures and strong winds at the moment it simply isn't required for the amount of time I've put on the engine?

So after letting it cool down from this morning I ran it again just now. This time I took the cap off and ran it for 15 minutes with a thermometer probe in the expansion tank to monitor the temp of the water near the cap opening (I guess this is where the hot water from the engine enters?). After 15 mins the water level had risen to almost overflowing, the thermometer was showing 40c, there was hot air from the vents and the fan again didn't kick in. I tried to keep the bonnet down as much as I could but it was open for a fair amount of time so as I said before, I don't know if the strong cold winds at the moment are just cooling the radiator down enough that the fan isn't required but I'm just not sure. The top hose was hot but not too hot to hold and the bottom one on the opposite side of the radiator was cool and easy to squeeze.

If I bought something like this: http://tinyurl.com/osnfzur which temperature sensor would I need to insert into it?

Also, are there any other ways you can suggest for me to test the various components and system? The thermometer I have is this: http://thumbs4.ebaystatic.com/d/l225/m/ ... NmH2oA.jpg

[Brianmoooore]

If I bought something like this: http://tinyurl.com/osnfzur which temperature sensor would I need to insert into it?

You know what the temperature is in the top hose - it's printed on the thermostat. If it's any higher, you have a problem, and need a mechanic, not a gauge.
The first thing you need to do is to fit and ordinary E30 'brown' sensor in the side of the head, and connect it up to thye standard gauge.
The next thing you need to do, is to fit a thermal switch in the boss on the RH side of the radiator, part way down (where it can monitor rising radiator temperature), and connect it, via the relay positions provided in the fusebox, to the electric fan.
Coolant does not flow through the header tank in any meaningful quantity, so you will not measure engine temperature there.

[ACJJ619]

"You know what the temperature is in the top hose - it's printed on the thermostat." Sorry, I don't follow. Are you saying that the top hose only fills with water once the thermostat opens at 88c? So I guess I can rule out a dodgy thermostat considering that hose gets hot?

I was expecting to see the temperature on the thermometer rise more to be honest and I was going to see if it surpassed 88c. I guess that's when the fan should cut in? I don't know - when should the fan cut in?

Until I get a gauge would I be right in thinking the fan is my best bet of making sure it isn't overheating? I would assume if I see the fan come on and then go back off, it means it's detected rising temperatures, lowered them to something sensible and switched back off again - meaning the engine is then at a safe temperature. I'm not 100% on how the fan has been wired but it's something to do with a Volvo system. Before all this happened it seemed a little eager to come on, actually. It would often turn on a minute or so after I'd parked and turned the engine off and remain on for a further minute or so.

I can't see down there because the intake is in the way but someone else with an M52B25 on a stand said he had a look and there isn't a spare hole to put the brown sensor in? So I don't really know what to do about that.

"thermal switch in the boss" Sorry, you've lost me. I'm useless with cooling systems. Ask me something about suspension

Is it worth testing the temperature switch in the side of the radiator somehow? I'm assuming the electric fan is a fairly straightfoward wiring setup - when that switch detects a certain temperature it closes the circuit and turns the fan on. So the fact manually closing the circuit activates the fan makes me think either a broken switch or the water simply isn't getting hot enough. I saw somewhere that the switch works by pinging out voltage and reading the return voltage, which changes depending on the temperature of the water. Would the fact it's purely water instead of coolant change the way it works?

EDIT: I just thought of a way to test the switch, fan and wiring. If I unscrew it from the radiator and submerge it in boiling water, it should trigger the fan, right? If it does, we know the switch, fan and wiring are working correctly. If I did this, would I need to re-bleed the system?

[ACJJ619]

I just checked the oil filler cap and there is mayo in there, but considering the engine has run three times today for short bursts and cooled in between, it could just be condensation so I'm not going to jump to conclusions on a head gasket or cracked head. I know it doesn't always affect the running but as previously stated, the engine does feel and sound as smooth as before so I'm not going to jump to worst case scenarios.

Also, when I idled it for 15 minutes earlier there was a reasonable about of steam coming from the exhaust initially but it then died down, which I think goes along with my condensation theory.

[BenHar]

Have you looked at this? http://www.e30zone.net/e30zonewiki/inde ... emp_Sensor

Ben

[ACJJ619]

Of course, although I can't see down there because the intake is in the way. Someone else with an M52B25 on a stand said he had a look and there isn't a spare hole to put the brown sensor in? So I don't really know what to do about that.

[bosers]

Gotta say fella, mayo and steam is a bad sign. Engine shouldn't accumulate condensation that quickly. Hope you get it sorted

[ACJJ619]

After extensive research, I believe the 2.8L had the blanking plug but the 2.5L like mine doesn't. I think what I'm going to do instead is use the port for the throttle body coolant line as I don't live in cold enough conditions to warrant having that. I'll rethread the sensor and stick it in the throttle body coolant port next to where the blanked port should be. Then I'll block off the other end by welding it shut like this: http://i.imgur.com/r6cDLpa.jpg

Regarding the fan not coming on yet - I've also found out that water is actually better at carrying heat away than coolant. The coolant is only there to prevent freezing and raise the boiling point, but it's the water which takes the heat away. I'm thinking maybe because of the cold temperatures, strong winds, 100% water, large high quality radiator and on-the-safe-side thermostat has meant it simply hasn't got hot enough to warrant turning the fan on yet. It's possible that it's just doing a really efficient job of cooling I guess.

[pianist]

The coolant is only there to prevent freezing and raise the boiling point.

To lubricate the pump and prevent corrosion too

[DanThe]

Antifreeze does not just stop freezing, it stops the insides of the engine rotting away, you would be mad to run without it.

When the M52 came out they originally had three threaded holes in the side of the head the same as the M50, although the M52 uses a double temp switch rather than two separate switches like the M50 used so you would often find the middle hole blanked off on early M52's. As production moved on and changes were made they did away with the redundant middle hole.
Common practice is as you say, to turn down the thread on the E30 brown temp sender so it fits the throttle heater outlet which is the rear most hole of the three

[ACJJ619]

Ah so I may have a blank hole if my engine is early enough. We'll see I guess.

So you know what size I need to rethread the sensor to? I've seen 12mm x 1.75 and 12mm x 1.5 mentioned.

[DanThe]

The same as the thread thats on the outlet stub you remove

Its fine 12mm so M12x1.5

[ACJJ619]

Okie doke, thank you! I've had a pretty extensive search around the procedure but nobody actually talks about the wiring side of it. Would you mind explaining a little about this? Once I've screwed the sensor in, is there just a plug on the loom I've gotta find and plug into the back of the sensor?

[Brianmoooore]

Amongst the four wires going to the existing coolant temp. sensor are a brown/yellow and a brown/purple. These are the wires that connect to the now redundant half of the sensor that work the E36 temp. gauge.
You cut one of these wires as close to the plug as possible, and connect it to an E30 temp. sensor plug with a short piece of wire connected to it. This will be a brown/purple wire, so it's usual to connect to the brown/purple in the M52 loom, and leave the brown/yellow where it is. The joint should be soldered and insulated with heat shrink sleeving.
You temp. gauge should then work, once the sensor is fitted and its plug attached, assuming the brown/purples were connected correctly at the engine loom C101 plug.

[ACJJ619]

Sounds relatively straightforward, although electrics are probably my weakest point! The loom was done using a simple adapter like this: http://e30elektronik.325ix.com//cache_b ... apter0.jpg

Thanks for all the help, chaps.

[Brianmoooore]

Inelegant (and by the prices I've seen, a very expensive) way of doing things, but I would expect the brown/purple to be connected through that.

[ACJJ619]

Seemed like a really tidy, easy and cheap way at the time! £45 I think it was and the engine bay looks really tidy to my naive eye. I've had one guru say it looks really tidy and OEM too so maybe I just got lucky The chap I had do the conversion did a really great job so maybe it's more down to him than the adapter

[Brianmoooore]

The chap I had do the conversion did a really great job

????? He left you without a temp. gauge!

[DanThe]

Do u drift man?

[ACJJ619]

Ergh. Drifting.

[ACJJ619]

Todays update:

For the record in case it's relevant - I didn't use the car yesterday. There was no mayo on the oil filler cap today and no sign of oil/water mixing on the dipstick or in the expansion tank. I ran the engine for a few minutes and admittedly there was steam coming out of the exhaust for the first minute or so, but then it died down to nothing at all for the next few minutes. Completely clear.

I did notice the top radiator hose seemed to be warming up gradually rather than staying cold for a few minutes and then suddenly getting hot, so now I'm thinking perhaps the thermostat is stuck open? I guess this would also explain the fan not coming on, although the vents do get hot-ish. Not as hot as I remember they used to get, but I would say they're on the hotter side of warm. Weirdly, it only seemed to be the top of the hose that was getting warm. The bottom of the hose was stone cold. How on earth could the top of the hose get warm and the bottom stay cold? That defies physics!

I think my next plan is to run some K-Seal through the system before giving it a new thermostat and proper coolant. I know the opinions are mixed on K-Seal so there will no-doubt be people on here who hate the stuff but I've read enough credible success stories to believe it's worth a go. Considering I'll be emptying the system out again to give it proper coolant, I won't be leaving the stuff in there for long so it won't bung up my system or anything in the long run.

I'm going to pick up a brown temp sensor too when I get the K-Seal. I'm not very confident about removing the intake manifold and wiring it all up so I'm hoping a local friend can become available in the next few days to help me but if not I guess I may be forced to do it myself. I'm going to avoid driving the car properly until I have that gauge working but until then if I NEED to do an occasional 2 mile journey, the properly bled system, K-seal and new thermostat should keep me going until I can get that gauge working so I can properly diagnose whether it's running cold, perfect or hot.

I'm going to buy a compression tester in the next couple of weeks when I get some money (don't you just love a broken car when you're between jobs) so I will be checking the condition of the spark plugs when I perform that.

Once again, thanks for all the help and advice.

EDIT: I've just been to have a look where the sensors are in the block, and the access isn't as bad as I thought it would be? I can see very clearly the two ports and where the blanked one should be, and I think I would be able to remove the throttle body port and stick the sensor in without removing the intake manifold.

Interestingly, the top hose is now warm all the way around, as opposed to the top being warm and the bottom cold as it was when the engine was running. This makes me think it was just warm air entering the hose from the engine, hense the top getting warm and the bottom being cold.

[Brianmoooore]

I ran the engine for a few minutes and admittedly there was steam coming out of the exhaust for the first minute or so, but then it died down to nothing at all for the next few minutes. Completely clear.

Perfectly normal. Every litre of petrol you burn produces about nine litres of water, This is emitted from the exhaust as visible steam until the exhaust system gets hot enough to keep it vaporised until clear of the tail pipe. It's still coming out after this, but you just can't see it. BMWs are worse for this than cheaper makes, because of the substantial amount of metal in their exhausts that has to be heated up.

I did notice the top radiator hose seemed to be warming up gradually rather than staying cold for a few minutes and then suddenly getting hot, so now I'm thinking perhaps the thermostat is stuck open?

Again, perfectly normal. The initial warming of the top hose is by conduction and leakage through the 'stat. When the coolant around the 'stat reaches its opening temperature, it opens, allowing hot coolant into the hose.
Top hose being hot, and bottom hose cold, shows that the radiator is doing what it's supposed to.

I think my next plan is to run some K-Seal through the system

DON'T!!

I'm not very confident about removing the intake manifold

Really easy job on the M5x engines. All the nuts are easily accessible with 1/4" or 3/8" sockets, and the gaskets are reusable.

[ACJJ619]

Good to hear a few 'perfectly normal' diagnosis' there. Right now I guess there's more evidence to suggest the engine is running okay than not, which is encouraging. Although I'll reserve judgement until I get a working temperature gauge and can drive it properly.

I was expecting backlash for the K-Seal plan! So go on then - what's your opinion? I've seen lots saying it's evil and clogs up the whole system and I've seen lots say it worked a treat. One chap used it with great success on his $12,000 racing engine and was able to abuse it for over a year!

I have just edited my post with an update, but here it is for ease: I've just been to have a look where the sensors are in the block, and the access isn't as bad as I thought it would be? I can see very clearly the two ports and where the blanked one should be, and I think I would be able to remove the throttle body port and stick the sensor in without removing the intake manifold. Although the wiring and sealing of the disregarded throttle line could be fiddly.

Interestingly, the top hose is now warm all the way around, as opposed to the top being warm and the bottom cold as it was when the engine was running. This makes me think it was just warm air entering the hose from the engine, hense the top getting warm and the bottom being cold initially.

[ACJJ619]

I'm just not sure it will. It's only 250ml - in the grand scheme of things 250ml in a 10L cooling system surely won't create major issues? It reacts chemically to the change in pressure and temperature where cracks and leaks are present and solidifies there, much like how scabs work in humans. It's not a thick gunk circulating the whole time. Besides, I'll be draining it in a week or two when I put proper coolant in. Can't hurt to run K-Seal around for half an hour beforehand? It can have a go at sealing any small cracks or leaks there may be and if not it'll get flushed out anyway.

[DanThe]

The only permanent part is the mucky sludge that it turns into permanently in your engine/heater matrix/radiator/waterpump etc etc. You can flush it as many times as you like but you will never remove it all once its been put in