I have a 1994 Del Sol S (1.5L) I purchased last month. The engine seems to take FOREVER to warm up and doesn't stay warm. Outside temp about 25F, it'll take about 5 miles for the needle to move up to the C mark, takes 10+ miles before I get heat, and about 15 miles to get to almost midway on the gauge. Any deceleration at all and the temp drops back down.

I thought it might just be a stuck thermostat, so I replaced that (with a 180F thermostat from Advance Auto), and it doesn't seem to make a difference (the one I removed was a 170F). I figured with such a small engine it should be able to warm up pretty quick, but it seems like any drive less than 30 minutes and it never warms up. The idle does drop when it makes it up to the C mark, but I don't get heat for a while more.

Is this normal for a Del Sol to have such a problem warming up? Is there something else I'm missing here? If it just took a while to warm up I wouldn't be as concerned, but the temp dropping under deceleration doesn't seem normal. Car is all stock, 110k miles.

 

cut a piece of card board half the size of the radiator and put that infront of the radiator. see if that makes a difference. These ld15b7 engines run super cool for some reason. My d15b7 wont put out any decent heat without the radiator blocked off. One thing I did to help the heat was to take out the blower motor and blow out that area with an air compressor. It didnt make the engine run hotter, but it did make the heater work a little faster and my temp gauge still registers just a tick below half way

 

Thanks for the suggestion. I did order a factory Honda thermostat I'm going to put in once this rain system ever ends. It does EVENTUALLY warm up to just under half on the temp gauge, and the heat will roast you alive when it does. It's the part where the engine cools under deceleration (way before the tstat should be opening) that has me feeling off.

 

I thought I'd update for anyone with a similar situation. As many other threads have indicated, the aftermarket thermostat was the culprit. The thermostat I removed was aftermarket, the one I installed from Advance Auto made no change. The Honda thermostat (roughly $35) resolved the problem. Engine now warms up quickly and stays warm. About 2 miles after starting my heat is now almost unbearably hot without blending cool air.