Insulating headers/engine bay temp

I have noticed, since fitting my 1776 into my crossover and monitoring oil temps, just how hot the rear tin gets. I have an EMPI header mated to a Bugpack box and even when I had the 1641 engine it got hot enough to fade the paint on the rear valance (it's a shite paint job to be fair...).
I was wondering about insulating the headers from the surrounding tin. I don't really want to use exhaust wrap as that will just hold the heat in the heads so I was wondering if anyone has used a reflective foil/insulation type solution attached to the tin and valance to keep the heat from soaking into the engine bay?

Yes did one a few years back. Just used those spring clips riveted to some light gauge aluminium. Worked on the same principal as a double roof on a Landrover.

It had no effect on engine bay temperature when running since it wasn't much above ambient anyway but it did keep the rear valance from getting so hot from the four into one header.

Ps, your right about wrap.

Hmm, so you're thinking it's not worth the effort except for a piece by the valance?

I've only ever owned the a bus with a 4 branch header so I don't know what it's like with a standard exhaust but the rear tin is too hot to put your hand on after a good run. I bet you could fry an egg on there! I had figured that it would introduce some heat back into the engine bay but is the principle that you have so much ambient air rushing in while moving that it doesn't get a chance to get heated?

I took a motorway run of about an hour on Wednesday; a hot summer evening. I cruised at 3800 rpm (occasionally going to 4000 to pass lorries quickly) and the temp rose steadily to 240f or maybe a snadge beyond it. The oil temp sensor is mounted in the Type 3 dipstick hole so I'm thinking it it is in the best place for most accurate temps. Oil pressure stayed at a healthy 40 psi (now that I've upped from 0w30 to 20/50...) but you mentioned in another thread Trikky that I should "start to worry at 240f". Is it OK to cruise at this "alarm" level or is it the time to pull over? At no time did the engine performance seem to change and when I pulled over I could hold the dipstick (not comfortably but didn't have to let go).


Dropping down to 3000rpm the temp stabilised at around 220f and at all other times the temp stays comfortably below 220

Yes the large air flow through the engine bay means it doesent get all that hot in there when driving.

However, I would be getting worried with oil temperature at 240F (which is 115C). It's not critical failure but it is rather hotter than normal unless the engine is having to work very hard like climbing a long hill in hot weather.

If you are still able to hold the dipstick at such indicated temperatures then it would suggest your gauge may be reading high. Any chance of borrowing an infra red gauge to check against yours perhapse?

If after checking the accuracy of your gauge, your oil temperature really is getting to 240F on a regular basis, then something may be making the engine run too hot ie. wrong ign timing, missing tins under the barrels or lean mixture for example.

(Retarded ignition timing and mixture faults can both also cause the exhaust to run hotter than normal but it is common for the rear valence to get pretty hot with a four into one).

Thanks Trikky, that's interesting...

I don't know of anyone with an IR gauge I could borrow but I have thought about draining the oil, pulling the sensor and dropping it in boiling water with the ignition on. Should give an accurate 100 degree reading.

There are a few things that may be causing it to run hot though...

1. I have been struggling with fuelling and jetting since building the 1776 and getting a bum steer on jet sizes from a reputable supplier (see my other thread). I am currently running the same Idle jets and venturis as when the engine was in 1641 form but with slightly larger mains (I have twin Kadron 40s). With the larger Idles and venturis I was supplied it just wouldn't run smooth or pull/rev properly so I had to go back to the current configuration which seems to work well/miles better. Could be that things are a bit lean though? I'll pull the plugs to check.

2. I'm finding timing to be a bit of a dark art, in so much as if I set the timing to 40 degrees max advance, vacuum disconnected at full throttle, then there isn't enough advance to stop the engine faltering on in gear acceleration. So currently I have what appears to be "too much" advance for max throttle in order to get smooth running under general driving. Could this cause hot running?

3. You might recall that I built this engine in an aluminium Auto Linea case and it is my suspicion that aluminium doesn't conduct heat away as well as magnesium alloy.

All the tin is definitely in place, including the little bits under the barrels; I remember having to take off the newly fitted and nicely torqued up heads with perfectly adjusted tappets when I found them sitting on the bench during the rebuild!

It's all been a bit of a long journey to get this far since the rebuild and I'm happy to just be using the bus in anger again but clearly there's more work to be done...

Ah yes I remember now

I would have thought your case would conduct heat just as well as the magnesium alloy stock ones if not a little better - but I am guessing here because I have no experience with an autolinia case. If there were such a problem I am sure it would have been all over the forums long ago.

Yes the testing of your sensor in boiling water should at least tell you whether its right at 100C. Having tested a few of these in the past I would suggest you use an electric kettle on an extension lead so it actually boils the water with the sensor in there. I was using a cooking thermometer to monitor the kettle and found that in the time it took to get from the kitchen to the garage the "boiling" water had already cooled to around 88 by the time I got the sensor and its earth connection in there - even if I ran Lol.

As for the timing - did you make a typo? The dissy should go to max 28 to 30 BTDC vac hose off. With the vac hose connected max advance will go to around 34 ish. 40 is way too much even with the hose on, let alone with the hose off.

If your dissy is working correctly then this setting should give you around 7 to 9 degrees at tickover.

If your engine prefers to run at an indicated max 40 degrees advance then its likely that either the timing marks on the pulley are wrong or the timing light is faulty. A normal dissy, if set to max 40 degrees, hoses off, would give you around 17 degrees advance at tickover. This would make it run pretty badly and it would be difficult to start, with the engine tending to kick back against the starter.

Yes the plugs would be a good way to see if its running lean.

I am hopeful its your temp gauge reading too high.

Yes a late night typo! I meant 30 degrees vac off It starts on the button to be honest so hopefully not too advanced but it still would be on thick side of advanced I reckon (assuming the timing marks are good as you say).

I'll check the temp gauge/sender and plugs first I think and see if I can't track down some slightly richer jets.

Thanks for your help Trikky

Zcat7 said:

I was wondering about insulating the headers from the surrounding tin. I don't really want to use exhaust wrap as that will just hold the heat in the heads so I was wondering if anyone has used a reflective foil/insulation type solution attached to the tin and valance to keep the heat from soaking into the engine bay?

Click to expand...

I've not done this on a bus but I have had some expierience with race car applications and there are several options available that would transfer over....

Heat wrap:

No it wont increase the temperature of the heads and if applied properly will reduce the amount of heat lost into the engine bay from the exhaust monifold quite drastically.

Ceramic coating:

You can have your manifold ceramic coated which will stop it soaking up as much heat from the exhaust gas which in turn results in less being passed in to the engine bay. It works reasonabally well but isnt cheap so you need to do the cost vs reward calculations to see if you personally think its worth the expense.

Reflective heat proof tape:

Cheap, provides a physical barrier and also helps reflect the radiated heat plus it can also be aplied accross holes and joins in tin to block unwanted air flow from the hot side. I've used it on a formula four racer before now quite effectively. Completely stopped the damage we were getting to the bodywork/paint.



To be honest I'd combine the exhaust wrap with the reflective tape and not bother with coating as you could be completely done in a couple of hours but I'd look at why its getting so hot first as all youll be doing otherwise is masking a potential problem.

Hope my 10c helps

Rich

Would it be worth trying to duct air to this area must be worth a punt

Some nice ideas Rich. Ceramic coating is probably going to be too expensive, especially without looking into the underlying cause first. I had thought about heatproof aluminium tape. I've used this before to good effect but am skeptical that my flaky/oil tinware will hold it for long.

I think this would be a difficult area to duct air into Tristan as it already has the outflow from the fan blasting past it underneath.

I think its best in all to address the core heat problems; check the gauge/sender for accuracy and set the timing and fuelling on a rolling road. I messed with the timing a bit over the last couple of days and advancing too much caused an alarming rate of heat buildup! I quickly pulled over and retarded the timing and things cooled straight back down to about 233 on the gauge. Ambient temp was cooler than the hot running example before though. I noticed at this retarded setting that I began to get stuttering again with in gear acceleration so I either have the wrong advance curve or wrong fuelling. Possibly both...

Will check some more tomorrow.

Have you checked inlet manifold temps are roughly the same

I haven't. Could hold my hands on and get a rough idea. What's your thinking?

You can normally get a indication if a side is running lean or hot if there's a big difference in the two you know it's probably mixture