86 Prelude Questions

[Damiano]

Hi all, I'm a relatively new owner of an 86 prelude with some wear and tear on it. I've been working on different parts here and there, but I plan on completely fixing the thing up and I'm not super sure on most of the processes, as my experience fixing cars is rather limited and I don't have easy access to people that could help.

The primary thing right now is that my car is heating up pretty quickly whenever it idles, but the moment the car is moving it cools down within moments. A few weeks ago I had to replace the tubes for the coolant bypass (pair of two-inch long tubes right in the middle of the engine compartment) as they had ruptured, and until the last couple days or so the car's been fine. Is it possible this could be related? I've been trying to research the issue and it some people are saying it could be a coolant blockage or leak (though I'm 100% positive it's not a leak on any of the lines, I've checked multiple times to make sure), and others are saying that it might be something to do with radiator fan or the thermometer that manages when it comes on. Next chance I get I'm going to idle the car for a bit to check and see if the fan is coming on, but otherwise is there anything else I should be checking?

Also, whether or not this is the case, any tips on checking for blockages in the first place? I have no idea the process to check for this without taking things apart.

[Dr_Snooz]

Welcome Damiano. It sounds like the cooling system has been neglected. Rusty colored coolant would be confirmation of that. Take some time to do a serious inspection of the cooling system. You changed the main hoses, but check the multitudinous smaller bypass hoses that go all around the engine bay. If they are hard and cracked or soft and spongy, they need to be replaced. If you have numerous bad bypass hoses, it's best to replace them all at once or they will start bursting at the worst times.

As for the blockage, you can try a couple different things. What I would do first, is to remove the thermostat. Stick a garden hose in the hose end of the thermostat housing and turn it on fast. Water should flow out the cylinder head. If you get water blurbling out around the hose and not out the cylinder head, then you can suspect a blockage. While you have the garden hose out, flush all the old rusty water out of the cooling system before putting it back together and replace the old thermostat with a new one. It's cheap insurance.

Another way to check is to remove the radiator cap (NOT while the engine is HOT!!!). Start the car and watch the water circulate into the radiator. If you see lots of turbulence, or no flow at all, you can suspect a blockage.

Yet another way to check is with an infrared thermometer. With the engine hot, take temperature readings at various spots on the radiator. A big change in temp indicates the location of a blockage.

Remember that a blockage can also be caused by a bad thermostat (that's why you should simply replace it) or an old rubber hose that collapses when hot.

It's rare for these cars to heat up just idling and I haven't heard of them having a lot of trouble with radiator blockages. By contrast, the cooling fans do have lots of failures, so you're right to start by checking there.

[knifemind]

While you're at it, replace the radiator cap. I ended up swapping my radiator, fan, thermostat, and sensors before i figured out it was just a bad radiator cap.

[Damiano]

Alright, found one of the two cooling fans is not running at all, period. I've got a checklist of things to replace (couple of tubes, the thermometer, and a few wires too) but most importantly I'm also going to be replacing the radiator as there's a hairline fracture in the thing. Turns out almost everything in here is stock parts so its a wonder the thing has still been trucking along so well. As far as the radiator replacement goes though, I ran into a little confusion. Turns out it's an '87, somehow missed that on the registration, but I was wondering if there was any real difference on the radiators between the '86 and the '87? Found a few deals, but wanted to run it past you guys before I ordered any parts.

http://www.autopartswarehouse.com/sh...ator-1986.html
Murray Heat Transfer 433933 - Radiator | O'Reilly Auto Parts

[knifemind]

86 to 87...There should be no difference at all. I dont think theres any [radiator] differences at all from 83 - 87, but if there are any, it would not be significant.